Patent Publication Number: US-11646543-B2

Title: Optical phased array dynamic beam shaping with noise correction

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Application No. PCT/IL2018/051184, filed Nov. 6, 2018, claiming priority to Israel Patent Application No. 255496, entitled OPTICAL PHASED ARRAY DYNAMIC BEAM SHAPING WITH NOISE CORRECTION, filed Nov. 7, 2017; to Israel Patent Application No. 256107, entitled ‘ SEED LASER FAILURE PROTECTION SYSTEM’, filed Dec. 4, 2017; to U.S. Provisional Patent Application Ser. No. 62/594,167, entitled ‘LASER BACK-REFLECTION PROTECTION USING OPTICAL PHASED ARRAY LASER’, filed Dec. 4, 2017; to Israel Patent Application No. 258936, entitled ‘ SCALED PHASE MODIFICATION, PHASE CALIBRATION AND SEED LASER PROTECTION IN OPTICAL PHASED ARRAY’, filed Apr. 25, 2018; to U.S. Provisional Patent Application No. 62/684,341, entitled ‘MULTIPLE DETECTORS AND CORRESPONDING MULTIPLE CLOSELY SPACED OPTICAL PATHWAYS IN OPTICAL PHASED ARRAY LASER’, filed Jun. 13, 2018; and to U.S. Provisional Patent Application No. 62/702,957, entitled ‘DETECTOR MASK IN OPTICAL PHASED ARRAY LASER’, filed Jul. 25, 2018, the disclosures of all of which are hereby incorporated by reference and priorities of all of which are hereby claimed pursuant to 37 CFR 1.78(a)(4) and (5)(i). 
     Reference is also made to U.S. Pat. No. 9,893,494, the disclosure of which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to laser coherent beam combining and more particularly to optical phased arrays. 
     BACKGROUND OF THE INVENTION 
     Various types of optical phased arrays are known in the art. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to provide systems and methods relating to noise correction and phase modification in dynamically shaped beams produced by laser optical phased arrays. 
     There is thus provided in accordance with a preferred embodiment of the present invention a laser system including a seed laser, a laser beam splitting and combining subsystem receiving an output from the seed laser and providing a combined laser output having noise and a noise cancellation subsystem operative to provide a noise cancellation phase correction output based on taking into consideration the noise at intermittent times, the laser beam splitting and combining subsystem varying a phase of the combined laser output during time interstices between the intermittent times. 
     There is further provided in accordance with another preferred embodiment of the present invention a laser system including a seed laser, a laser beam splitting and combining subsystem receiving an output from the seed laser and providing a combined laser output having noise and a noise cancellation subsystem operative to provide a noise cancellation phase correction output, based on taking into consideration the noise at a noise sampling rate, the laser beam splitting and combining subsystem varying a phase of the combined laser output at a phase varying rate which exceeds the noise sampling rate. 
     Preferably, at least one of the noise sampling rate and the phase varying rate changes over time. 
     Preferably, the noise sampling rate is predetermined. 
     In accordance with a preferred embodiment of the present invention, the laser beam splitting and combining subsystem varies a phase of the combined laser output to provide spatial modulation of the combined laser output. 
     Preferably, the spatial modulation of the combined laser output is provided in combination with mechanical spatial modulation of the combined laser output, the spatial modulation in combination with the mechanical spatial modulation being faster than the mechanical spatial modulation in the absence of the spatial modulation. 
     Additionally or alternatively, the spatial modulation of the combined laser output is provided in combination with mechanical spatial modulation of the combined laser output, the spatial modulation in combination with the mechanical spatial modulation being more precise than the mechanical spatial modulation in the absence of the spatial modulation. 
     Preferably, the spatial modulation includes modulation of at least one of a shape and a diameter of the combined laser output. 
     Preferably, the laser beam splitting and combining subsystem provides laser beam amplification downstream of the splitting and upstream of the combining. 
     In accordance with a further preferred embodiment of the present invention, the noise cancellation phase correction output is calculated based on sequentially applying at least two phase changes to at least one constituent beam of the combined laser output and identifying one phase change of the at least two phase changes corresponding to a maximum output intensity of the at least one constituent beam. 
     Preferably, the system also includes at least one detector cooperatively coupled to the noise cancellation subsystem for detecting at least a portion of the combined laser output. 
     Preferably, the at least one detector performs the detecting continuously. 
     In accordance with an additionally preferred embodiment of the present invention, the noise cancellation phase correction output cancels intensity noise in the combined laser output. 
     Preferably, the system also includes at least one intensity modulator for varying an intensity of the combined laser output. 
     In accordance with a still additionally preferred embodiment of the present invention, the noise cancellation phase correction output cancels position noise in the combined laser output. 
     Preferably, the system also includes at least one position modulator for varying a position of the combined laser output. 
     Preferably, a laser cutting system includes the laser system of the present invention. 
     Additionally or alternatively, a laser additive manufacturing system includes the laser system of the present invention. 
     Still additionally or alternatively, a laser welding system includes the laser system of the present invention. 
     Further additionally or alternatively, a free-space optical communication system includes the laser system of the present invention. 
     There is also provided in accordance with a preferred embodiment of the present invention a method for performing noise correction on a phase varied laser output including receiving an output from a seed laser, splitting and combining the output to provide a combined laser output having noise, applying a noise cancellation phase correction output to the combined laser output based on taking into consideration the noise at intermittent time, and varying a phase of the combined laser output during time interstices between the intermittent times. 
     There is further provided in accordance with another preferred embodiment of the present invention a method for performing noise correction on a phase varied laser output including receiving an output from a seed laser, splitting and combining the output to provide a combined laser output having noise, applying a noise cancellation phase correction output to the combined laser output, based on taking into consideration the noise at a noise sampling rate, and varying a phase of the combined laser output at a phase varying rate which exceeds the noise sampling rate. 
     Preferably, at least one of the noise sampling rate and the phase varying rate changes over time. 
     Preferably, the noise sampling rate is predetermined. 
     In accordance with a preferred embodiment of the present invention, the varying of the phase provides spatial modulation of the combined laser output. 
     Preferably, the spatial modulation of the combined laser output is provided in combination with mechanical spatial modulation of the combined laser output, the spatial modulation in combination with the mechanical spatial modulation being faster than the mechanical spatial modulation in the absence of the spatial modulation. 
     Additionally or alternatively, the spatial modulation of the combined laser output is provided in combination with mechanical spatial modulation of the combined laser output, the spatial modulation in combination with the mechanical spatial modulation being more precise than the mechanical spatial modulation in the absence of the spatial modulation. 
     Preferably, the spatial modulation includes modulation of at least one of a shape and a diameter of the combined laser output. 
     Preferably, the method also includes amplifying the output, downstream of the splitting and upstream of the combining. 
     In accordance with another preferred embodiment of the present invention, the method also includes calculating the noise cancellation phase correction output based on sequentially applying at least two phase changes to at least one constituent beam of the combined laser output and identifying one phase change of the at least two phase changes corresponding to a maximum output intensity of the at least one constituent beam. 
     Preferably, the method also includes detecting at least a portion of the combined laser output. 
     Preferably, the detecting is performed continuously. 
     In accordance with yet another preferred embodiment of the present invention, the noise cancellation phase correction output cancels intensity noise in the combined laser output. 
     Preferably, the method also includes modulating an intensity of the output, downstream of the splitting and upstream of the combining. 
     In accordance with still another preferred embodiment of the present invention, the noise cancellation phase correction output cancels position noise in the combined laser output. 
     Preferably, the method also includes modulating a position of the output, downstream of the splitting and upstream of the combining. 
     Preferably, a method for laser cutting includes the method of the present invention. 
     Additionally or alternatively, a method for additive manufacturing includes the method of the present invention. 
     Further additionally or alternatively, a method for laser welding includes the method of the present invention. 
     Still further additionally or alternatively, a method for free space optical communication includes the method of the present invention. 
     There is also provided in accordance with another preferred embodiment of the present invention a laser system including a seed laser, a laser beam splitting and combining subsystem receiving an output from the seed laser and providing a combined laser output, the laser beam splitting and combining subsystem varying a phase of the combined laser output, a plurality of detectors detecting the combined laser output at intermittent times during the varying of the phase of the combined laser output and a plurality of optical pathways between the combined laser output and the plurality of detectors for providing therealong the combined laser output to the plurality of detectors, a spatial density of the plurality of optical pathways being greater than a spatial density of the plurality of detectors. 
     Preferably, the combined laser output has noise and the laser system also includes a noise cancellation subsystem operative to provide a noise cancellation phase correction output based on taking into consideration the noise of the combined laser output, as detected by the plurality of detectors at the intermittent times during the varying of the phase of the combined laser output. 
     Preferably, the plurality of optical pathways includes a plurality of optical fibers, ends of the optical fibers being arranged with the spatial density greater than the spatial density of the plurality of detectors. 
     Preferably, ones the plurality of optical pathways are interspaced by a distance of 20-1000 microns. 
     Preferably, ones of the plurality of detectors are interspaced by a distance of 5-50 mm. 
     There is additionally provided in accordance with another preferred embodiment of the present invention method for detecting a laser output including receiving an output from a seed laser, splitting and combining the output to provide a combined laser output, varying a phase of the combined laser output and providing the combined laser output to a plurality of detectors along a plurality of optical pathways, a spatial density of the plurality of optical pathways being greater than a spatial density of the plurality of detectors. 
     Preferably, the combined laser output has noise and the method also includes providing a noise cancellation phase correction output based on taking into consideration the noise of the combined laser output, as detected by the plurality of detectors during the varying of the phase of the combined laser output. 
     Preferably, the plurality of optical pathways includes a plurality of optical fibers, ends of the optical fibers being arranged with the spatial density greater than the spatial density of the plurality of detectors. 
     Preferably, ones the plurality of optical pathways are interspaced by a distance of 20-1000 microns. 
     Preferably, ones of the plurality of detectors are interspaced by a distance of 5-50 mm. 
     There is further provided in accordance with yet another preferred embodiment of the present invention a laser system including a seed laser, a laser beam splitting and combining subsystem receiving an output from the seed laser and providing a combined laser output, the laser beam splitting and combining subsystem varying a phase of the combined laser output, at least one detector detecting the combined laser output during the varying of the phase of the combined laser output and an optical mask including at least one of a transmissive region and a reflective region for respectively providing therethrough and therefrom the combined laser output to the at least one detector. 
     Preferably, at least one of the transmissive region and the reflective region is configured in accordance with at least one of a shape and a trajectory of the combined laser output. 
     Preferably, the system also includes a focusing subsystem interfacing the optical mask and the at least one detector for focusing the combined laser output onto the at least one detector. 
     Preferably, the focusing subsystem includes at least one focusing lens. 
     Preferably, the at least one detector includes a single detector. 
     In accordance with a preferred embodiment of the present invention, the transmissive region has non-uniform transparency. 
     Preferably, the non-uniform transparency of the transmissive region compensates for non-noise related non-uniformity in intensity of the combined laser output. 
     Preferably, the optical mask includes an electrically modulated device and the at least one of the transmissive region and the reflective region is electronically modifiable. 
     Preferably, the optical mask includes an LCD screen. 
     In accordance with another preferred embodiment of the present invention, the reflective region has non-uniform reflectivity. 
     Preferably, the non-uniform reflectivity of the reflective region compensates for non-noise related non-uniformity in intensity of the combined laser output. 
     Preferably, the reflective region includes a DMM. 
     Preferably, the combined laser output has noise and the laser system also includes a noise cancellation subsystem operative to provide a noise cancellation phase correction output based on taking into consideration the noise of the combined laser output, as detected by the at least one detector during the varying of the phase of the combined laser output. 
     There is still further provided in accordance with still a further preferred embodiment of the present invention a method for detecting a laser output including receiving an output from a seed laser, splitting and combining the output to provide a combined laser output, varying a phase of the combined laser output, providing, by an optical mask, the combined laser output to at least one detector, the optical mask including at least one of a transmissive region and a reflective region for respectively providing therethrough and therefrom the combined laser output to the at least one detector and detecting, by the at least one detector, the combined laser output during the varying of the phase. 
     Preferably, the at least one of the transmissive region and the reflective region is configured in accordance with at least one of a shape and a trajectory of the combined laser output. 
     Preferably, the method also includes focusing the combined laser output onto the at least one detector. 
     Preferably, the method also includes providing a focusing lens interfacing the optical mask and the at least one detector, for performing the focusing. 
     Preferably, the at least one detector includes a single detector. 
     In accordance with a preferred embodiment of the present invention, the transmissive region has non-uniform transparency. 
     Preferably, the non-uniform transparency of the transmissive region compensates for non-noise related non-uniformity in intensity of the combined laser output. 
     Preferably, the optical mask includes an electrically modulated device and the at least one of the transmissive region and the reflective region is electronically modifiable. 
     Preferably, the optical mask includes an LCD screen. 
     In accordance with another preferred embodiment of the present invention, the reflective region has non-uniform reflectivity. 
     Preferably, the non-uniform reflectivity of the reflective region compensates for non-noise related non-uniformity in intensity of the combined laser output. 
     Preferably, the reflective region includes a DMM. 
     Preferably, the combined laser output has noise and the method also includes providing a noise cancellation phase correction output based on taking into consideration the noise of the combined laser output, as detected by the at least one detector during the varying of the phase of the combined laser output. 
     There is also provided in accordance with yet another preferred embodiment of the present invention a laser system including a seed laser, a laser splitting and combining subsystem receiving an output from the seed laser and combining the output to provide a combined laser output, a phase modulation subsystem for varying a phase of the combined laser output and a voltage-to-phase correlation subsystem for correlating a voltage applied to the phase modulation subsystem to a phase modulating output produced by the phase modulation subsystem and for providing a voltage-to-phase correlation output useful in calibrating the phase modulation subsystem, the correlating being performed periodically during the varying of the phase. 
     Preferably, the phase modulation subsystem includes a plurality of phase modulators. 
     Preferably, the voltage is applied to the plurality of phase modulators by a phase modulation control module. 
     Preferably, the voltage includes a voltage intended to produce a phase shift of the combined laser output of 2π. 
     Preferably, the correlating includes measuring a change in intensity of a far-field intensity pattern of the combined laser output following application of the voltage and deriving a relationship between the voltage and a phase shift corresponding to the change in intensity. 
     Preferably, the voltage is sequentially applied to ones of the plurality of phase modulators. 
     Preferably, the correlating is performed at a slower rate than the varying of the phase. 
     Preferably, the varying of the phase is performed at a rate of 1 million times per second and the correlating is performed at a rate of once per second. 
     There is additionally provided in accordance with an additionally preferred embodiment of the present invention a method for performing phase calibration of a laser system including receiving an output from a seed laser, splitting and combining the output to provide a combined laser output, varying a phase of the combined laser output by a phase modulation subsystem, periodically during the varying of the phase, applying a voltage to the phase modulation subsystem and correlating the voltage to a phase modulating output produced by the phase modulation subsystem and providing a voltage-to-phase correlation output useful in calibrating the phase modulation subsystem. 
     Preferably, the phase modulation subsystem includes a plurality of phase modulators. 
     Preferably, applying the voltage is performed by a phase modulation control module. 
     Preferably, the voltage includes a voltage intended to produce a phase shift of the combined laser output of 2π. 
     Preferably, the correlating includes measuring a change in intensity of a far-field intensity pattern of the combined laser output following application of the voltage and deriving a relationship between the voltage and a phase shift corresponding to the change in intensity. 
     Preferably, the method also includes sequentially applying the voltage to ones of the plurality of phase modulators. 
     Preferably, the correlating is performed at a slower rate than the varying of the phase. 
     Preferably, the varying of the phase is performed at a rate of 1 million times per second and the correlating is performed at a rate of once per second. 
     There is also provided in accordance with another preferred embodiment of the present invention a laser system including a seed laser, a laser beam splitting and combining subsystem receiving an output from the seed laser, splitting the output into a plurality of sub-beams and providing a combined laser output including the plurality of sub-beams and a phase modulation subsystem grouping at least a portion of ones of the plurality of sub beams into a multiplicity of groups of sub-beams, the phase modulation subsystem in parallel across the multiplicity of groups of sub-beams, varying a phase of each sub-beam within each group relative to phases of other sub-beams within the group so as to vary a phase of each group, and varying the phase of each group relative to phases of other ones of the multiplicity of groups, thereby varying a phase of the combined laser output. 
     Preferably, the phase modulation subsystem includes at least one cylindrical lens for performing the grouping. 
     Alternatively, the phase modulation subsystem includes an array of mirrors and corresponding focusing lenses for performing the grouping. 
     Preferably, the phase modulation subsystem includes a plurality of phase modulators for varying the phases of the sub-beams. 
     Preferably, the phase modulation subsystem includes at least one electronic control module in operative control of the plurality of phase modulators. 
     Preferably, the phase modulation subsystem includes a multiplicity of detectors corresponding to the multiplicity of groups, for detecting a far field intensity pattern of each of the multiplicity of groups. 
     In accordance with a preferred embodiment of the present invention, the system also includes a multiplicity of optical masks masking corresponding ones of the multiplicity of detectors, each optical mask including at least one of a transmissive region and a reflective region for respectively providing therethrough and therefrom the far field intensity pattern to the corresponding detector of the multiplicity of detectors. 
     Preferably, the multiplicity of detectors performs the detecting at least partially mutually simultaneously. 
     Preferably, the phase modulation subsystem includes an additional auxiliary detector for detecting a combined far field intensity pattern of the multiplicity of groups. 
     Preferably, the phase modulation subsystem includes a multiplicity of additional phase modulators, each additional phase modulator being common to all sub-beams within each the group for varying the phase of each group relative to phases of other ones of the multiplicity of groups. 
     Preferably, the phase modulation subsystem includes an additional electronic control module in operative control of the multiplicity of additional phase modulators. 
     In accordance with another preferred embodiment of the present invention, each detector of the multiplicity of detectors includes a plurality of detectors. 
     Preferably, the system also includes a plurality of optical pathways between the far field intensity pattern of each of the multiplicity of groups and each plurality of detectors for providing the far field intensity pattern therealong to the plurality of detectors, a spatial density of the plurality of optical pathways being greater than a spatial density of the plurality of detectors. 
     Preferably, the varying of the phase of the combined laser output includes maximizing an intensity of the combined laser output. 
     Preferably, the varying of the phase of the combined laser output provides spatial modulation of the combined laser output, without involving mechanical spatial modulation of the combined laser output. 
     Preferably, the laser beam splitting and combining subsystem provides laser beam amplification downstream of the splitting and upstream of the combining. 
     There is further provided in accordance with still another preferred embodiment of the present invention a method for performing phase variation of a laser output including receiving a laser output from a seed laser, splitting the laser output into a plurality of sub-beams and combining the plurality of sub-beams to provide a combined laser output, grouping at least a portion of ones of the plurality of sub-beams into a multiplicity of groups of sub-beams, in parallel across the multiplicity of groups of sub-beams, varying a phase of each sub-beam within each group relative to phases of other sub-beams within the group so as to vary a phase of each group and varying the phase of each group relative to phases of other ones of the multiplicity of groups, thereby varying a phase of the combined laser output. 
     Preferably, the grouping is performed by at least one cylindrical lens. 
     Alternatively, the grouping is performed by an array of mirrors and corresponding focusing lenses. 
     Preferably, the varying of the phases of the sub-beams is performed by a plurality of phase modulators. 
     Preferably, the method also includes controlling the plurality of phase modulators by at least one electronic control module. 
     Preferably, the method also includes detecting a far field intensity pattern of each of the multiplicity of groups, by a corresponding multiplicity of detectors. 
     In accordance with a preferred embodiment of the present invention, the method includes providing, by a multiplicity of optical masks, the far field intensity pattern to corresponding ones of the multiplicity of detectors, each optical mask including at least one of a transmissive region and a reflective region for respectively providing therethrough and therefrom the far field intensity pattern to the corresponding detector of the multiplicity of detectors. 
     Preferably, the detecting is performed at least partially mutually simultaneously for the multiplicity of groups. 
     Preferably, the method also includes detecting a combined far field intensity pattern of the multiplicity of groups, by an auxiliary detector. 
     Preferably, the varying of the phase of each group relative to phases of other ones of the multiplicity of groups is performed by a multiplicity of additional phase modulators, each additional phase modulator being common to all sub-beams within each the group. 
     Preferably, the method also includes controlling the multiplicity of additional phase modulators by an additional electronic control module. 
     In accordance with another preferred embodiment of the present invention, each detector of the multiplicity of detectors includes a plurality of detectors. 
     Preferably, the method also includes providing the far field intensity pattern of each of the multiplicity of groups to each plurality of detectors along a plurality of optical pathways, a spatial density of the plurality of optical pathways being greater than a spatial density of the plurality of detectors. 
     Preferably, the varying of the phase of the combined laser output includes maximizing an intensity of the combined laser output. 
     Preferably, the varying of the phase of the combined laser output provides spatial modulation of the combined laser output, without involving mechanical spatial modulation of the combined laser output. 
     Preferably, the method also includes amplifying the laser output downstream of the splitting and upstream of the combining. 
     There is still further provided in accordance with another preferred embodiment of the present invention a laser system including an optical phased array laser including a seed laser and a laser beam splitting and combining subsystem receiving a laser output from the seed laser and providing a combined laser output, the laser beam splitting and combining subsystem varying a phase of the combined laser output to focus the combined laser output on a substrate, the combined laser output not being focused on the substrate in the absence of the varying of the phase. 
     Preferably, the system also includes an optical element receiving the combined laser output from the laser beam splitting and combining subsystem and focusing the combined laser output at a focal point not coincident with the substrate. 
     Preferably, laser beams back-scattered from the substrate are not focused on the optical phased array laser. 
     There is yet further provide in accordance with still another preferred embodiment of the present invention a method for focusing of laser beams in a laser system including receiving a laser output from a seed laser, splitting and combining the laser output to provide a combined laser output and varying a phase of the combined laser output to focus the combined laser output on a substrate, the combined laser output not being focused on the substrate in the absence of the varying of the phase. 
     Preferably, the method also includes focusing the combined laser output, by an optical element, at a focal point not coincident with the substrate. 
     Preferably, laser beams back-scattered from the substrate are not focused on the laser system. 
     There is additionally provided in accordance with a still additionally preferred embodiment of the present invention a laser amplifier system including a seed laser providing a laser output, an amplifying subsystem receiving the laser output from the seed laser along a first optical path and providing an amplified laser output and a detector subsystem receiving the laser output from the seed laser along a second optical path, the detector subsystem being operative to deactivate the amplifying subsystem upon detection by the detector subsystem of at least one fault in the laser output, a first time of flight of the laser output along the first optical path from the seed laser to the amplifying subsystem being greater than a combination of a second time of flight of the laser output along the second optical path from the seed laser to the detector subsystem and a time taken for the detector subsystem to deactivate the amplifying subsystem. 
     Preferably, the first optical path includes a coiled optical fiber. 
     Preferably, the at least one fault includes at least one of reduction of power of the laser output and degradation of line width of the laser output. 
     Preferably, the amplifying subsystem includes a power amplifier and the laser amplifier system includes a MOPA. 
     There is yet additionally provided in accordance with yet an additionally preferred embodiment of the present invention a method for preventing damage to an amplifying subsystem in a laser system including receiving a laser output from a seed laser along a first optical path, amplifying the laser output to provide an amplified laser output, receiving a laser output from the seed laser along a second optical path, detecting at least one fault in the laser output received along the second optical path and stopping the amplifying upon the detecting of the at least one fault in the laser output, a first time of flight of the laser output along the first optical path being greater than a combination of a second time of flight of the laser output along the second optical path and a time taken for the stopping of the amplifying to be implemented. 
     Preferably, the first optical path includes a coiled optical fiber. 
     Preferably, the at least one fault includes at least one of reduction of power of the laser output and degradation of line width of the laser output. 
     Preferably, the amplifying subsystem includes a power amplifier and the laser amplifier system includes a MOPA. 
     There is also provided in accordance with still another preferred embodiment of the present invention a laser amplifier system including a seed laser providing a laser output, a first amplifier arranged to receive the laser output from the seed laser, the first amplifier providing a first amplified laser output upon receipt of the laser output from the seed laser and providing one of amplified spontaneous emission and an additional laser output upon cessation of receipt of the laser output from the seed laser and a second amplifier receiving one of the first amplified laser output, the amplified spontaneous emission and the additional laser output from the first amplifier and providing a second amplified laser output, amplification provided by the second amplifier being greater than amplification provided by the first amplifier. 
     Preferably, the system also includes a filter structure downstream of the seed laser and upstream of the first amplifier. 
     Preferably, the filter structure includes a beam splitter splitting the laser output along a first and a second optical path, the first optical path being longer than the second optical path, a detector detecting a combined laser output from the first and second optical paths, an electronic control module coupled to the detector, for receiving an output from the detector and a phase control module located along one of the first and second optical paths, the phase control module being operated by the electronic control module to modify a phase of the laser output responsive to detection by the detector of interference in the combined laser output. 
     There is further provided in accordance with a still further preferred embodiment of the present invention a method for preventing damage to an amplifier in a laser system including receiving a laser output from a seed laser, providing, by a first amplifier, a first amplified laser output upon receipt of the laser output from the seed laser, providing, by the first amplifier, one of amplified spontaneous emission and an additional laser output upon cessation of the receipt of the laser output from the seed laser and receiving, by a second amplifier, one of the first amplified laser output, the amplified spontaneous emission and the additional laser output and providing a second amplified laser output, the second amplified laser output being greater than the first amplified laser output. 
     Preferably, the method also includes filtering the laser output downstream from the seed laser and upstream from the first amplifier. 
     Preferably, the filtering includes splitting the laser output along a first and a second optical path, the first optical path being longer than the second optical path, detecting, by a detector, a combined laser output from the first and second optical paths, receiving, by an electronic control module, an output from the detector and modifying a phase of the laser output along one of the first and second optical paths, responsive to detection by the detector of interference in the combined laser output. 
     There is still further provided in accordance with another preferred embodiment of the present invention a laser amplifier system including a seed laser providing a first laser output having a first power, an amplifying subsystem receiving the first laser output from the seed laser and providing an amplified laser output and an auxiliary laser subsystem providing a second laser output at least upon cessation of the first laser output, the second laser output having a second power lower than the first power. 
     Preferably, the auxiliary laser subsystem includes an additional seed laser providing the second laser output to the amplifying subsystem at least concurrently with the providing of the first laser output. 
     Alternatively, the amplifying subsystem includes an entry at which the first laser output is received and an exit at which the amplified laser output is provided and the laser amplifier system includes a first reflection grating positioned at the entry and a second reflection grating positioned at the exit, the first and second reflection gratings in combination with the amplifying subsystem including the auxiliary laser subsystem. 
     Preferably, the first and second reflection gratings are reflective in a wavelength range of 1090 nm-1100 nm. 
     Preferably, the second laser output is of a different wavelength than the first laser output. 
     Preferably, the system also includes a filter downstream of the seed laser and upstream of the amplifying subsystem. 
     Preferably, the filter includes a beam splitter splitting the first laser output along a first optical path and a second optical path, the first optical path being longer than the second optical path, a detector detecting a combined laser output from the first and second optical paths, an electronic control module coupled to the detector, for receiving an output from the detector and a phase control module located along one of the first and second optical paths, the phase control module being operated by the electronic control module to modify a phase of the first laser output responsive to detection by the detector of interference in the combined laser output. 
     Preferably, the system also includes a detector subsystem for detecting the first laser output from the seed laser. 
     Preferably, the detector subsystem includes a splitter splitting the first laser output into a first portion and a second portion, an additional amplifier amplifying the second portion and providing an amplified output and an optical fiber receiving the amplified output, the optical fiber being configured to exhibit non-linear effects upon a line width of the first laser output becoming unacceptably narrow. 
     Preferably, the optical fiber has a length of 25 m and a core diameter of 6 microns. 
     There is yet additionally provided in accordance with another preferred embodiment of the present invention a method for preventing damage to an amplifier in a laser system including providing a first laser output having a first power, amplifying the first laser output by an amplifier, to provide an amplified laser output and providing a second laser output at least upon cessation of the providing of the first laser output, the second laser output having a second power lower than the first power. 
     Preferably, the providing of the second laser output is performed at least concurrently with the providing of the first laser output. 
     Preferably, the amplifier includes an entry at which the first laser output is received and an exit at which the amplified laser output is provided, and also including positioning a first reflection grating at the entry and a second reflection grating at the exit, the first and second reflection gratings in combination with the amplifier providing the second laser output. 
     Preferably, the first and second reflection gratings are reflective in a wavelength range of 1090 nm-1100 nm. 
     Preferably, the second laser output is of a different wavelength than the first laser output. 
     Preferably, the method also includes filtering the first laser output upstream of the amplifying of the first laser output. 
     Preferably, the method includes splitting the first laser output along a first and a second optical path, the first optical path being longer than the second optical path, detecting by a detector a combined laser output from the first and second optical paths, receiving, by an electronic control module, an output from the detector and modifying a phase of the first laser output along one of the first and second optical paths, based on the output from the detector and responsive to detection by the detector of interference in the combined laser output. 
     Preferably, the method also includes detecting the first laser output. 
     Preferably, the detecting includes splitting the first laser output into a first portion and a second portion, amplifying the second portion and providing an amplified output and receiving the amplified output by an optical fiber, the optical fiber being configured to exhibit non-linear effects upon a line width of the first laser output becoming unacceptably narrow. 
     Preferably, the optical fiber has a length of 25 m and a core diameter of 6 microns. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be understood and appreciated more fully based on the following detailed description taken in conjunction with the drawings in which: 
         FIG.  1 A  is a simplified schematic illustration of an optical phased array laser system for noise corrected dynamic beam shaping, constructed and operative in accordance with a preferred embodiment of the present invention; 
         FIGS.  1 B and  1 C  are simplified graphical representations of phase variation and noise correction in a system of the type illustrated in  FIG.  1 A ; 
         FIG.  2 A  is a simplified schematic illustration of an optical phased array laser system for noise corrected dynamic beam shaping, constructed and operative in accordance with another preferred embodiment of the present invention; 
         FIGS.  2 B and  2 C  are simplified graphical representations of phase variation and noise correction in a system of the type illustrated in  FIG.  2 A ; 
         FIG.  3 A  is a simplified schematic illustration of an optical phased array laser system for noise corrected dynamic beam shaping, constructed and operative in accordance with a further preferred embodiment of the present invention; 
         FIGS.  3 B and  3 C  are simplified graphical representations of phase variation and noise correction in a system of the type illustrated in  FIG.  3 A ; 
         FIG.  4 A  is a simplified schematic illustration of an optical phased array laser system for noise corrected dynamic beam shaping, constructed and operative in accordance with a still further preferred embodiment of the present invention; 
         FIGS.  4 B and  4 C  are simplified graphical representations of phase variation and noise correction in a system of the type illustrated in  FIG.  4 A ; 
         FIGS.  5 A- 5 G  are simplified illustrations of possible far-field motion of an output of an optical phased array laser system of any of the types illustrated in  FIGS.  1 A- 4 C ; 
         FIG.  6    is a simplified schematic illustration of an optical phased array laser system including multiple detectors and corresponding multiple closely spaced optical pathways, constructed and operative in accordance with yet another preferred embodiment of the present invention; 
         FIG.  7    is a simplified schematic illustration of an optical phased array laser system including multiple detectors and corresponding multiple closely spaced optical pathways, constructed and operative in accordance with still another preferred embodiment of the present invention; 
         FIG.  8    is a simplified schematic illustration of an optical phased array laser system including multiple detectors and corresponding multiple closely spaced optical pathways, constructed and operative in accordance with yet a further preferred embodiment of the present invention; 
         FIG.  9    is a simplified schematic illustration of an optical phased array laser system including a detector mask configured in accordance with an exemplary laser beam trajectory, constructed and operative in accordance with a preferred embodiment of the present invention; 
         FIG.  10    is a simplified schematic illustration of a detector mask of the type illustrated in  FIG.  9    showing varying levels of transparency thereof; 
         FIG.  11    is a simplified schematic illustration of an optical phased array laser system including a detector mask configured in accordance with an exemplary laser beam shape, constructed and operative in accordance with another preferred embodiment of the present invention; 
         FIG.  12    is a simplified schematic illustration of a detector mask of the type illustrated in  FIG.  11   , showing varying levels of transparency thereof; 
         FIG.  13    is a simplified schematic illustration of an optical phased array laser system including voltage-phase correlating functionality, constructed and operative in accordance with a preferred embodiment of the present invention; 
         FIG.  14    is a simplified flow chart illustrating steps for performing voltage-phase correlation in a system of the type illustrated in  FIG.  13   ; 
         FIG.  15    is a simplified schematic plan view illustration of an optical phased array laser system including scaled phase modification of dynamic beams, constructed and operative in accordance with an additional preferred embodiment of the present invention; 
         FIG.  16    is a simplified schematic plan view illustration of an optical phased array laser system including scaled phase modification of dynamic beams, constructed and operative in accordance with yet an additional preferred embodiment of the present invention; 
         FIGS.  17 A and  17 B  are simplified top and perspective views of an optical phased array laser system including scaled phase modification of dynamic beams of a type illustrated in  FIG.  15    or  FIG.  16   ; 
         FIG.  18    is a simplified schematic plan view illustration of an optical phased array laser system including scaled phase modification of dynamic beams, constructed and operative in accordance with a further preferred embodiment of the present invention; 
         FIG.  19    is a simplified schematic plan view illustration of an optical phased array laser system including scaled phase modification of dynamic beams, constructed and operative in accordance with yet a further preferred embodiment of the present invention; 
         FIGS.  20 A and  20 B  are simplified top and perspective views of an optical phased array laser system including scaled phase modification of dynamic beams of a type illustrated in  FIG.  18    or  FIG.  19   ; 
         FIG.  21    is a simplified schematic plan view illustration of an optical phased array laser system including scaled phase modification of dynamic beams, constructed and operative in accordance with a still further preferred embodiment of the present invention; 
         FIGS.  22 A and  22 B  are simplified schematic illustrations of respective first and second focal states of an optical phased array laser system constructed and operative in accordance with a preferred embodiment of the present invention; 
         FIG.  23    is a simplified representation of back-scatter in an optical phased array laser system of the type illustrated in  FIGS.  22 A and  22 B ; 
         FIG.  24    is a simplified schematic diagram of a laser amplifying system including a seed laser failure protection system constructed and operative in accordance with a preferred embodiment of the present invention; 
         FIG.  25    is a simplified schematic diagram of a laser amplifying system including a seed laser failure protection system constructed and operative in accordance with another preferred embodiment of the present invention; 
         FIG.  26    is a simplified schematic diagram of a laser amplifying system including a seed laser failure protection system constructed and operative in accordance with a further preferred embodiment of the present invention; 
         FIG.  27    is a simplified schematic diagram of a laser amplifying system including a seed laser failure protection system constructed and operative in accordance with yet another preferred embodiment of the present invention; 
         FIG.  28    is a simplified schematic diagram of a laser amplifying system including a seed laser failure protection system constructed and operative in accordance with still another preferred embodiment of the present invention; 
         FIG.  29    is a simplified schematic illustration of a laser amplification system including a seed laser failure protection system constructed and operative in accordance with yet a further preferred embodiment of the present invention; 
         FIG.  30    is a simplified schematic illustration of a laser amplification system including a seed laser failure protection system constructed and operative in accordance with a still further preferred embodiment of the present invention; 
         FIG.  31    is a simplified schematic illustration of a laser amplification system including a seed laser failure protection system constructed and operative in accordance with yet an additional preferred embodiment of the present invention; 
         FIG.  32    is a simplified schematic illustration of a laser amplification system including a seed laser failure protection system constructed and operative in accordance with a still additional preferred embodiment of the present invention; and 
         FIG.  33    is a simplified schematic illustration of a sensor useful in a laser amplification system of any of the types illustrated in  FIGS.  24 - 32   . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference is now made to  FIG.  1 A , which is a simplified schematic illustration of an optical phased array laser system for noise corrected dynamic beam shaping, constructed and operative in accordance with a preferred embodiment of the present invention; and to  FIGS.  1 B and  1 C , which are simplified graphical representations of phase variation and noise correction in a system of the type illustrated in  FIG.  1 A . 
     As seen in  FIG.  1 A , there is provided an optical phased array (OPA) laser system  100 , here shown to be employed, by way of example, within a laser cutting system  102 . Laser cutting system  102  may include OPA laser system  100  mounted in spaced relation to a multi-axis positioning table  104 , upon which table  104  an item, such as an item  106 , may be cut using laser system  100 , as is detailed henceforth. It is understood that although laser cutting system  102  is illustrated herein in the context of table  104 , system  102  may be embodied as any type of laser cutting system, as will be appreciated by one skilled in the art 
     As best seen at an enlargement  110 , OPA laser  100  preferably comprises a seed laser  112  and a laser beam splitting and combining subsystem  114 . Splitting and combining subsystem  114  preferably receives an output laser beam from seed laser  112  and splits the output laser beam into a plurality of sub-beams along a corresponding plurality of channels  116 . Here, by way of example only, an output from seed laser  112  is shown to be split into ten sub-beams along ten channels  116  although it is appreciated that splitting and combining subsystem  114  may include a fewer or greater number of channels along which the output of seed laser  112  is split, and typically may include a far greater number of channels such as 32 or more channels. 
     The relative phase of each sub-beam may be individually modulated by a phase modulator  118 , preferably located along each of channels  116 . Each phase modulated sub-beam produced by the splitting and subsequent phase modulation of the output of seed laser  112  preferably propagates towards a collimating lens  119 . The individually collimated, phase modulated sub-beams are subsequently combined, for example at a focal lens  120 , to form an output beam  122 . 
     Splitting and combining subsystem  114  may also provide laser amplification of the sub-beams, preferably following the splitting of the output beam of seed laser  112  into sub-beams and prior to the combining of the sub-beams to form output beam  122 . Here, by way of example, splitting and combining subsystem  114  is shown to include a plurality of optical amplifiers  124  located along corresponding ones of channels  116  for amplifying each sub-beam. It is appreciated, however, that such amplification is optional and may be omitted, depending on the power output requirements of OPA laser  100 . 
     The phase of output beam  122 , and hence the position and shape of the far-field intensity pattern thereof, is controlled, at least in part, by the relative phases of the constituent sub-beams combined to form output beam  122 . In many applications, such as laser cutting as illustrated in  FIG.  1 A , it is desirable to dynamically move and shape the far-field intensity pattern of the output beam. This may be achieved in laser system  100  by laser splitting and combining subsystem  114  dynamically varying the relative phases of the individual sub-beams and thereby varying the phase of the combined laser output  122  so as dynamically to control the position and shape of the far-field intensity pattern thereof. 
     The relative phases of the sub-beams are preferably predetermined in accordance with the desired laser output pattern for the cutting of item  106 . Particularly preferably, the varying relative phases are applied by a phase control subsystem  130 . Phase control subsystem  130  preferably forms a part of a control electronics module  132  in OPA laser  100  and preferably controls each phase modulator  118  so as to dynamically modulate the relative phases of the sub-beams along channels  116 . 
     Due to noise inherent in OPA system  100 , output beam  122  has noise. Noise in output beam  122  is typically phase noise created by thermal or mechanical effects and/or by the amplification process in the case that optical amplifiers  124  are present in OPA system  100 . It is a particular feature of a preferred embodiment of the present invention that laser system  100  includes a noise cancellation subsystem  140  operative to provide a noise cancellation phase correction output in order to cancel out the noise in output beam  122  in a manner detailed henceforth. 
     Particularly preferably, noise cancellation subsystem  140  employs an algorithm to sense and correct phase noise in the combined laser output. The noise cancellation phase correction output is preferably provided by noise cancellation subsystem  140  to phase modulator  118  so as to correct phase noise in output beam  122  and thus avoid distortion of the shape and position of the far field intensity pattern of output beam  122  that would otherwise be caused by the noise. Noise cancellation subsystem  140  may be included in control electronics module  132 . 
     It is understood that output beam  122  may be additionally or alternatively affected by types of noise other than phase noise, including intensity noise. In the case of output beam  122  having intensity noise, noise cancellation subsystem  140  may be operative to provide a noise cancellation phase correction output in order to cancel out the intensity noise in output beam  122 . In such a case, OPA laser system  100  may optionally additionally include intensity modulators  142  along channels  116  for modulating the intensity of each of the sub-beams along channels  116 . 
     It is understood that output beam  122  may be additionally or alternatively affected by mechanical noise which may affect the relative position of the sub-beams. In the case of output beam  122  having position noise, noise cancellation subsystem  140  may be operative to provide a noise cancellation phase correction output in order to cancel out the position noise in output beam  122 . In such a case, OPA laser system  100  may optionally additionally include position modulators  144  along channels  116  for modulating the position of each of the sub-beams along channels  116 . 
     In order to facilitate application of phase variation and noise correction to output beam  122 , a portion of the output of OPA laser  100  is preferably extracted and directed towards at least one detector, here illustrated as a single detector  150 . Detector  150  may alternatively be embodied as multiple detectors, as detailed henceforth with reference to  FIGS.  6 - 8  and  15 - 21   . The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required noise correction and/or phase variation may be calculated. In the embodiment shown in  FIG.  1 A , plurality of sub-beams along channels  116  are directed towards a beam splitter  160 . Beam splitter  160  preferably splits each sub-beam into a transmitted portion  162  and a reflected portion  164  in accordance with a predetermined ratio. For example, beam splitter  160  may split each sub-beam with a 99.9% transmitted: 0.01% reflected ratio. 
     The transmitted portion  162  of the sub-beams preferably propagates towards focal lens  120 , at which focal lens  120  the sub-beams are combined to form output beam  122  having a far-field intensity pattern  166  incident on a surface of item  106 . The reflected portion  164  of the sub-beams is preferably reflected towards an additional focal lens  168 , at which additional focal lens  168  the sub-beams are combined to form an output reference beam  170  having a far-field intensity pattern  172  incident on a surface of detector  150 . 
     It is understood that the particular structure and configuration of beam splitting and recombining elements shown herein, including beam splitter  160  and focal lenses  120  and  168 , is exemplary only and depicted in a highly simplified form. It is appreciated that OPA laser system  100  may include a variety of such elements, as well as additional optical elements, including, by way of example only, additional or alternative lenses, optical fibers and coherent free-space far-field combiners. 
     As described hereinabove, the shape and position of far-field intensity pattern  166  of the output beam  122  and correspondingly of far-field intensity pattern  172  of the reference beam  170  are constantly changing, due to the ongoing variation of the relative phases of the sub-beams. As a result, far-field intensity pattern  172  is not fixed upon detector  150  but rather is constantly being moved around with respect to detector  150  depending on the combined relative phases of the constituent sub-beams. However, in order for detector  150  to provide the required noise cancellation phase correction output, far-field intensity pattern  172  must be incident upon detector  150  in order for detector to measure the intensity of far-field intensity pattern  172  and hence apply a noise correction accordingly, resulting in a fixed output beam. 
     The conflict between the dynamic nature of far-field intensity pattern  172  due to the phase-variation thereof and the fixed nature required of far-field intensity pattern  172  in order to derive and apply noise correction thereto, is advantageously resolved in the present invention by providing the noise cancellation and phase variation at mutually different times and rates. 
     The noise cancellation phase correction output is provided based on taking into consideration noise measured at detector  150  at a noise sampling rate. The output beam  122  is controlled in such a way that the far-field intensity pattern  172  is incident upon detector  150  during the course of the dynamic changes to the shape and position of output and reference far-field intensity patterns  166 ,  172  at a rate that is equal to or higher than the required noise sampling rate. The noise in reference beam  170  is taken into consideration during those intermittent times at which the far-field intensity pattern  172  is returned to detector  150 . 
     At time interstices between the intermittent times at which far-field intensity pattern  172  is incident upon detector  150 , the phase of the combined output beams  122  and  170  is varied in order to dynamically change the shape and position of the far-field intensity pattern thereof as required to perform laser cutting of item  106 . The combined laser output is varied at a phase varying rate which exceeds the noise sampling rate, in order to rapidly change the phase and hence shape and position of the far-field intensity pattern. By way of example, the noise sampling rate may be of the order of 10-1000 Hz whereas the phase varying rate may be greater than 10,000 Hz. 
     The different rates and time scales over which the noise cancellation and phase variation are preferably performed in embodiments of the present invention may be best understood with reference to a graph  180  seen in  FIG.  1 A  and an enlarged version thereof shown in  FIG.  1 B . 
     As seen most clearly in  FIG.  1 B , graph  180  includes an upper portion  182  displaying variation in intensity over time of far-field intensity pattern  172  as measured at detector  150  and a lower portion  184 , displaying variation over the same time period of the relative phases of a number of sub-beams contributing to output beam  122  and reference beam  170 . For the sake of simplicity, the relative phases of ten sub-beams are displayed in graph  180 , although it is appreciated that OPA system  100  and hence the explanation provided herein is applicable to a fewer or, more typically, a far greater number of sub-beams. 
     As seen in upper portion  182 , intensity peaks  186  represent measured intensity of the reference beam  170  when the far field intensity pattern  172  passes over detector  150 . As seen in lower portion  184 , intensity peaks  186  occur at intermittent times T i  at which the relative phase of each sub-beam is zero, meaning that there is no shift in phase between the sub-beams, the position of the combined output beam is therefore not being changed and the far field intensity pattern  172  is hence directly incident on the detector  150 . It is understood that detector  150  may alternatively be positioned such that the relative phase of the sub-beams thereat is non-zero. Furthermore, more than a single detector may be employed so as to allow measurement of the far field intensity pattern  172  at more than one location therealong, as detailed henceforth with reference to  FIGS.  6 - 8  and  15 - 21   . 
     Between intensity peaks  186  the measured intensity is close to zero, as the far-field intensity pattern  172  is moved to the either side of detector  150  and thus is not directly incident on the detector  150 . As appreciated from consideration of upper portion  182 , the magnitude of intensity peaks  186  is not constant due to the presence of noise in the laser output beam, which noise degrades the far field intensity pattern  172 . 
     As seen in lower portion  184 , the relative phases of the sub-beams are varied at time interstices T between  between intermittent times T i . In the phase variation function illustrated herein, the relative phases of the sub-beams are shown to be varied in a periodic, regularly repeating pattern, with equal phase shifts being applied in the positive and negative directions. It is appreciated that such a simplistic pattern is illustrative only and that the phase variation is not necessarily regularly repeating, nor necessarily symmetrical in positive and negative directions. Furthermore, it is understood that time interstices T between  preferably but not necessarily do not overlap with intermittent times T i . Additionally, it is appreciated that at least one of the phase varying rate and the noise sampling rate may be constant or may change over time. 
     Noise cancellation subsystem  140  preferably operates by taking into consideration the noise at intermittent times T i  and providing a noise cancellation phase correction output based on the noise sensed at intermittent times T i . Noise cancellation subsystem  140  preferably employs an algorithm in order to sense noise and correct for the sensed noise accordingly. 
     According to one exemplary embodiment of the present invention, noise cancellation subsystem  140  employs an algorithm in which the relative phase of one channel is changed in such a way that the relative phase is modified by a given phase change Δφ during each cycle of travel of the far-field intensity pattern  172  with respect to detector  150 . Following a number of such cycles, in which a different phase change Δφ is applied to the selected sub-beam over each cycle, the algorithm ascertains the maximum output intensity over all of the cycles and finds the optimum phase change Δφ that produced this maximum intensity. The phase change of the selected sub-beam is then fixed at the optimum phase change Δφ for subsequent cycles and the algorithm proceeds to optimize another sub-beam. 
     Graph  180  illustrates noise cancellation according to this exemplary algorithm in three sub-beams or channels A, B and C of the total of 10 sub-beams. Sub-beams A, B and C are displayed alone in  FIG.  1 C  for the sake of clarity. It is appreciated that the line style of the traces representing phase variation and noise correction of sub-beams A, B and C respectively is modified in  FIG.  1 C  in comparison to  FIGS.  1 A and  1 B , in order to aid differentiation between the various sub-beams for the purposes of the explanation hereinbelow. 
     As seen initially in the case of channel A, and appreciated most clearly from consideration of an enlargement  190 , the dashed trace represents the pattern of variation in relative phase of sub-beam A, as would be applied by phase control sub-system  130  in the absence of any noise correction. This trace may be termed A uncorrected . The dotted- and dashed trace represents the actual relative phase of sub-beam A as modified by the noise correction algorithm in order to find the optimum phase noise correction. This trace may be termed A corrected . The modified relative phase of A corrected  is shifted with respect to the non-modified relative phase of A uncorrected  by a different Δφ A  over the first five cycles of sub-beam A. The intensity  186  measured at detector  150  varies over the first five cycles of optimization of sub-beam A due to the deliberate change in relative phase shift. 
     Following the first five cycles of sub-beam A, the algorithm ascertains the maximum intensity and finds the phase change Δφ A  that produces the maximum intensity. In this case, the maximum intensity is seen to be IA max  produced by the second phase shift Δφ A . The phase change applied to relative phase variation of sub-beam A is thus fixed at the second phase shift Δφ A  for subsequent cycles and the algorithm proceeds to optimize sub-beam B. 
     It is appreciated that during the sequential cycles of optimization of sub-beam A, the relative phases of the remainder of the sub-beams are varied as usual, each at a phase varying rate that far exceeds the noise sampling rate at which the noise in sub-beam A is taken into consideration. 
     As seen further in the case of sub-beam B, and appreciated most clearly from consideration of an enlargement  192 , the thicker trace during optimization of channel B represents the pattern of variation in relative phase of sub-beam B, as would be applied by phase control sub-system  130  in the absence of any noise correction. This trace may be termed B uncorrected . The thinner trace during optimization of channel B represents the actual relative phase of sub-beam B as modified by the noise correction algorithm in order to find the optimum phase noise correction. This trace may be termed B corrected . The modified relative phase of B corrected  is shifted with respect to the non-modified relative phase of B uncorrected  by a different Δφ B  over five cycles of optimization sub-beam B. The intensity  186  measured at detector  150  varies over these five cycles of optimization sub-beam B due to the deliberate change in relative phase shift. 
     Following these five cycles of sub-beam B, the algorithm ascertains the maximum intensity and finds the phase change Δφ B  that produces the maximum intensity. In this case, the maximum intensity is seen to be IAB max  produced by the fourth phase shift Δφ B . The phase change applied to relative phase variation of sub-beam B is then fixed at the fourth phase shift Δφ B  for subsequent cycles and the algorithm proceeds to optimize sub-beam C. 
     It is appreciated that during the five cycles of optimization of sub-beam B, the relative phases of the remainder of the sub-beams are varied as usual, each at a phase varying rate that far exceeds the noise sampling rate at which the noise in sub-beam B is taken into consideration. 
     A similar optimization process is preferably implemented for sub-beam C, in which a phase change Δφ C  is applied over several cycles in order to optimize the output beam intensity and correct for intensity degradation thereof due to phase noise in sub-beam C. 
     At least one detector  150  may operate continuously in order to continuously optimize the relative phases of the sub-beams and correct for phase noise therein. However, due to a finite response time of detector  150 , detector  150  only takes into consideration the noise in reference beam  170  at intermittent times, at a relatively slow noise sampling rate. The noise sampling rate is preferably but not necessarily predetermined. The noise sampling rate may alternatively be random. 
     It is appreciated that the particular parameters of the noise correction algorithm depicted in graph  180  are exemplary only and may be readily modified, as will be understood by one skilled in the art. For example, the phase shift Δφ may be optimized over a greater or fewer number of cycles than illustrated herein, each sub-beam may be fully optimized each time the sub-beam passes over detector  150  or several sub-beams or all of the sub-beams may be optimized during each cycle in which the far-field intensity pattern passes over detector  150 . Furthermore, non-sequential noise correction optimization algorithms may alternatively be implemented, including, but not limited to, Stochastic parallel gradient descent optimization algorithms. 
     The use of dynamically shaped, noise corrected optical phased array output beams for laser cutting is highly advantageous and enables rapid beam steering, fast power modulation, fast beam focusing and beam shape tailoring. Both the speed and quality with which a material may be cut are improved using dynamically shaped, noise corrected optical phase array output in comparison to conventional laser cutting methods. It is appreciated that but for the provision of noise correction, in accordance with preferred embodiments of the present invention, the shape and position of the optical phased array output beam would be degraded, thereby degrading the quality, speed and precision of the laser cutting process. 
     In order to maintain output beam intensity as the far-field intensity pattern of the beam moves, as is advantageous in certain laser cutting applications, movement of the output beam may be controlled such that the beam spends more time at lower-intensity positions so as to compensate for reduced power delivery thereat. Additionally or alternatively, an intensity profile mask such as a neutral density (ND) filter may be applied to the output beam in order to modify the intensity thereof. 
     Reference is now made to  FIG.  2 A , which is a simplified schematic illustration of an optical phased array laser system for noise corrected dynamic beam shaping, constructed and operative in accordance with another preferred embodiment of the present invention; and to  FIGS.  2 B and  2 C , which are simplified graphical representations of phase variation and noise correction in a system of the type illustrated in  FIG.  2 A . 
     As seen in  FIG.  2 A , there is provided an optical phased array (OPA) laser system  200 , here shown to be employed, by way of example, within an additive manufacturing system  202 . Additive manufacturing system  202  may include OPA laser system  200  mounted in spaced relation to a scanning mirror  203  and multi-axis positioning table  204 , upon which table  204  an item, such as an item  206 , may be additively manufactured using laser system  200 . It is understood that although additive manufacturing system  202  is illustrated herein in the context of scanning mirror  203 , system  202  may be embodied as any type of additive manufacturing system, as will be appreciated by one skilled in the art. 
     As best seen at an enlargement  210 , OPA laser  200  preferably comprises a seed laser  212  and a laser beam splitting and combining subsystem  214 . Splitting and combining subsystem  214  preferably receives an output laser beam from seed laser  212  and splits the output laser beam into a plurality of sub-beams along a corresponding plurality of channels  216 . Here, by way of example only, an output from seed laser  212  is shown to be split into ten sub-beams along ten channels  216  although it is appreciated that splitting and combining subsystem  214  may include a fewer or greater number of channels along which the output of seed laser  212  is split, and typically may include a far greater number of channels such as 32 or more channels. 
     The relative phase of each sub-beam may be individually modulated by a phase modulator  218 , preferably located along each of channels  216 . Each phase modulated sub-beam produced by the splitting and subsequent phase modulation of the output of seed laser  212  preferably propagates towards a collimating lens  219 . The individually collimated, phase modulated sub-beams are subsequently combined, for example at a focal lens  220 , to form an output beam  222 . 
     Splitting and combining subsystem  214  may also provide laser amplification of the sub-beams, preferably following the splitting of the output beam of seed laser  212  into sub-beams and prior to the combining of the sub-beams to form output beam  222 . Here, by way of example, splitting and combining subsystem  214  is shown to include a plurality of optical amplifiers  224  located along corresponding ones of channels  216  for amplifying each sub-beam. It is appreciated, however, that such amplification is optional and may be omitted, depending on the power output requirements of OPA laser  200 . 
     The phase of output beam  222 , and hence the position and shape of the far-field intensity pattern thereof, is controlled, at least in part, by the relative phases of the constituent sub-beams combined to form output beam  222 . In many applications, such as laser additive manufacturing as illustrated in  FIG.  2 A , it is desirable to dynamically move and shape the far-field intensity pattern of the output beam. This may be achieved in laser system  200  by laser splitting and combining subsystem  214  dynamically varying the relative phases of the individual sub-beams and thereby varying the phase of the combined laser output  222  so as dynamically to control the position and shape of the far-field intensity pattern thereof. 
     The relative phases of the sub-beams are preferably predetermined in accordance with the desired laser output pattern for the 3D printing of item  206 . Particularly preferably, the varying relative phases are applied by a phase control subsystem  230 . Phase control subsystem  230  preferably forms a part of a control electronics module  232  in OPA laser  200  and preferably controls each phase modulator  218  so as to dynamically modulate the relative phases of the sub-beams along channels  216 . 
     Due to noise inherent in OPA system  200 , output beam  222  has noise. Noise in output beam  222  is typically phase noise created by thermal or mechanical effects and/or by the amplification process in the case that optical amplifiers  224  are present in OPA system  200 . It is a particular feature of a preferred embodiment of the present invention that laser system  200  includes a noise cancellation subsystem  240  operative to provide a noise cancellation phase correction output in order to cancel out the noise in output beam  222  in a manner detailed henceforth. 
     Particularly preferably, noise cancellation subsystem  240  employs an algorithm to sense and correct phase noise in the combined laser output. The noise cancellation phase correction output is preferably provided by noise cancellation subsystem  240  to phase modulator  218  so as to correct phase noise in output beam  222  and thus avoid distortion of the shape and position of the far field intensity pattern of output beam  222  that would otherwise be caused by the noise. Noise cancellation subsystem  240  may be included in control electronics module  232 . 
     It is understood that output beam  222  may be additionally or alternatively affected by types of noise other than phase noise, including intensity noise. In the case of output beam  222  having intensity noise, noise cancellation subsystem  240  may be operative to provide a noise cancellation phase correction output in order to cancel out the intensity noise in output beam  222 . In such a case, OPA laser system  200  may optionally additionally include intensity modulators  242  along channels  216  for modulating the intensity of each of the sub-beams along channels  216 . 
     It is understood that output beam  222  may be additionally or alternatively affected by mechanical noise which may affect the relative position of the sub-beams. In the case of output beam  222  having position noise, noise cancellation subsystem  240  may be operative to provide a noise cancellation phase correction output in order to cancel out the position noise in output beam  222 . In such a case, OPA laser system  200  may optionally additionally include position modulators  244  along channels  216  for modulating the position of each of the sub-beams along channels  216 . 
     In order to facilitate application of phase variation and noise correction to output beam  222 , a portion of the output of OPA laser  200  is preferably extracted and directed towards at least one detector, here illustrated as a single detector  250 . Detector  250  may alternatively be embodied as multiple detectors, as detailed henceforth with reference to  FIGS.  6 - 8  and  15 - 21   . The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required noise correction and/or phase variation may be calculated. In the embodiment shown in  FIG.  2 A , plurality of sub-beams along channels  216  are directed towards a beam splitter  260 . Beam splitter  260  preferably splits each sub-beam into a transmitted portion  262  and a reflected portion  264  in accordance with a predetermined ratio. For example, beam splitter  260  may split each sub-beam with a 99.9% transmitted: 0.01% reflected ratio. 
     The transmitted portion  262  of the sub-beams preferably propagates towards focal lens  220 , at which focal lens  220  the sub-beams are combined to form output beam  222  having a far-field intensity pattern  266  incident on scanning mirror  203 . The reflected portion  264  of the sub-beams is preferably reflected towards an additional focal lens  268 , at which additional focal lens  268  the sub-beams are combined to form an output reference beam  270  having a far-field intensity pattern  272  incident on a surface of detector  250 . 
     It is understood that the particular structure and configuration of beam splitting and recombining elements shown herein, including beam splitter  260  and focal lenses  220  and  268 , is exemplary only and depicted in a highly simplified form. It is appreciated that OPA laser system  200  may include a variety of such elements, as well as additional optical elements, including, by way of example only, additional or alternative lenses, optical fibers and coherent free-space far-field combiners. 
     As described hereinabove, the shape and position of far-field intensity pattern  266  of the output beam  222  and correspondingly of far-field intensity pattern  272  of the reference beam  270  are constantly changing, due to the ongoing variation of the relative phases of the sub-beams. As a result, far-field intensity pattern  272  is not fixed upon detector  250  but rather is constantly being moved around with respect to detector  250  depending on the combined relative phases of the constituent sub-beams. However, in order for detector  250  to provide the required noise cancellation phase correction output, far-field intensity pattern  272  must be incident upon detector  250  in order for detector to measure the intensity of far-field intensity pattern  272  and hence apply a noise correction accordingly, resulting in a fixed output beam. 
     The conflict between the dynamic nature of far-field intensity pattern  272  due to the phase-variation thereof and the fixed nature required of far-field intensity pattern  272  in order to derive and apply noise correction thereto, is advantageously resolved in the present invention by providing the noise cancellation and phase variation at mutually different times and rates. 
     The noise cancellation phase correction output is provided based on taking into consideration noise measured at detector  250  at a noise sampling rate. The output beam  222  is controlled in such a way that the far-field intensity pattern  272  is incident upon detector  250  during the course of the dynamic changes to the shape and position of output and reference far-field intensity patterns  266  and  272  at a rate that is equal to or higher than the required noise sampling rate. The noise in reference beam  270  is taken into consideration during those intermittent times at which the far-field intensity pattern  272  is returned to detector  250 . 
     At time interstices between the intermittent times at which far-field intensity pattern  272  is incident upon detector  250 , the phase of the combined output beams  222 ,  270  is varied in order to dynamically change the shape and position of the far-field intensity pattern thereof as required to perform additive manufacturing of item  206 . The combined laser output is varied at a phase varying rate which exceeds the noise sampling rate, in order to rapidly change the phase and hence shape and position of the far-field intensity pattern. By way of example, the noise sampling rate may be of the order of 10-1000 Hz whereas the phase varying rate may be greater than 10,000 Hz. 
     The different rates and time scales over which the noise cancellation and phase variation are preferably performed in embodiments of the present invention may be best understood with reference to a graph  280  seen in  FIG.  2 A  and an enlarged version thereof shown in  FIG.  2 B . 
     As seen most clearly in  FIG.  2 B , graph  280  includes an upper portion  282  displaying variation in intensity over time of far-field intensity pattern  272  as measured at detector  250  and a lower portion  284 , displaying variation over the same time period of the relative phases of a number of sub-beams contributing to output beam  222  and reference beam  270 . For the sake of simplicity, the relative phases of ten sub-beams are displayed in graph  280 , although it is appreciated that OPA system  200  and hence the explanation provided herein is applicable to a fewer or, more typically, a far greater number of sub-beams. 
     As seen in upper portion  282 , intensity peaks  286  represent measured intensity of the reference beam  270  when the far field intensity pattern  272  passes over detector  250 . As seen in lower portion  284 , intensity peaks  286  occur at intermittent times T i  at which the relative phase of each sub-beam is zero, meaning that there is no shift in phase between the sub-beams, the position of the combined output beam is therefore not being changed and the far field intensity pattern  272  is hence directly incident on the detector  250 . It is understood that detector  250  may alternatively be positioned such that the relative phase of the sub-beams thereat is non-zero. Furthermore, more than a single detector may be employed so as to allow measurement of the far field intensity pattern  272  at more than one location therealong, as detailed henceforth with reference to  FIGS.  6 - 8  and  15 - 21   . 
     Between intensity peaks  286  the measured intensity is close to zero, as the far-field intensity pattern  272  is moved to the either side of detector  250  and thus is not directly incident on the detector  250 . As appreciated from consideration of upper portion  282 , the magnitude of intensity peaks  286  is not constant due to the presence of noise in the laser output beam, which noise degrades the far field intensity pattern  272 . 
     As seen in lower portion  284 , the relative phases of the sub-beams are varied at time interstices T between  between intermittent times T i . In the phase variation function illustrated herein, the relative phases of the sub-beams are shown to be varied in a periodic, regularly repeating pattern, with equal phase shifts being applied in the positive and negative directions. It is appreciated that such a simplistic pattern is illustrative only and that the phase variation is not necessarily regularly repeating, nor necessarily symmetrical in positive and negative directions. Furthermore, it is understood that time interstices T between  preferably but not necessarily do not overlap with intermittent times T i . Additionally, it is appreciated that at least one of the phase varying rate and the noise sampling rate may be constant or may change over time. 
     Noise cancellation subsystem  240  preferably operates by taking into consideration the noise at intermittent times T i  and providing a noise cancellation phase correction output based on the noise sensed at intermittent times T i . Noise cancellation subsystem  240  preferably employs an algorithm in order to sense noise and correct for the sensed noise accordingly. 
     According to one exemplary embodiment of the present invention, noise cancellation subsystem  240  employs an algorithm in which the relative phase of one channel is changed in such a way that the relative phase is modified by a given phase change Δφ during each cycle of travel of the far-field intensity pattern  272  with respect to detector  250 . Following a number of such cycles, in which a different phase change Δφ is applied to the selected sub-beam over each cycle, the algorithm ascertains the maximum output intensity over all of the cycles and finds the optimum phase change Δφ that produced this maximum intensity. The phase change of the selected sub-beam is then fixed at the optimum phase change Δφ for subsequent cycles and the algorithm proceeds to optimize another sub-beam. 
     Graph  280  illustrates noise cancellation according to this exemplary algorithm in three sub-beams or channels A, B and C of the total of 10 sub-beams. Sub-beams A, B and C are displayed alone in  FIG.  2 C  for the sake of clarity. It is appreciated that the line style of the traces representing phase variation and noise correction of sub-beams A, B and C respectively is modified in  FIG.  2 C  in comparison to  FIGS.  2 A and  2 B , in order to aid differentiation between the various sub-beams for the purposes of the explanation hereinbelow. 
     As seen initially in the case of channel A, and appreciated most clearly from consideration of an enlargement  290 , the dashed trace represents the pattern of variation in relative phase of sub-beam A, as would be applied by phase control sub-system  230  in the absence of any noise correction. This trace may be termed A uncorrected . The dotted- and dashed trace represents the actual relative phase of sub-beam A as modified by the noise correction algorithm in order to find the optimum phase noise correction. This trace may be termed A corrected . The modified relative phase of A corrected  is shifted with respect to the non-modified relative phase of A uncorrected  by a different Δφ A  over the first five cycles of sub-beam A. The intensity  286  measured at detector  250  varies over the first five cycles of optimization of sub-beam A due to the deliberate change in relative phase shift. 
     Following the first five cycles of sub-beam A, the algorithm ascertains the maximum intensity and finds the phase change Δφ A  that produces the maximum intensity. In this case, the maximum intensity is seen to be IA max  produced by the second phase shift Δφ A . The phase change applied to relative phase variation of sub-beam A is thus fixed at the second phase shift Δφ A  for subsequent cycles and the algorithm proceeds to optimize sub-beam B. 
     It is appreciated that during the sequential cycles of optimization of sub-beam A, the relative phases of the remainder of the sub-beams are varied as usual, each at a phase varying rate that far exceeds the noise sampling rate at which the noise in sub-beam A is taken into consideration. 
     As seen further in the case of sub-beam B, and appreciated most clearly from consideration of an enlargement  292 , the thicker trace during optimization of channel B represents the pattern of variation in relative phase of sub-beam B, as would be applied by phase control sub-system  230  in the absence of any noise correction. This trace may be termed B uncorrected . The thinner trace during optimization of channel B represents the actual relative phase of sub-beam B as modified by the noise correction algorithm in order to find the optimum phase noise correction. This trace may be termed B corrected . The modified relative phase of B corrected  is shifted with respect to the non-modified relative phase of B uncorrected  by a different Δφ B  over five cycles of optimization sub-beam B. The intensity  286  measured at detector  250  varies over these five cycles of optimization sub-beam B due to the deliberate change in relative phase shift. 
     Following these five cycles of sub-beam B, the algorithm ascertains the maximum intensity and finds the phase change Δφ B  that produces the maximum intensity. In this case, the maximum intensity is seen to be IAB max  produced by the fourth phase shift Δφ B . The phase change applied to relative phase variation of sub-beam B is then fixed at the fourth phase shift Δφ B  for subsequent cycles and the algorithm proceeds to optimize sub-beam C. 
     It is appreciated that during the five cycles of optimization of sub-beam B, the relative phases of the remainder of the sub-beams are varied as usual, each at a phase varying rate that far exceeds the noise sampling rate at which the noise in sub-beam B is taken into consideration. 
     A similar optimization process is preferably implemented for sub-beam C, in which a phase change Δφ C  is applied over several cycles in order to optimize the output beam intensity and correct for intensity degradation thereof due to phase noise in sub-beam C. 
     Detector  250  may operate continuously in order to continuously optimize the relative phases of the sub-beams and correct for phase noise therein. However, due to a finite response time of detector  250 , detector  250  only takes into consideration the noise in reference beam  270  at intermittent times, at a relatively slow noise sampling rate. The noise sampling rate is preferably but not necessarily predetermined. The noise sampling rate may alternatively be random. 
     It is appreciated that the particular parameters of the noise correction algorithm depicted in graph  280  are exemplary only and may be readily modified, as will be understood by one skilled in the art. For example, the phase shift Δφ may be optimized over a greater or fewer number of cycles than illustrated herein, each sub-beam may be fully optimized each time the sub-beam passes over detector  250  or several sub-beams or all of the sub-beams may be optimized during each cycle in which the far-field intensity pattern passes over detector  250 . Furthermore, non-sequential noise correction optimization algorithms may alternatively be implemented, including, but not limited to, Stochastic parallel gradient descent optimization algorithms. 
     The use of dynamically shaped, noise corrected optical phased array output beams for laser additive manufacturing is highly advantageous and enables rapid beam steering, fast power modulation, fast beam focusing and beam shape tailoring. Both the speed and quality with which an item may be manufactured are improved using dynamically shaped, noise corrected optical phase array output in comparison to conventional laser 3D printing methods. It is appreciated that but for the provision of noise correction, in accordance with preferred embodiments of the present invention, the shape and position of the optical phased array output beam would be degraded, thereby degrading the quality, speed and precision of the laser additive manufacturing process. 
     In order to maintain output beam intensity as the far-field intensity pattern of the beam moves, as is advantageous in certain additive manufacturing applications, movement of the output beam may be controlled such that the beam spends more time at lower-intensity positions so as to compensate for reduced power delivery thereat. Additionally or alternatively, an intensity profile mask such as an ND filter may be applied to the output beam in order to modify the intensity thereof. 
     Reference is now made to  FIG.  3 A , which is a simplified schematic illustration of an optical phased array laser system for noise corrected dynamic beam shaping, constructed and operative in accordance with a further preferred embodiment of the present invention; and to  FIGS.  3 B and  3 C , which are simplified graphical representations of phase variation and noise correction in a system of the type illustrated in  FIG.  3 A . 
     As seen in  FIG.  3 A , there is provided an optical phased array (OPA) laser system  300 , here shown to be employed, by way of example, within a free space optical communication system  302 . Free space optical communication system  302  may include OPA laser system  300  mounted at an outdoor location, such as on a building, in spaced relation to a receiver  303  for receiving optical signals emanating from OPA laser  300 . It is understood that although free space optical communication system  302  is illustrated herein in the context of communication between two fixed points, free-space optical communication system  302  may be adapted for use in communications between two locations that are moving relative to one another, as will be appreciated by one skilled in the art. It is further understood that although free space optical communication system  302  is illustrated herein in the context of terrestrial communications, free-space optical communication system  302  may be adapted for use in extraterrestrial communications, as will be appreciated by one skilled in the art. 
     It is appreciated that free space optical communication system  302  is illustrated in  FIG.  3 A  as including only a single OPA laser  300  and receiver  303  for the sake of simplicity only, and may include a greater number of each, depending on the communication requirements of system  302 . It is further appreciated that receiver  303  may also be an OPA laser of a type resembling OPA laser  300  and having receiving functionality. Furthermore, OPA laser  300  may include receiving functionality so as to allow duplex operation of OPA lasers  300  and  303 , for transmission and reception of optical signals therebetween. 
     As best seen at an enlargement  310 , OPA laser  300  preferably comprises a seed laser  312  and a laser beam splitting and combining subsystem  314 . Splitting and combining subsystem  314  preferably receives an output laser beam from seed laser  312  and splits the output laser beam into a plurality of sub-beams along a corresponding plurality of channels  316 . Here, by way of example only, an output from seed laser  312  is shown to be split into ten sub-beams along ten channels  316  although it is appreciated that splitting and combining subsystem  314  may include a fewer or greater number of channels along which the output of seed laser  312  is split, and typically may include a far greater number of channels such as 32 or more channels. 
     The relative phase of each sub-beam may be individually modulated by a phase modulator  318 , preferably located along each of channels  316 . Each phase modulated sub-beam produced by the splitting and subsequent phase modulation of the output of seed laser  312  preferably propagates towards a collimating lens  319 . The individually collimated, phase modulated sub-beams are subsequently combined, for example at a focal lens  320 , to form an output beam  322 . 
     Splitting and combining subsystem  314  may also provide laser amplification of the sub-beams, preferably following the splitting of the output beam of seed laser  312  into sub-beams and prior to the combining of the sub-beams to form output beam  322 . Here, by way of example, splitting and combining subsystem  314  is shown to include a plurality of optical amplifiers  324  located along corresponding ones of channels  316  for amplifying each sub-beam. It is appreciated, however, that such amplification is optional and may be omitted, depending on the power output requirements of OPA laser  300 . 
     The phase of output beam  322 , and hence the position and shape of the far-field intensity pattern thereof, is controlled, at least in part, by the relative phases of the constituent sub-beams combined to form output beam  322 . In many applications, such as free space optical communications as illustrated in  FIG.  3 A , it is desirable to dynamically move and shape the far-field intensity pattern of the output beam. This may be achieved in laser system  300  by laser splitting and combining subsystem  314  dynamically varying the relative phases of the individual sub-beams and thereby varying the phase of the combined laser output  322  so as dynamically to control the position and shape of the far-field intensity pattern thereof. 
     The relative phases of the sub-beams are preferably predetermined in accordance with a desired laser output pattern for transmission to receiver  303 . Particularly preferably, the varying relative phases are applied by a phase control subsystem  330 . Phase control subsystem  330  preferably forms a part of a control electronics module  332  in OPA laser  300  and preferably controls each phase modulator  318  so as to dynamically modulate the relative phases of the sub-beams along channels  316 . 
     Due to noise inherent in OPA system  300 , output beam  322  has noise. Noise in output beam  322  is typically phase noise created by thermal or mechanical effects and/or by the amplification process in the case that optical amplifiers  324  are present in OPA system  300 . It is a particular feature of a preferred embodiment of the present invention that laser system  300  includes a noise cancellation subsystem  340  operative to provide a noise cancellation phase correction output in order to cancel out the noise in output beam  322  in a manner detailed henceforth. 
     Particularly preferably, noise cancellation subsystem  340  employs an algorithm to sense and correct phase noise in the combined laser output. The noise cancellation phase correction output is preferably provided by noise cancellation subsystem  340  to phase modulator  318  so as to correct phase noise in output beam  322  and thus avoid distortion of the shape and position of the far field intensity pattern of output beam  322  that would otherwise be caused by the noise. Noise cancellation subsystem  340  may be included in control electronics module  332 . 
     It is understood that output beam  322  may be additionally or alternatively affected by types of noise other than phase noise, including intensity noise. In the case of output beam  322  having intensity noise, noise cancellation subsystem  340  may be operative to provide a noise cancellation phase correction output in order to cancel out the intensity noise in output beam  322 . In such a case, OPA laser system  300  may optionally additionally include intensity modulators  342  along channels  316  for modulating the intensity of each of the sub-beams along channels  316 . 
     It is understood that output beam  322  may be additionally or alternatively affected by mechanical noise which may affect the relative position of the sub-beams. In the case of output beam  322  having position noise, noise cancellation subsystem  340  may be operative to provide a noise cancellation phase correction output in order to cancel out the position noise in output beam  322 . In such a case, OPA laser system  300  may optionally additionally include position modulators  344  along channels  316  for modulating the position of each of the sub-beams along channels  316 . 
     In order to facilitate application of phase variation and noise correction to output beam  322 , a portion of the output of OPA laser  300  is preferably extracted and directed towards at least one detector, here illustrated as a single detector  350 . Detector  350  may alternatively be embodied as multiple detectors, as detailed henceforth with reference to  FIGS.  6 - 8  and  15 - 21   . The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required noise correction and/or phase variation may be calculated. In the embodiment shown in  FIG.  3 A , plurality of sub-beams along channels  316  are directed towards a beam splitter  360 . Beam splitter  360  preferably splits each sub-beam into a transmitted portion  362  and a reflected portion  364  in accordance with a predetermined ratio. For example, beam splitter  360  may split each sub-beam with a 99.9% transmitted: 0.01% reflected ratio. 
     The transmitted portion  362  of the sub-beams preferably propagates towards focal lens  320 , at which focal lens  320  the sub-beams are combined to form output beam  322  having a far-field intensity pattern  366 . The reflected portion  364  of the sub-beams is preferably reflected towards an additional focal lens  368 , at which additional focal lens  368  the sub-beams are combined to form an output reference beam  370  having a far-field intensity pattern  372  incident on a surface of detector  350 . 
     It is understood that the particular structure and configuration of beam splitting and recombining elements shown herein, including beam splitter  360  and focal lenses  320  and  368 , is exemplary only and depicted in a highly simplified form. It is appreciated that OPA laser system  300  may include a variety of such elements, as well as additional optical elements, including, by way of example only, additional or alternative lenses, optical fibers and coherent free-space far-field combiners. 
     As described hereinabove, the shape and position of far-field intensity pattern  366  of the output beam  322  and correspondingly of far-field intensity pattern  372  of the reference beam  370  are constantly changing, due to the ongoing variation of the relative phases of the sub-beams. As a result, far-field intensity pattern  372  is not fixed upon detector  350  but rather is constantly being moved around with respect to detector  350  depending on the combined relative phases of the constituent sub-beams. However, in order for detector  350  to provide the required noise cancellation phase correction output, far-field intensity pattern  372  must be incident upon detector  350  in order for detector to measure the intensity of far-field intensity pattern  372  and hence apply a noise correction accordingly, resulting in a fixed output beam. 
     The conflict between the dynamic nature of far-field intensity pattern  372  due to the phase-variation thereof and the fixed nature required of far-field intensity pattern  372  in order to derive and apply noise correction thereto, is advantageously resolved in the present invention by providing the noise cancellation and phase variation at mutually different times and rates. 
     The noise cancellation phase correction output is provided based on taking into consideration noise measured at detector  350  at a noise sampling rate. The output beam  322  is controlled in such a way that the far-field intensity pattern  372  is incident upon detector  350  during the course of the dynamic changes to the shape and position of output and reference far-field intensity patterns  366  and  372  at a rate that is equal to or higher than the required noise sampling rate. The noise in reference beam  370  is taken into consideration during those intermittent times at which the far-field intensity pattern  372  is returned to detector  350 . 
     At time interstices between the intermittent times at which far-field intensity pattern  372  is incident upon detector  350 , the phase of the combined output beams  322 ,  370  is varied in order to dynamically change the shape and position of the far-field intensity pattern thereof as required to perform additive manufacturing of item  206 . The combined laser output is varied at a phase varying rate which exceeds the noise sampling rate, in order to rapidly change the phase and hence shape and position of the far-field intensity pattern. By way of example, the noise sampling rate may be of the order of 10-1000 Hz whereas the phase varying rate may be greater than 10,000 Hz. 
     The different rates and time scales over which the noise cancellation and phase variation are preferably performed in embodiments of the present invention may be best understood with reference to a graph  380  seen in  FIG.  3 A  and an enlarged version thereof shown in  FIG.  3 B . 
     As seen most clearly in  FIG.  3 B , graph  380  includes an upper portion  382  displaying variation in intensity over time of far-field intensity pattern  372  as measured at detector  350  and a lower portion  384 , displaying variation over the same time period of the relative phases of a number of sub-beams contributing to output beam  322  and reference beam  370 . For the sake of simplicity, the relative phases of ten sub-beams are displayed in graph  380 , although it is appreciated that OPA system  300  and hence the explanation provided herein is applicable to a fewer or, more typically, a far greater number of sub-beams. 
     As seen in upper portion  382 , intensity peaks  386  represent measured intensity of the reference beam  370  when the far field intensity pattern  372  passes over detector  350 . As seen in lower portion  384 , intensity peaks  386  occur at intermittent times T i  at which the relative phase of each sub-beam is zero, meaning that there is no shift in phase between the sub-beams, the position of the combined output beam is therefore not being changed and the far field intensity pattern  372  is hence directly incident on the detector  350 . It is understood that detector  350  may alternatively be positioned such that the relative phase of the sub-beams thereat is non-zero. Furthermore, more than a single detector may be employed so as to allow measurement of the far field intensity pattern  372  at more than one location therealong, as detailed henceforth with reference to  FIGS.  6 - 8  and  15 - 21   . 
     Between intensity peaks  386  the measured intensity is close to zero, as the far-field intensity pattern  372  is moved to the either side of detector  350  and thus is not directly incident on the detector  350 . As appreciated from consideration of upper portion  382 , the magnitude of intensity peaks  386  is not constant due to the presence of noise in the laser output beam, which noise degrades the far field intensity pattern  372 . 
     As seen in lower portion  384 , the relative phases of the sub-beams are varied at time interstices T between  between intermittent times T i . In the phase variation function illustrated herein, the relative phases of the sub-beams are shown to be varied in a periodic, regularly repeating pattern, with equal phase shifts being applied in the positive and negative directions. It is appreciated that such a simplistic pattern is illustrative only and that the phase variation is not necessarily regularly repeating, nor necessarily symmetrical in positive and negative directions. Furthermore, it is understood that time interstices T between  preferably but not necessarily do not overlap with intermittent times T i . Additionally, it is appreciated that at least one of the phase varying rate and the noise sampling rate may be constant or may change over time. 
     Noise cancellation subsystem  340  preferably operates by taking into consideration the noise at intermittent times T i  and providing a noise cancellation phase correction output based on the noise sensed at intermittent times Noise cancellation subsystem  340  preferably employs an algorithm in order to sense noise and correct for the sensed noise accordingly. 
     According to one exemplary embodiment of the present invention, noise cancellation subsystem  340  employs an algorithm in which the relative phase of one channel is changed in such a way that the relative phase is modified by a given phase change Δφ during each cycle of travel of the far-field intensity pattern  372  with respect to detector  350 . Following a number of such cycles, in which a different phase change Δφ is applied to the selected sub-beam over each cycle, the algorithm ascertains the maximum output intensity over all of the cycles and finds the optimum phase change Δ T  that produced this maximum intensity. The phase change of the selected sub-beam is then fixed at the optimum phase change Δφ for subsequent cycles and the algorithm proceeds to optimize another sub-beam. 
     Graph  380  illustrates noise cancellation according to this exemplary algorithm in three sub-beams or channels A, B and C of the total of 10 sub-beams. Sub-beams A, B and C are displayed alone in  FIG.  3 C  for the sake of clarity. It is appreciated that the line style of the traces representing phase variation and noise correction of sub-beams A, B and C respectively is modified in  FIG.  3 C  in comparison to  FIGS.  3 A and  3 B , in order to aid differentiation between the various sub-beams for the purposes of the explanation hereinbelow. 
     As seen initially in the case of channel A, and appreciated most clearly from consideration of an enlargement  390 , the dashed trace represents the pattern of variation in relative phase of sub-beam A, as would be applied by phase control sub-system  330  in the absence of any noise correction. This trace may be termed A uncorrected . The dotted- and dashed trace represents the actual relative phase of sub-beam A as modified by the noise correction algorithm in order to find the optimum phase noise correction. This trace may be termed A corrected . The modified relative phase of A corrected  is shifted with respect to the non-modified relative phase of A uncorrected  by a different Δφ A  over the first five cycles of sub-beam A. The intensity  386  measured at detector  350  varies over the first five cycles of optimization of sub-beam A due to the deliberate change in relative phase shift. 
     Following the first five cycles of sub-beam A, the algorithm ascertains the maximum intensity and finds the phase change Δφ A  that produces the maximum intensity. In this case, the maximum intensity is seen to be IA max  produced by the second phase shift Δφ A . The phase change applied to relative phase variation of sub-beam A is thus fixed at the second phase shift Δφ A  for subsequent cycles and the algorithm proceeds to optimize sub-beam B. 
     It is appreciated that during the sequential cycles of optimization of sub-beam A, the relative phases of the remainder of the sub-beams are varied as usual, each at a phase varying rate that far exceeds the noise sampling rate at which the noise in sub-beam A is taken into consideration. 
     As seen further in the case of sub-beam B, and appreciated most clearly from consideration of an enlargement  392 , the thicker trace during optimization of channel B represents the pattern of variation in relative phase of sub-beam B, as would be applied by phase control sub-system  330  in the absence of any noise correction. This trace may be termed B uncorrected . The thinner trace during optimization of channel B represents the actual relative phase of sub-beam B as modified by the noise correction algorithm in order to find the optimum phase noise correction. This trace may be termed B corrected . The modified relative phase of B corrected  is shifted with respect to the non-modified relative phase of B uncorrected  by a different Δφ B  over five cycles of optimization sub-beam B. The intensity  386  measured at detector  350  varies over these five cycles of optimization sub-beam B due to the deliberate change in relative phase shift. 
     Following these five cycles of sub-beam B, the algorithm ascertains the maximum intensity and finds the phase change Δφ B  that produces the maximum intensity. In this case, the maximum intensity is seen to be IAB max  produced by the fourth phase shift Δφ B . The phase change applied to relative phase variation of sub-beam B is then fixed at the fourth phase shift Δφ B  for subsequent cycles and the algorithm proceeds to optimize sub-beam C. 
     It is appreciated that during the five cycles of optimization of sub-beam B, the relative phases of the remainder of the sub-beams are varied as usual, each at a phase varying rate that far exceeds the noise sampling rate at which the noise in sub-beam B is taken into consideration. 
     A similar optimization process is preferably implemented for sub-beam C, in which a phase change Δφ C  is applied over several cycles in order to optimize the output beam intensity and correct for intensity degradation thereof due to phase noise in sub-beam C. 
     Detector  350  may operate continuously in order to continuously optimize the relative phases of the sub-beams and correct for phase noise therein. However, due to a finite response time of detector  350 , detector  350  only takes into consideration the noise in reference beam  370  at intermittent times, at a relatively slow noise sampling rate. The noise sampling rate is preferably but not necessarily predetermined. The noise sampling rate may alternatively be random. 
     It is appreciated that the particular parameters of the noise correction algorithm depicted in graph  380  are exemplary only and may be readily modified, as will be understood by one skilled in the art. For example, the phase shift Δφ may be optimized over a greater or fewer number of cycles than illustrated herein, each sub-beam may be fully optimized each time the sub-beam passes over detector  350  or several sub-beams or all of the sub-beams may be optimized during each cycle in which the far-field intensity pattern passes over detector  350 . Furthermore, non-sequential noise correction optimization algorithms may alternatively be implemented, including, but not limited to, Stochastic parallel gradient descent optimization algorithms. 
     The use of dynamically shaped, noise corrected optical phased array output beams for free-space optical communication is highly advantageous and enables rapid beam steering, fast power modulation, fast beam focusing and beam shape tailoring. Both the speed and quality of communication are improved using dynamically shaped, noise corrected optical phase array output in comparison to conventional free space optical communication methods. It is appreciated that but for the provision of noise correction, in accordance with preferred embodiments of the present invention, the shape and position of the optical phased array output beam would be degraded, thereby degrading the quality, speed and precision of the transmitted laser output. 
     In order to maintain output beam intensity as the far-field intensity pattern of the beam moves, as is advantageous in certain optical communication applications, movement of the output beam may be controlled such that the beam spends more time at lower-intensity positions so as to compensate for reduced power delivery thereat. Additionally or alternatively, an intensity profile mask such as an ND filter may be applied to the output beam in order to modify the intensity thereof. 
     Reference is now made to  FIG.  4 A , which is a simplified schematic illustration of an optical phased array laser system for noise corrected dynamic beam shaping, constructed and operative in accordance with yet another preferred embodiment of the present invention; and to  FIGS.  4 B and  4 C , which are simplified graphical representations of phase variation and noise correction in a system of the type illustrated in  FIG.  4 A . 
     As seen in  FIG.  4 A , there is provided an optical phased array (OPA) laser system  400 , here shown to be employed, by way of example, within a laser welding system  402 . Laser welding system  402  may include OPA laser system  400  mounted on or within a portion of a laser welding robot  404 . An item, such as an item  406 , may be welded by laser welding robot  404 , as is detailed henceforth. It is understood that although laser welding system  402  is illustrated herein in the context of welding robot  404 , system  402  may be adapted for use in any welding setup, as will be appreciated by one skilled in the art. 
     As best seen at an enlargement  410 , OPA laser  400  preferably comprises a seed laser  412  and a laser beam splitting and combining subsystem  414 . Splitting and combining subsystem  414  preferably receives an output laser beam from seed laser  412  and splits the output laser beam into a plurality of sub-beams along a corresponding plurality of channels  416 . Here, by way of example only, an output from seed laser  412  is shown to be split into ten sub-beams along ten channels  416  although it is appreciated that splitting and combining subsystem  414  may include a fewer or greater number of channels along which the output of seed laser  412  is split, and typically may include a far greater number of channels such as 32 or more channels. 
     The relative phase of each sub-beam may be individually modulated by a phase modulator  418 , preferably located along each of channels  416 . Each phase modulated sub-beam produced by the splitting and subsequent phase modulation of the output of seed laser  412  preferably propagates towards a collimating lens  419 . The individually collimated, phase modulated sub-beams are subsequently combined, for example at a focal lens  420 , to form an output beam  422 . 
     Splitting and combining subsystem  414  may also provide laser amplification of the sub-beams, preferably following the splitting of the output beam of seed laser  412  into sub-beams and prior to the combining of the sub-beams to form output beam  422 . Here, by way of example, splitting and combining subsystem  414  is shown to include a plurality of optical amplifiers  424  located along corresponding ones of channels  416  for amplifying each sub-beam. It is appreciated, however, that such amplification is optional and may be omitted, depending on the power output requirements of OPA laser  400 . 
     The phase of output beam  422 , and hence the position and shape of the far-field intensity pattern thereof, is controlled, at least in part, by the relative phases of the constituent sub-beams combined to form output beam  422 . In many applications, such as laser welding as illustrated in  FIG.  4 A , it is desirable to dynamically move and shape the far-field intensity pattern of the output beam. This may be achieved in laser system  400  by laser splitting and combining subsystem  414  dynamically varying the relative phases of the individual sub-beams and thereby varying the phase of the combined laser output  422  so as dynamically to control the position and shape of the far-field intensity pattern thereof. 
     The relative phases of the sub-beams are preferably predetermined in accordance with the desired laser output pattern for the welding of item  406 . Particularly preferably, the varying relative phases are applied by a phase control subsystem  430 . Phase control subsystem  430  preferably forms a part of a control electronics module  432  in OPA laser  400  and preferably controls each phase modulator  418  so as to dynamically modulate the relative phases of the sub-beams along channels  416 . 
     Due to noise inherent in OPA system  400 , output beam  422  has noise. Noise in output beam  422  is typically phase noise created by thermal or mechanical effects and/or by the amplification process in the case that optical amplifiers  424  are present in OPA system  400 . It is a particular feature of a preferred embodiment of the present invention that laser system  400  includes a noise cancellation subsystem  440  operative to provide a noise cancellation phase correction output in order to cancel out the noise in output beam  422  in a manner detailed henceforth. 
     Particularly preferably, noise cancellation subsystem  440  employs an algorithm to sense and correct phase noise in the combined laser output. The noise cancellation phase correction output is preferably provided by noise cancellation subsystem  440  to phase modulator  418  so as to correct phase noise in output beam  422  and thus avoid distortion of the shape and position of the far field intensity pattern of output beam  422  that would otherwise be caused by the noise. Noise cancellation subsystem  440  may be included in control electronics module  432 . 
     It is understood that output beam  422  may be additionally or alternatively affected by types of noise other than phase noise, including intensity noise. In the case of output beam  422  having intensity noise, noise cancellation subsystem  440  may be operative to provide a noise cancellation phase correction output in order to cancel out the intensity noise in output beam  422 . In such a case, OPA laser system  400  may optionally additionally include intensity modulators  442  along channels  416  for modulating the intensity of each of the sub-beams along channels  416 . 
     It is understood that output beam  422  may be additionally or alternatively affected by mechanical noise which may affect the relative position of the sub-beams. In the case of output beam  422  having position noise, noise cancellation subsystem  440  may be operative to provide a noise cancellation phase correction output in order to cancel out the position noise in output beam  422 . In such a case, OPA laser system  400  may optionally additionally include position modulators  444  along channels  416  for modulating the position of each of the sub-beams along channels  416 . 
     In order to facilitate application of phase variation and noise correction to output beam  422 , a portion of the output of OPA laser  400  is preferably extracted and directed towards at least one detector, here illustrated as a single detector  450 . Detector  450  may alternatively be embodied as multiple detectors, as detailed henceforth with reference to  FIGS.  6 - 8  and  15 - 21   . The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required noise correction and/or phase variation may be calculated. In the embodiment shown in  FIG.  4 A , plurality of sub-beams along channels  416  are directed towards a beam splitter  460 . Beam splitter  460  preferably splits each sub-beam into a transmitted portion  462  and a reflected portion  464  in accordance with a predetermined ratio. For example, beam splitter  460  may split each sub-beam with a 99.9% transmitted: 0.01% reflected ratio. 
     The transmitted portion  462  of the sub-beams preferably propagates towards focal lens  420 , at which focal lens  420  the sub-beams are combined to form output beam  422  having a far-field intensity pattern  466  incident on item  406 . The reflected portion  464  of the sub-beams is preferably reflected towards an additional focal lens  468 , at which additional focal lens  468  the sub-beams are combined to form an output reference beam  470  having a far-field intensity pattern  472  incident on a surface of detector  450 . 
     It is understood that the particular structure and configuration of beam splitting and recombining elements shown herein, including beam splitter  460  and focal lenses  420  and  468 , is exemplary only and depicted in a highly simplified form. It is appreciated that OPA laser system  400  may include a variety of such elements, as well as additional optical elements, including, by way of example only, additional or alternative lenses, optical fibers and coherent free-space far-field combiners. 
     As described hereinabove, the shape and position of far-field intensity pattern  466  of the output beam  422  and correspondingly of far-field intensity pattern  472  of the reference beam  470  are constantly changing, due to the ongoing variation of the relative phases of the sub-beams. As a result, far-field intensity pattern  472  is not fixed upon detector  450  but rather is constantly being moved around with respect to detector  450  depending on the combined relative phases of the constituent sub-beams. However, in order for detector  450  to provide the required noise cancellation phase correction output, far-field intensity pattern  472  must be incident upon detector  450  in order for detector to measure the intensity of far-field intensity pattern  472  and hence apply a noise correction accordingly, resulting in a fixed output beam. 
     The conflict between the dynamic nature of far-field intensity pattern  472  due to the phase-variation thereof and the fixed nature required of far-field intensity pattern  472  in order to derive and apply noise correction thereto, is advantageously resolved in the present invention by providing the noise cancellation and phase variation at mutually different times and rates. 
     The noise cancellation phase correction output is provided based on taking into consideration noise measured at detector  450  at a noise sampling rate. The output beam  422  is controlled in such a way that the far-field intensity pattern  472  is incident upon detector  450  during the course of the dynamic changes to the shape and position of output and reference far-field intensity patterns  466  and  472  at a rate that is equal to or higher than the required noise sampling rate. The noise in reference beam  470  is taken into consideration during those intermittent times at which the far-field intensity pattern  472  is returned to detector  450 . 
     At time interstices between the intermittent times at which far-field intensity pattern  472  is incident upon detector  450 , the phase of the combined output beams  422 ,  470  is varied in order to dynamically change the shape and position of the far-field intensity pattern thereof as required to perform laser welding of item  406 . The combined laser output is varied at a phase varying rate which exceeds the noise sampling rate, in order to rapidly change the phase and hence shape and position of the far-field intensity pattern. By way of example, the noise sampling rate may be of the order of 10-1000 Hz whereas the phase varying rate may be greater than 10,000 Hz. 
     The different rates and time scales over which the noise cancellation and phase variation are preferably performed in embodiments of the present invention may be best understood with reference to a graph  480  seen in  FIG.  4 A  and an enlarged version thereof shown in  FIG.  4 B . 
     As seen most clearly in  FIG.  4 B , graph  480  includes an upper portion  482  displaying variation in intensity over time of far-field intensity pattern  472  as measured at detector  450  and a lower portion  484 , displaying variation over the same time period of the relative phases of a number of sub-beams contributing to output beam  422  and reference beam  470 . For the sake of simplicity, the relative phases of ten sub-beams are displayed in graph  480 , although it is appreciated that OPA system  400  and hence the explanation provided herein is applicable to a fewer or, more typically, a far greater number of sub-beams. 
     As seen in upper portion  482 , intensity peaks  486  represent measured intensity of the reference beam  470  when the far field intensity pattern  472  passes over detector  450 . As seen in lower portion  484 , intensity peaks  486  occur at intermittent times T i  at which the relative phase of each sub-beam is zero, meaning that there is no shift in phase between the sub-beams, the position of the combined output beam is therefore not being changed and the far field intensity pattern  472  is hence directly incident on the detector  450 . It is understood that detector  450  may alternatively be positioned such that the relative phase of the sub-beams thereat is non-zero. Furthermore, more than a single detector may be employed so as to allow measurement of the far field intensity pattern  472  at more than one location therealong, as detailed henceforth with reference to  FIGS.  6 - 8  and  15 - 21   . 
     Between intensity peaks  486  the measured intensity is close to zero, as the far-field intensity pattern  472  is moved to the either side of detector  450  and thus is not directly incident on the detector  450 . As appreciated from consideration of upper portion  482 , the magnitude of intensity peaks  486  is not constant due to the presence of noise in the laser output beam, which noise degrades the far field intensity pattern  472 . 
     As seen in lower portion  484 , the relative phases of the sub-beams are varied at time interstices T between  between intermittent times T i . In the phase variation function illustrated herein, the relative phases of the sub-beams are shown to be varied in a periodic, regularly repeating pattern, with equal phase shifts being applied in the positive and negative directions. It is appreciated that such a simplistic pattern is illustrative only and that the phase variation is not necessarily regularly repeating, nor necessarily symmetrical in positive and negative directions. Furthermore, it is understood that time interstices T between  preferably but not necessarily do not overlap with intermittent times T i . Additionally, it is appreciated that at least one of the phase varying rate and the noise sampling rate may be constant or may change over time. 
     Noise cancellation subsystem  440  preferably operates by taking into consideration the noise at intermittent times T i  and providing a noise cancellation phase correction output based on the noise sensed at intermittent times T i . Noise cancellation subsystem  440  preferably employs an algorithm in order to sense noise and correct for the sensed noise accordingly. 
     According to one exemplary embodiment of the present invention, noise cancellation subsystem  440  employs an algorithm in which the relative phase of one channel is changed in such a way that the relative phase is modified by a given phase change Δφ during each cycle of travel of the far-field intensity pattern  472  with respect to detector  150 . Following a number of such cycles, in which a different phase change Δφ is applied to the selected sub-beam over each cycle, the algorithm ascertains the maximum output intensity over all of the cycles and finds the optimum phase change Δφ that produced this maximum intensity. The phase change of the selected sub-beam is then fixed at the optimum phase change Δφ for subsequent cycles and the algorithm proceeds to optimize another sub-beam. 
     Graph  480  illustrates noise cancellation according to this exemplary algorithm in three sub-beams or channels A, B and C of the total of 10 sub-beams. Sub-beams A, B and C are displayed alone in  FIG.  4 C  for the sake of clarity. It is appreciated that the line style of the traces representing phase variation and noise correction of sub-beams A, B and C respectively is modified in  FIG.  4 C  in comparison to  FIGS.  4 A and  4 B , in order to aid differentiation between the various sub-beams for the purposes of the explanation hereinbelow. 
     As seen initially in the case of channel A, and appreciated most clearly from consideration of an enlargement  490 , the dashed trace represents the pattern of variation in relative phase of sub-beam A, as would be applied by phase control sub-system  430  in the absence of any noise correction. This trace may be termed A uncorrected . The dotted- and dashed trace represents the actual relative phase of sub-beam A as modified by the noise correction algorithm in order to find the optimum phase noise correction. This trace may be termed A corrected  The modified relative phase of A corrected  is shifted with respect to the non-modified relative phase of A uncorrected  by a different Δφ A  over the first five cycles of sub-beam A. The intensity  486  measured at detector  450  varies over the first five cycles of optimization of sub-beam A due to the deliberate change in relative phase shift. 
     Following the first five cycles of sub-beam A, the algorithm ascertains the maximum intensity and finds the phase change Δφ A  that produces the maximum intensity. In this case, the maximum intensity is seen to be IA max  produced by the second phase shift Δφ A . The phase change applied to relative phase variation of sub-beam A is thus fixed at the second phase shift Δφ A  for subsequent cycles and the algorithm proceeds to optimize sub-beam B. 
     It is appreciated that during the sequential cycles of optimization of sub-beam A, the relative phases of the remainder of the sub-beams are varied as usual, each at a phase varying rate that far exceeds the noise sampling rate at which the noise in sub-beam A is taken into consideration. 
     As seen further in the case of sub-beam B, and appreciated most clearly from consideration of an enlargement  492 , the thicker trace during optimization of channel B represents the pattern of variation in relative phase of sub-beam B, as would be applied by phase control sub-system  430  in the absence of any noise correction. This trace may be termed B uncorrected . The thinner trace during optimization of channel B represents the actual relative phase of sub-beam B as modified by the noise correction algorithm in order to find the optimum phase noise correction. This trace may be termed B corrected . The modified relative phase of B corrected  is shifted with respect to the non-modified relative phase of B uncorrected  by a different Δφ B  over five cycles of optimization sub-beam B. The intensity  486  measured at detector  450  varies over these five cycles of optimization sub-beam B due to the deliberate change in relative phase shift. 
     Following these five cycles of sub-beam B, the algorithm ascertains the maximum intensity and finds the phase change Δφ B  that produces the maximum intensity. In this case, the maximum intensity is seen to be IAB max , produced by the fourth phase shift Δφ B . The phase change applied to relative phase variation of sub-beam B is then fixed at the fourth phase shift Δφ B  for subsequent cycles and the algorithm proceeds to optimize sub-beam C. 
     It is appreciated that during the five cycles of optimization of sub-beam B, the relative phases of the remainder of the sub-beams are varied as usual, each at a phase varying rate that far exceeds the noise sampling rate at which the noise in sub-beam B is taken into consideration. 
     A similar optimization process is preferably implemented for sub-beam C, in which a phase change Δφ C  is applied over several cycles in order to optimize the output beam intensity and correct for intensity degradation thereof due to phase noise in sub-beam C. 
     Detector  450  may operate continuously in order to continuously optimize the relative phases of the sub-beams and correct for phase noise therein. However, due to a finite response time of detector  450 , detector  450  only takes into consideration the noise in reference beam  470  at intermittent times, at a relatively slow noise sampling rate. The noise sampling rate is preferably but not necessarily predetermined. The noise sampling rate may alternatively be random. 
     It is appreciated that the particular parameters of the noise correction algorithm depicted in graph  480  are exemplary only and may be readily modified, as will be understood by one skilled in the art. For example, the phase shift Δφ may be optimized over a greater or fewer number of cycles than illustrated herein, each sub-beam may be fully optimized each time the sub-beam passes over detector  450  or several sub-beams or all of the sub-beams may be optimized during each cycle in which the far-field intensity pattern passes over detector  450 . Furthermore, non-sequential noise correction optimization algorithms may alternatively be implemented, including, but not limited to, Stochastic parallel gradient descent optimization algorithms. 
     The use of dynamically shaped, noise corrected optical phased array output beams for laser welding is highly advantageous and enables rapid beam steering, fast power modulation, fast beam focusing and beam shape tailoring. Both the speed and quality with which a material may be cut are improved using dynamically shaped, noise corrected optical phase array output in comparison to conventional laser cutting methods. It is appreciated that but for the provision of noise correction, in accordance with preferred embodiments of the present invention, the shape and position of the optical phased array output beam would be degraded, thereby degrading the quality, speed and precision of the laser cutting process. 
     In order to maintain output beam intensity as the far-field intensity pattern of the beam moves, as is advantageous in certain laser cutting applications, movement of the output beam may be controlled such that the beam spends more time at lower-intensity positions so as to compensate for reduced power delivery thereat. Additionally or alternatively, an intensity profile mask such as an ND filter may be applied to the output beam in order to modify the intensity thereof. 
     Reference is now made to  FIGS.  5 A- 5 G , which are simplified illustrations of possible far-field motion of an output of an optical phased array laser system of the types illustrated in  FIGS.  1 A- 4 C . 
     As detailed hereinabove, the use of dynamically shaped, noise corrected optical phased array output beams in various laser applications, including but not limited to laser cutting, laser additive manufacturing, laser welding and laser free-space optical communication, is highly advantageous and enables rapid beam steering, fast power modulation, fast beam focusing and beam shape tailoring. Exemplary far-field patterns illustrating rapid beam steering in accordance with embodiments of the present invention are shown in  FIGS.  5 A and  5 B . These beam steering patterns may be provided in combination with and so as to compliment mechanical spatial modulation of the beam, such as mechanical beam steering. Mechanical beam steering may be due to motion provided by positioning table  104  shown in  FIG.  1 A ; due to mirror scanning, such as in an additive manufacturing system of the type shown in  FIG.  2 A ; due to mechanical motion between laser system  300  and receiver  303  shown in  FIG.  3 A ; due to motion provide by robot  404  shown in  FIG.  4 A , or due to any other source of mechanical motion. 
     The mechanical motion may be desired or undesired motion. Preferably, the far-field rapid beam steering provided by embodiments of the present invention compliments the mechanical motion so as to achieve the desired combined beam motion. The desired combined motion may be faster and/or more precise than would be produced as a result of mechanical beam modulation alone. 
     As seen in  FIG.  5 A , dynamically shaped, noise corrected optical phased array output beams may exhibit rapid multipoint jumping, as illustrated by first beam paths  502 , which rapid multipoint jumping compliments beam motion due to mechanical scanning, represented by a second beam path  504 . 
     By way of example, such multipoint jumping may be advantageous in material processing, wherein time is taken for energy to be absorbed at each point of the material being processed. Multipoint jumping allows the beam to jump between points, returning to each point multiple times, thus facilitating the processing of many points in parallel. Further by way of example, such multipoint jumping may be advantageous in communication systems by allowing transmission to multiple locations in parallel. 
     As seen in  FIG.  5 B , the use of dynamically shaped, noise corrected optical phased array output beams also facilitates rapid scanning, as illustrated by a third beam path  506 , which rapid scanning compliments beam motion due to mechanical scanning represented by a fourth beam path  508 . Such rapid scanning facilitates continuous, smooth mechanical beam motion, fine features of which may be provided by far-field dynamic shaping in accordance with embodiments of the present invention. Furthermore, dynamic noise corrected far field modulation may be provided in combination with mechanical beam motion in order to correct inaccuracies that may be present in the mechanically modulated beam patterns. 
     An exemplary far field beam pattern illustrating electro-optical beam wobble in accordance with preferred embodiments of the present invention is shown in  FIG.  5 C . As seen in  FIG.  5 C , the dynamically shaped, noise corrected optical phased array output beam is controlled so as to exhibit a rapid beam wobble  510  along a direction of beam motion  512 , particularly useful, for example, in a laser welding system such as that illustrated in  FIG.  4 A . 
     Exemplary far-field beam patterns illustrating dynamic modification of depth of focus in accordance with preferred embodiments of the present invention are shown in  FIGS.  5 D- 5 F . As seen in  FIGS.  5 D- 5 F , the depth of the beam focus may be dynamically changed by systems of the present invention, allowing variable beam focal length for scanning ( FIG.  5 E ) and for deep cutting ( FIGS.  5 D and  5 F ), particularly useful, for example, in cutting, additive manufacturing and welding systems of the types illustrated in  FIGS.  1 A,  2 A and  4 A . 
     Exemplary far-field beam patterns illustrating dynamic beam shaping in accordance with preferred embodiments of the present invention are shown in  FIG.  5 G . As seen in  FIG.  5 G , the shape of the beam may be dynamically changed to create a desired beam shape output. This may be particularly useful, for example, in cutting, additive manufacturing and welding systems of the types illustrated in  FIGS.  1 A,  2 A and  4 A , as well as in other contexts. As is well known in the art, the quality and speed of laser cutting, welding and 3D printing are typically influenced by beam size and shape. The present invention allows dynamic adaptation of the beam to the optimum shape at any point. 
     It is appreciated that the various far-field beam motion patterns illustrated in  FIGS.  5 A- 5 G  are all preferably produced by systems of the present invention using digital electronic controls and without requiring any moving parts. 
     Reference is now made to  FIG.  6   , which is a simplified schematic illustration of an optical phased array laser system including multiple detectors and corresponding multiple closely spaced optical pathways, constructed and operative in accordance with a preferred embodiment of the present invention. 
     As seen in  FIG.  6   , there is provided an optical phased array (OPA) laser  600 . OPA laser  600  may be generally of the type shown in any of  FIGS.  1 A- 4 C  and preferably includes a seed laser  612  and a laser beam splitting and combining subsystem  614 . Splitting and combining subsystem  614  preferably receives an output laser beam from seed laser  612  and splits the output laser beam into a plurality of sub-beams along a corresponding plurality of channels  616 . Here, by way of example only, an output from seed laser  612  is shown to be split into four sub-beams along four channels  616  although it is appreciated that splitting and combining subsystem  614  may include a fewer or greater number of channels along which the output of seed laser  612  is split, and typically may include a far greater number of channels such as 32 or more channels. 
     The relative phase of each sub-beam may be individually modulated by a phase modulator  618 , preferably located along each of channels  616 . Each phase modulated sub-beam produced by the splitting and subsequent phase modulation of the output of seed laser  612  preferably propagates towards a collimating lens  619 . The individually collimated, phase modulated sub-beams are subsequently combined, for example at a focal lens  620 , to form an output beam  622 . 
     Splitting and combining subsystem  614  may also provide laser amplification of the sub-beams, preferably following the splitting of the output beam of seed laser  612  into sub-beams and prior to the combining of the sub-beams to form output beam  622 . Here, by way of example, splitting and combining subsystem  614  is shown to include a plurality of optical amplifiers  624  located along corresponding ones of channels  616  for amplifying each sub-beam. It is appreciated, however, that such amplification is optional and may be omitted, depending on the power output specifications of OPA laser  600 . 
     The phase of output beam  622 , and hence the position and shape of the far-field intensity pattern thereof, is controlled, at least in part, by the relative phases of the constituent sub-beams combined to form output beam  622 . As described hereinabove with reference to  FIGS.  1 A- 5 G , in many applications, such as laser cutting, laser welding, laser additive manufacturing and optical free space communications, it is desirable to dynamically move and shape the far-field intensity pattern of the output beam. This may be achieved in laser system  600  by laser splitting and combining subsystem  614  dynamically varying the relative phases of the individual sub-beams and thereby varying the phase of the combined laser output  622  so as dynamically to control the position and shape of the far-field intensity pattern thereof. 
     The relative phases of the sub-beams are preferably predetermined in accordance with the desired laser output pattern. Particularly preferably, the varying relative phases are applied by a phase control subsystem  630 . Phase control subsystem  630  preferably forms a part of a control electronics module  632  in OPA laser  600  and preferably controls each phase modulator  618  so as to dynamically modulate the relative phases of the sub-beams along channels  616 , as described hereinabove with reference to phase control subsystem  130 ,  230 ,  330 ,  430  of  FIGS.  1 A,  2 A,  3 A and  4 A  respectively. 
     Due to noise inherent in OPA system  600 , output beam  622  has noise. Noise in output beam  622  is typically phase noise created by thermal or mechanical effects and/or by the amplification process in the case that optical amplifiers  624  are present in OPA system  600 . OPA system  600  preferably includes a noise cancellation subsystem  640  operative to provide a noise cancellation phase correction output in order to cancel out the noise in output beam  622  in a manner detailed henceforth. 
     Particularly preferably, noise cancellation subsystem  640  employs an algorithm to sense and correct phase noise in the combined laser output, preferably, although not necessarily, of the type described hereinabove with reference to  FIGS.  1 A- 4 C . The noise cancellation phase correction output is preferably provided by noise cancellation subsystem  640  to phase modulators  618  so as to correct phase noise in output beam  622  and thus avoid distortion of the shape and position of the far field intensity pattern of output beam  622  that would otherwise be caused by the noise. Noise cancellation subsystem  640  may be included in control electronics module  632 . 
     In order to facilitate application of phase variation and noise correction to output beam  622 , a portion of the output of OPA laser  600  is preferably extracted and directed towards a plurality of detectors  650 . The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required noise correction and/or phase variation may be calculated. 
     In accordance with a preferred embodiment of the present invention, plurality of sub-beams along channels  616  are directed towards a beam splitter  660 . Beam splitter  660  preferably splits each sub-beam into a transmitted portion  662  and a reflected portion  664  in accordance with a predetermined ratio. For example, beam splitter  660  may split each sub-beam with a 99.9% transmitted: 0.01% reflected ratio. 
     The transmitted portion  662  of the sub-beams preferably propagates towards focal lens  620 , at which focal lens  620  the sub-beams are combined to form output beam  622  having a far-field intensity pattern  666 . The reflected portion  664  of the sub-beams is preferably reflected towards an additional focal lens  668 , at which additional focal lens  668  the sub-beams are combined to form an output reference beam  670  having a far-field intensity pattern  672  incident on a surface of one or more of plurality of detectors  650 . 
     As described hereinabove with reference to  FIGS.  1 A- 4 C , the noise cancellation phase correction output is preferably provided based on taking into consideration noise measured at detectors  650  at a noise sampling rate. The output beam  622  is controlled in such a way that the far-field intensity pattern  672  is incident upon detectors  650  during the course of the dynamic changes to the shape and position of output and reference far-field intensity patterns  666 ,  672  at a rate that is equal to or higher than the required noise sampling rate. The noise in reference beam  670  is taken into consideration during those intermittent times at which the far-field intensity pattern  672  is returned to detectors  650 . 
     At time interstices between the intermittent times at which far-field intensity pattern  672  is incident upon detectors  650 , the phase of the combined output beams  622 ,  670  is varied in order to dynamically change the shape and position of the far-field intensity pattern thereof. The combined laser output is varied at a phase varying rate which exceeds the noise sampling rate, in order to rapidly change the phase and hence shape and position of the far-field intensity pattern. The noise cancellation and phase variation are thus preferably provided at mutually different times and rates. 
     The use of a plurality of detectors  650 , rather than a single detector, has been found to be highly advantageous in certain embodiments of the present invention, giving rise to various advantages detailed henceforth. However, in the case of the focal length of additional focal lens  668  being relatively short, as is desirable in order for system  600  to be formed in a compact manner, ones of plurality of detectors  650  would preferably be required to be positioned very close to one another. The desirable inter-detector spacing may be of the order of several microns. Such a high spatial density arrangement of detectors  650  is typically impractical, particularly in the case of conventional detectors having dimensions far greater than the preferred inter-detector spacing. 
     In order to allow high spatial density sampling of far-field intensity pattern  672  by plurality of detectors  650 , OPA system  600  preferably includes a plurality of optical pathways, here embodied by way of example as a plurality of optical fibers  680 , correspondingly coupled to plurality of detectors  650 . Reference beam  670  preferably enters one or more of a plurality of open ends  682  of optical fibers  680  and travels therealong to corresponding ones of detectors  650 . Plurality of ends  682  of plurality of optical fibers  680  is preferably arranged so as to have a spatial density greater than a spatial density of plurality of detectors  650 , meaning that the spacing between open ends  682  of adjacent ones of optical fibers  680  is smaller than the spacing between corresponding adjacent ones of detectors  650 . This allows detectors  650  to detect far-field intensity pattern  672  at closely spaced intervals therealong, without detectors  650  being required to be themselves physically located at those closely spaced positions at which the far-field intensity pattern  672  is sampled. 
     By way of example, ends  682  of optical fibers  680  may be interspaced by a distance of several microns, whereas detectors  650  coupled to corresponding ones of optical fibers  680  may be interspaced by a distance of several millimeters. It is appreciated that such an arrangement allows the use of conventional detectors in system  600 , and obviates the need for expensive and complex miniaturized detection systems. 
     The inclusion of a plurality of detectors  650 , effectively closely spaced as facilitated by the actual physical close spacing of ends  682  of optical fibers  680 , has been found to be highly advantageous in preferred embodiments of the present invention. In particular, the use of a plurality of detectors  650  rather than only a single detector  150 , as shown in  FIGS.  1 A,  2 A,  3 A and  4 A , allows the far-field intensity pattern  672  to be sampled at a plurality of locations rather than at only a single location. This facilitates more efficient and/or more frequent noise correction during the dynamic variation of output beam  622 . 
     It is appreciated that the plurality of closely spaced optical pathways is not limited to being embodied as a plurality of optical fibers  680  having ends  682  very closely interspaced, with an inter-fiber end spacing of less than the inter-detector spacing of detectors  650 . Rather, the scope of the present invention extends to include any suitable plurality of optical pathways that may deliver therealong far-field intensity reference pattern  672  to plurality of detectors  650 , and may be arranged with a sufficiently great spatial density. 
     By way of example, the plurality of closely spaced optical pathways may be embodied as a plurality of lenses  780  as illustrated in  FIG.  7   . Plurality of lenses  780  may be very closely spaced so as to focus portions of far-field intensity reference pattern  672  towards plurality of less closely spaced detectors  650 . Further by way of example, the plurality of closely spaced optical pathways may be embodied as a plurality of mirrors  880  operating in cooperation with a corresponding plurality of lenses  882  as illustrated in  FIG.  8   . Plurality of mirrors  880  may be very closely spaced so as to reflect portions of far-field intensity reference pattern  672  towards plurality of less closely spaced detectors  650 . 
     It is appreciated that an OPA laser system of the type shown in any of  FIGS.  6 - 8   , including multiple detectors, may be incorporated in an OPA laser system of the type shown in any of  FIGS.  1 A,  2 A,  3 A and  4 A  in order to provide more efficient and/or more frequent noise correction to the phase-varied output thereof. 
     Reference is now made to  FIG.  9   , which is a simplified schematic illustration of an optical phased array laser system including a detector mask configured in accordance with an exemplary laser beam trajectory, constructed and operative in accordance with a preferred embodiment of the present invention. 
     As seen in  FIG.  9   , there is provided an optical phased array (OPA) laser  900 . OPA laser  900  may generally resemble OPA laser  600  of  FIG.  6    in relevant aspects thereof, with the exception of the detector arrangement employed therein. Whereas OPA laser  600  preferably employs multiple detectors receiving an output beam by way of corresponding multiple closely spaced optical pathways, OPA laser  900  does not necessarily employ more than one detector. 
     It is particular feature of a preferred embodiment of the present invention illustrated in  FIG.  9    that OPA laser  900  preferably includes an optical mask  980  having at least one transmissive region  982  for providing therethrough output reference beam  670  to at least one detector  650 , here illustrated to comprise a single detector  650 . Optical mask  980  is preferably an optically opaque element transmissive to beam  670  only in transmissive region  982 . Here, by way of example, transmissive region  982  is shown to be formed as a star-shaped transmissive path, configured in accordance with a star-shaped trajectory of output and reference far-field intensity patterns  666 ,  672 . 
     Output reference beam  670  is preferably transmitted through transmissive region  982  and focused on detector  650  by way of a focusing subsystem, here embodied by way of example, as a focusing lens  990 . A noise cancellation phase correction output is preferably provided by noise cancellation subsystem  630  based on taking into consideration the intensity of far-field intensity pattern  672  focused and incident upon detector  650 . 
     More specifically, the phases of output and reference beams  622 ,  670  are preferably dynamically varied by phase control subsystem  630  so as to cause output and reference beams  622  and  670  to traverse a predetermined trajectory, such as a star-shaped trajectory corresponding to the shape of star-shaped transmissive region  982 . In the absence of noise in OPA laser  900 , the trajectory traversed by output and reference beams  622  and  670  would at least nearly exactly correspond to the shape of transmissive region  982 , such that an intensity of far-field intensity pattern  672  as detected by detector  650  would be a maximal, non-degraded intensity. However, due to the presence of noise in output and reference beams  622  and  670 , a trajectory and shape of far-field intensity pattern  672  may somewhat deviate from the shape of transmissive region  982 , such that a portion of reference beam  670  is incident upon opaque regions of mask  980  rather than on transmissive region  982 , and thus not transmitted to detector  650  through transmissive region  982 . In such a case, the intensity of far-field intensity pattern  672  as detected by detector  650  is lower than the maximal intensity that would be detected in the absence of noise. 
     The degradation in intensity of far-field intensity pattern  672  as measured by detector  650  is thus preferably indicative of the noise-resultant distortion of the trajectory of output and reference beams  622 ,  670  and thereby may be used to derive the required noise cancellation phase correction output, to be applied by noise cancellation subsystem  640 . 
     It is appreciated that the above-described arrangement of detector  650  positioned behind mask  980  allows only a single detector  650  to be employed in order to sense the output intensity of reference beam  670  along a trajectory thereof, based on which a noise cancellation phase correction output may be applied. This is contrast to alternative detector arrangements not including mask  980 , such as those described hereinabove with reference to  FIGS.  6 - 8   , in which multiple detectors may be employed in order to provide sufficiently efficient and/or frequent noise correction during the dynamic variation of output beam  622 . 
     In addition to the variation of intensity of reference beam  670  as measured by detector  650  due to the distortion of the beam trajectory due to noise, the intensity of reference beam  670  typically may vary along the trajectory thereof, due to inherent intensity variations in far-field intensity pattern  672 . This may complicate the noise correction feedback provided by detector  650 , since variations in intensity of reference beam  670  may be attributable to noise or to inherent intensity variations not related to noise. 
     In order to improve the reliability of the noise correction feedback provided by detector  650 , transmissive region  982  of mask  980  may be provided with regions of varying transparency, the transparency levels of which are set so as to compensate for inherent intensity variations in reference beam  670  along the trajectory thereof. 
     A highly simplified representation of transmissive region  982  of mask  980  having non-uniform transparency is shown in  FIG.  10   . As seen in  FIG.  10   , a first portion of transmissive region  982  defined between a first point P 1  and a second point P 2  thereof may have a first transparency T 1 ; a second portion of transmissive region  982  defined between second point P 2  and a third point P 3  may have a second transparency T 2 , different from first transparency T 1 ; a third portion of transmissive region  982  defined between third point P 3  and a fourth point P 4  may have first transparency T 1 ; a fourth portion of transmissive region  982  defined between fourth point P 4  and a fifth point P 5  may have a third transparency T 3 , different from first and second transparencies T 1  and T 2 ; and a fifth point of transmissive region  982  defined between fifth point P 5  and first point P 1  may have second transparency T 2 . 
     It is appreciated that various portions of transmissive region  982  may have discretely differing transparency values or that the transparency of transmissive region  982  may gradually vary in a gradated way across various portions thereof, in accordance with the intensity compensation requirement of far-field intensity pattern  672 . 
     Preferably, although not necessarily, mask  980  is an electronically modulated device such as an LCD screen or similar device. Properties of transmissive region  982  thus may be readily electronically modified in accordance with the output characteristics of reference beam  670 . 
     It is appreciated that the particular shape of transmissive region  982  illustrated in  FIGS.  9  and  10    is exemplary only and that transmissive region  982  may be configured in accordance with any trajectory of output and reference far-field intensity patterns  666  and  672 . Additionally, it is appreciated that transmissive region  982  may include more than one transmissive region. In such a case, a single detector  650  may be used to receive light from all transmissive regions, or a corresponding number of detectors may be positioned with respect to each transmissive region. 
     Furthermore, it is appreciated that transmissive region  982  may additionally or alternatively be configured in accordance with a shape of output and reference far-field intensity patterns  666  and  672 , rather than a trajectory thereof, as is detailed with reference to  FIGS.  11  and  12   . 
     Reference is now made to  FIG.  11   , which is simplified schematic illustration of an optical phased array laser system including a detector mask configured in accordance with an exemplary laser beam shape, constructed and operative in accordance with another preferred embodiment of the present invention. 
     As seen in  FIG.  11   , a system  1100  generally resembling system  900  in relevant aspects thereof may include an optical mask  1180  having at least one transmissive region  1182 , replacing optical mask  980  of  FIGS.  9  and  10   . Optical mask  1180  may resemble optical mask  980  in all relevant aspects thereof, with the exception of transmissive region  1182  being configured in accordance with a shape of reference beam  670  rather than a trajectory thereof. Here, by way of example, transmissive region  1182  is shown to be a bow-tie shaped transmissive region, configured in accordance with a bow-tie shaped output and reference far-field intensity pattern  666  and  672 . 
     Transmissive region  1182  may have non-uniform transparency, a highly simplified representation of which is illustrated in  FIG.  12   . As seen in  FIG.  12   , a first portion of transmissive region  1182  may have a first transparency T 1  and a second portion of transmissive region  1182  may have a second transparency T 2 , different from first transparency T 1 . As detailed hereinabove with reference to  FIG.  10   , various levels of transparency of transmissive region  1182  may be employed in order to compensate for inherent intensity variation in output beam  670  and thus improve the noise correction output provided based on the intensity detected at detector  650 . 
     It is appreciated that transmissive regions  982  and  1182  of masks  980  and  1180  respectively may additionally or alternatively be embodied as reflective regions, reflecting therefrom output reference beam  670  towards detector  650 . In such an arrangement, appropriate modifications and/or additions to focusing subsystem, here embodied by way of example as focusing lens  990 , would be required, in order to direct output reference beam  670  from reflective region  982 ,  1182  onto a surface of detector  650 . The reflective regions of masks  980  and  1180  may have uniform reflectivity. Alternatively, reflective regions of masks  980  and  1180  may have non-uniform reflectivity, in order to compensate for inherent intensity variations in output reference beam  670 , as described hereinabove. 
     In the case that masks  980  and  1180  include a reflective region, masks  980  and  1180  may be embodied as an electrically modulated device such as a digital micromirror device (DMD) or other similar device. 
     It is appreciated that an OPA laser system of the type shown in any of  FIGS.  9 - 12   , including at least one detector receiving an output reference beam via a transmissive or reflective optical mask, may be incorporated in an OPA laser system of the type shown in any of  FIGS.  1 A,  2 A,  3 A and  4 A  in order to provide more efficient noise correction to the phase-varied output thereof. 
     Reference is now made to  FIG.  13   , which is a simplified schematic illustration of an optical phased array laser system including voltage-phase correlating functionality, constructed and operative in accordance with a preferred embodiment of the present invention. 
     As seen in  FIG.  13   , there is provided an OPA laser system  1300 . OPA laser  1300  may be of a type generally resembling OPA lasers  100 ,  200 ,  300 ,  400  described hereinabove with reference to  FIGS.  1 A- 4 C . OPA laser  1300  preferably comprises a seed laser  1312  and a laser beam splitting and combining subsystem  1314 . Splitting and combining subsystem  1314  preferably receives an output laser beam from seed laser  1312  and splits the output laser beam into a plurality of sub-beams along a corresponding plurality of channels  1316 . 
     The relative phase of each sub-beam may be individually modulated by a phase modulator  1318 , preferably located along each of channels  1316 . Each phase modulated sub-beam produced by the splitting and subsequent phase modulation of the output of seed laser  1312  preferably propagates towards a collimating lens  1319 . The individually collimated, phase modulated sub-beams are subsequently combined, for example at a focal plane of a lens  1320 , to form an output beam  1322 . 
     Splitting and combining subsystem  1314  may also provide laser amplification of the sub-beams, preferably following the splitting of the output beam of seed laser  1312  into sub-beams and prior to the combining of the sub-beams to form output beam  1322 . Here, by way of example, splitting and combining subsystem  1314  is shown to include a plurality of optical amplifiers  1324  located along corresponding ones of channels  1316  for amplifying each sub-beam. It is appreciated, however, that such amplification is optional and may be omitted, depending on the power output specifications of OPA laser  1300 . 
     The phase of output beam  1322 , and hence the position and shape of the far-field intensity pattern thereof, is controlled, at least in part, by the relative phases of the constituent sub-beams combined to form output beam  1322 . In many applications, such as laser cutting, laser welding, free-space optical communications and laser additive manufacturing described hereinabove, it is desirable to dynamically move and shape the far-field intensity pattern of the output beam. As described hereinabove with reference to  FIGS.  1 A- 4 C , dynamic variation of parameters of the output beam may be achieved by dynamically varying the relative phases of the individual sub-beams along channels  1316  and thereby varying the phase of the combined laser output  1322  so as to dynamically control the position and shape of the far-field intensity pattern thereof. 
     The relative phases of the sub-beams are preferably predetermined in accordance with the desired laser output pattern. Particularly preferably, the varying relative phases are applied by a phase modulation control module  1330 . Phase modulation control module  1330  preferably provides a voltage to phase modulators  1318  in order for phase modulators  1318  to produce the desired phase modulation of sub-beams along channels  1316 . It is appreciated that phase modulation control module  1330  in combination with phase modulators  1318  forms a particularly preferred embodiment of a phase modulation subsystem  1332 , which phase modulation subsystem  1332  is preferably operative to vary a phase of combined laser output  1322 . 
     In order to facilitate application of phase variation to output beam  1322 , a portion of the output of OPA laser  1300  is preferably extracted and directed towards at least one detector  1350 . The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required phase variation may be calculated. In the embodiment shown in  FIG.  13   , plurality of sub-beams along channels  1316  are directed towards a beam splitter  1360 . Beam splitter  1360  preferably splits each sub-beam into a transmitted portion  1362  and a reflected portion  1364  in accordance with a predetermined ratio. For example, beam splitter  1360  may split each sub-beam with a 99.9% transmitted: 0.01% reflected ratio. 
     The transmitted portion  1362  of the sub-beams preferably propagates towards focal lens  1320 , at which focal lens  1320  the sub-beams are combined to form output beam  1322  having a far-field intensity pattern  1366 . The reflected portion  1364  of the sub-beams preferably propagates towards an additional focal lens  1368 , at which additional focal lens  1368  the sub-beams are combined to form an additional reference beam  1370  having a far-field intensity pattern  1372  incident on a surface of detector  1350 . 
     Detector  1350  preferably samples the far-field intensity pattern  1372  incident thereon. It is appreciated that although detector  1350  is illustrated in  FIG.  13    as being embodied as a single detector directly receiving far-field intensity pattern  1372  thereupon, multiple detectors may alternatively be employed in accordance with any of the multiple detector arrangements illustrated in any of  FIGS.  6 - 8   . Alternatively, a single detector such as detector  1350  may be employed in conjunction with an optical mask, in accordance with any of the arrangements illustrated in any of  FIGS.  9 - 12   . 
     Detector  1350 , in cooperation with phase modulation subsystem  1332 , then preferably optimizes the relative phases of the sub-beams in order to achieve a desired far-field intensity pattern  1372  and corresponding far-field intensity pattern  1366 . Various algorithms suitable for phase optimization include sequential or non-sequential optimization algorithms, including the phase optimization regime described hereinabove with reference to  FIGS.  1 A- 4 C . 
     In operation of phase modulation subsystem  1332 , phase modulation control module  1330  preferably applies a voltage to each of phase modulators  1318  and phase modulators  1318  consequently produce a phase modulating output corresponding to the voltage applied. It is appreciated that in order for phase modulators  1318  to produce the required phase shift so as to dynamically shape far-field intensity pattern  1366  in accordance with a predetermined pattern, phase modulation control module  1330  must apply to each phase modulator  1318  exactly that voltage corresponding to the specific phase modulation output required to be produced by each phase modulator  1318 . 
     In order to ensure that the voltage applied by phase modulation control module  1330  to phase modulators  1318  produces the required and intended phase modulating output by phase modulators  1318 , OPA laser  1300  preferably includes a voltage-to-phase correlation subsystem  1380 . Voltage-to-phase correlation subsystem  1380  is preferably operative to correlate a voltage applied to phase modulation subsystem  1332  to a phase modulating output produced by phase modulation subsystem  1332  and more specifically by phase modulators  1318  thereof. 
     Furthermore, voltage-to-phase correlation subsystem  1380  is preferably operative to provide a voltage-to-phase correlation output useful in calibrating phase modulation subsystem  1332 . Preferably, voltage-to-phase correlation subsystem performs the correlating between the voltage and phase modulating output periodically during the course of varying of the phase of combined laser output  1322 . 
     It is appreciated that the inclusion of a correlation and calibration subsystem such as voltage-to-phase correlation subsystem  1380  in OPA laser  1300  is highly advantageous since it ensures that the voltages being applied to phase modulators  1318  are indeed those voltages required to produce the desired phase shift of output beam  1322  and hence shape of far-field intensity pattern  1366 . This is particularly important given that phase modulators suitable for use in preferred embodiments of the present invention are typically highly sensitive devices, different ones of which typically exhibit different voltage-phase relationships. Furthermore, the voltage-phase relationship of an individual phase modulator is not constant but rather may vary over time and in response to operating conditions. 
     It is appreciated that the phase modulation and calibration provided by phase modulation control module  1330  and voltage-phase correlation control module  1380  respectively, are preferably, although not necessarily, performed in coordination with the application of noise correction to the output of OPA laser  1300  in the case that the output of laser  1300  has noise. In this case, phase modulation control module  1330  and voltage-phase correlation control module  1380  may be considered to combinedly form a particularly preferred embodiment of a phase control subsystem such as phase control subsystem  130  ( FIG.  1 A ),  230  ( FIG.  2 A ),  330  ( FIG.  3 A ) and  430  ( FIG.  4 A ). 
     An exemplary voltage-phase correlation and calibration regime suitable for use in the present invention is illustrated in a flow chart  1400  in  FIG.  14   . It is appreciated, however, that the specific steps of flow chart  1400  are exemplary only and that voltage-phase correlation subsystem  1380  may be implemented as any suitable subsystem within OPA laser  1300  capable of calibrating phase modulation subsystem  1332  periodically during the phase variation of output beam  1322 . Furthermore, it is appreciated that the various steps illustrated in flow chart  1400  are not necessarily performed in the order shown and described and that various ones of the steps may be omitted, or may be supplemented by additional or alternative steps, as will be apparent to one skilled in the art. 
     As seen at a first step  1402 , phase modulation control module  1330  preferably applies a voltage to phase modulators  1318  in order to produce the desired phase shift of sub-beams along channels  1316 . The far-field intensity pattern of the reference output beam  1372  is then measured at detector  1350 , as seen at a second step  1404 . The required phase shift of the sub-beams is then ascertained and a voltage again applied to phase modulators  1318 . The application of a voltage at first step  1402  and measurement of the reference output beam  1372  at second step  1404  may be periodically repeated a large number of times at a given repetition rate. By way of example only, first and second steps may be repeated 20 times at a rate of 1 million times per second. 
     Following the repetition of first and second steps  1402 ,  1404  a predetermined number of times, such as 20 times, voltage-to-phase correlation subsystem  1380  may be activated. As seen a third step  1406 , a voltage intended to produce a phase shift of 2π is preferably applied to one phase modulator  1318 . As seen at a fourth step  1408 , the intensity of far-field intensity pattern  1372  is then measured, preferably at detector  1350 . 
     The phase shift of far-field intensity pattern  1372  is then checked at a fifth step  1410  to ascertain whether the phase shift is zero. It is understood that in the case that the voltage applied at third step  1406  is indeed that voltage producing a phase shift of 2π, the phase shift of beam  1322  would be zero and the intensity of far-field intensity pattern  1372  would thus not change in response to the voltage applied. In this case, the phase modulator  1318  to which the a phase shift was applied at third step  1406  is found to be correctly calibrated and no additional calibration of the particular phase modulator  1318  is required. 
     It is further understood that in the case that the voltage applied at third step  1406  does not produce a phase shift of 2π, the phase shift of beam  1322  would be non-zero and the intensity of far-field intensity pattern  1372  would thus change in response to the voltage applied, as found to be the case at a seventh step  1414 . In this case, the relationship between the applied voltage and the resultant phase shift is preferably derived at seventh step  1414 . Phase modulator  1318  is preferably then calibrated in accordance with the voltage-phase relationship derived at seventh step  1414 , as seen at an eighth step  1416 . 
     As seen at a query  1418 , following the calibration of a particular phase modulator  1318  at eighth calibration step  1416  or ascertainment of proper calibration of a particular phase modulator  1318  at fifth step  1410 , voltage-to-phase correlation subsystem  1380  preferably checks whether a predetermined number of phase modulators  1318  has been calibrated and proceeds to calibrate the next phase modulator if necessary, as seen at a ninth step  1420 . Voltage-to-phase correlation subsystem  1380  may successively calibrate all of phase modulators  1318  included in system  1300  or may successively calibrate a predetermined number of phase modulators  1318 , such as N phase modulators  1318 . Once the predetermined number of phase modulators  1318  has been calibrated, subsystem  1380  is preferably deactivated and phase variation of output beam  1322  is resumed at step  1402 . 
     It is understood that the frequency at which voltage-to-phase correlation subsystem  1380  is activated is preferably significantly lower than the frequency at which phase variation of output beam  1322  is performed. By way of example phase variation of output beam  1322  may be performed 1 million times per second while voltage-to-phase correlation may be activated 1 time per second. 
     Furthermore, it is understood that although flow chart  1400  does not include steps for noise correction, such noise correction may be applied during the course of the phase shifting of the sub-beams contributing to output beam  1322 , as described hereinabove with reference to  FIGS.  1 A- 4 C . 
     Reference is now made to  FIG.  15   , which is a simplified schematic plan view illustration of an optical phased array laser system including scaled phase modification of dynamic beams, constructed and operative in accordance with an additional preferred embodiment of the present invention. 
     As seen in  FIG.  15   , there is provided an optical phased array (OPA) laser system  1500 , which OPA laser  1500  may be of a type generally described hereinabove with reference to  FIGS.  1 A- 4 C . OPA laser  1500  preferably comprises a seed laser  1512  and a laser beam splitting and combining subsystem  1514 . Splitting and combining subsystem  1514  preferably receives an output laser beam from seed laser  1512  and splits the output laser beam into a plurality of sub-beams along a corresponding plurality of channels  1516 . Here, by way of example only, an output from seed laser  1512  may be split into a 4×4 matrix of 16 sub-beams along 16 corresponding channels  1516 , four of which sub-beams and channels  1516  are seen in the top view of OPA laser  1500  in  FIG.  15   . It is appreciated, however, that splitting and combining subsystem  1514  may include a fewer or greater number of channels along which the output of seed laser  1512  is split, and typically may include a far greater number of channels such as 32 or more channels. 
     The relative phase of each sub-beam may be individually modulated by a phase modulator  1518 , preferably located along each of channels  1516 . Each phase modulated sub-beam produced by the splitting and subsequent phase modulation of the output of seed laser  1512  preferably propagates towards a collimating lens  1519 . The individually collimated, phase modulated sub-beams are subsequently combined, for example at a focal plane of lens  1520 , to form an output beam  1522 . 
     Splitting and combining subsystem  1514  may also provide laser amplification of the sub-beams, preferably following the splitting of the output beam of seed laser  1512  into sub-beams and prior to the combining of the sub-beams to form output beam  1522 . Here, by way of example, splitting and combining subsystem  1514  is shown to include a plurality of optical amplifiers  1524  located along corresponding ones of channels  1516  for amplifying each sub-beam. It is appreciated, however, that such amplification is optional and may be omitted, depending on the power output specifications of OPA laser  1500 . 
     The phase of output beam  1522 , and hence the position and shape of the far-field intensity pattern thereof, is controlled, at least in part, by the relative phases of the constituent sub-beams combined to form output beam  1522 . In many applications, such as laser cutting, laser welding, free-space optical communications and laser additive manufacturing, as described hereinabove, it is desirable to dynamically move and shape the far-field intensity pattern of the output beam. As described hereinabove with reference to  FIGS.  1 A- 4 C , dynamic variation of parameters of the output beam may be achieved by dynamically varying the relative phases of the individual sub-beams along channels  1516  and thereby varying the phase of the combined laser output  1522  so as to dynamically control the position and shape of the far-field intensity pattern thereof. 
     In the case of OPA laser  1500  including a large number of individual sub-beams, phase measurement and corresponding phase modification of each sub-beam with respect to the phases of all of the other ones of the sub-beams, may be challenging due to the large number of individual sub-beams involved. Specifically, due to the large number of individual sub-beams contributing to the combined output  1522 , the time taken to measure and modify the phase of each individual sub-beam with respect to the other sub-beams so as to dynamically control the phase of the combined laser output  1522  may be unacceptably long. Furthermore, the signal to noise ratio may be unacceptably low. 
     It is a particular feature of a preferred embodiment of the present invention that OPA laser  1500  preferably includes a phase modulation subsystem  1530  for carrying out phase modulation of the combined laser output in a scaled manner. More specifically, phase modulation subsystem  1530  preferably groups at least a portion of the sub-beams provided by laser splitting and combining subsystem  1514  into groups and then performs phase modulation within each group of sub-beams, only with respect to other sub-beams within the group. Such group phase modulation is preferably performed in parallel across various individual groups of sub-beams. Phase modulation subsystem  1530  then preferably optimizes the phase of each group of sub-beams with respect to the phases of other ones of the groups of sub-beams, in order to vary the phase of the combined laser output  1522 , in a manner detailed henceforth. 
     Phase modulation subsystem  1530  preferably includes a phase control electronic module  1532  in operative control of phase modulators  1518 . Phase control electronic module  1532  preferably controls each phase modulator  1518  so as to dynamically modulate the relative phases of the sub-beams along channels  1516 , in accordance with the desired far-field intensity pattern of output beam  1522 , as ascertained by phase modulation subsystem  1530 . 
     In order to facilitate application of phase variation to output beam  1522 , a portion of the output of OPA laser  1500  is preferably extracted and directed towards a plurality of detectors  1550 . The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required phase variation may be calculated. In the embodiment shown in  FIG.  15   , plurality of sub-beams along channels  1516  are directed towards a beam splitter  1560 . Beam splitter  1560  preferably splits each sub-beam into a transmitted portion  1562  and a reflected portion  1564  in accordance with a predetermined ratio. For example, beam splitter  1560  may split each sub-beam with a 99.9% transmitted: 0.01% reflected ratio. 
     The transmitted portion  1562  of the sub-beams preferably propagates towards focal lens  1520 , at which focal lens  1520  the sub-beams are combined to form output beam  1522  having a far-field intensity pattern  1566 . The reflected portion  1564  of the sub-beams preferably propagates towards a cylindrical lens  1568 . Cylindrical lens  1568  is preferably operative to receive the reflected portion  1564  of the sub-beams and group the sub-beams into a multiplicity of groups, by converging the sub-beams along a direction of curvature of lens  1568 . Here, by way of example, the sub-beams are shown to be converged into four groups  1570 , each group  1570  being made up of four sub-beams. 
     Preferably, each group  1570  of sub-beams grouped by cylindrical lens  1568  forms a beam having a far-field intensity pattern  1572  incident on a surface of corresponding one of plurality of detectors  1550 . Each detector  1550  preferably samples the group far-field intensity pattern  1572  incident thereon. Each detector  1550 , in cooperation with a corresponding control electronics sub-module  1574  included in control module  1532 , then preferably optimizes the relative phases of the sub-beams within the group of sub-beams  1570  sampled thereby, with respect to the phases of the other sub-beams within the group  1570 . Such sampling and optimization is preferably carried out in parallel and preferably simultaneously for ones of far-field intensity patterns  1572  across all of detectors  1550 . Various algorithms suitable for phase optimization include sequential or non-sequential optimization algorithms including noise correction algorithms, such as described above with reference to  FIGS.  1 A- 4 C . 
     In order to optimize the relative phase of each of groups  1570  with respect to other ones of groups  1570 , a portion of groups  1570  is preferably directed, by way of an auxiliary beam splitter  1580 , to an auxiliary cylindrical lens  1582 . It is appreciated that the curvature of auxiliary cylindrical lens  1582  is preferably orthogonal with respect to the curvature of cylindrical lens  1568  in order to focus the sub-beams. Auxiliary cylindrical lens  1582  preferably causes groups of sub-beams  1570  to converge into a single beam  1584  having a far-field intensity pattern  1586  incident on an auxiliary detector  1588 . Auxiliary detector  1588  preferably receives thereat a single beam having a far field intensity pattern  1586  corresponding to that of a combination of all of groups of sub-beams  1570 . Auxiliary detector  1588  preferably samples and optimizes the phases of groups  1570  with respect to each other, in cooperation with an additional phase control electronics sub-module  1590  included in electronic control module  1532 . Particularly preferably, one function of phase control electronic module  1532  is to control each phase modulator  1518  so as to apply a phase shift maximizing the total power on auxiliary detector  1588 . 
     It is appreciated that carrying out phase modulation in the above-described scaled manner, wherein the phase of each sub-beam is optimized with respect to the phases of other sub-beam members of its group  1570  and the phases of groups  1570  are optimized with respect to each other so as to vary the phase of the combined laser output  1522 , is far quicker and less complex than optimizing the phase of each individual sub-beam with respect to the phases of all of the other sub-beams in OPA  1500 . Furthermore, this allows the phase optimization to be carried out by individual sets of control electronics in each control electronics sub-module  1574  respectively coupled to each detector  1550 , rather than requiring a single set of control electronics and improves the signal to noise ratio. 
     It is appreciated that the functionality of optimizing the relative phase of each of groups  1570  with respect to other ones of groups  1570  may alternatively be carried out by additional group phase modulators, operative to modulate the collective phase of each of groups  1570 , rather than by individual phase modulators  1518  operative to modulate the individual phase of each sub-beam member of each of groups  1570 . An exemplary implementation of such an arrangement is illustrated in  FIG.  16    and may generally resemble the phase modulation arrangement described in U.S. Pat. No. 9,893,494, the disclosure of which is hereby incorporated by reference, in some aspects thereof. 
     As seen in  FIG.  16   , system  1500  may be modified by adding a series of group phase modulators corresponding to the number of groups  1570 . Here, by way of example, system  1500  comprises 16 sub-beams, four of which sub-beams are included in each of four groups  1570 , such that a total of four additional group phase modulators  1618  may be included in system  1500 , as seen in  FIG.  16   . Each group phase modulator  1618  is preferably common to the four channels  1516  forming part of each group  1570  and provides a phase shift optimizing the collective group phase of the sub-beams along the four channels  1516  connected thereto. 
     Preferably, ones of group phase modulator  1618  are controlled by an additional control sub-module  1690 , preferably included in control module  1532 . Auxiliary detector  1588  is preferably coupled to the additional control sub-module  1690 . It is appreciated that optimizing the relative phases of groups  1570  with respect to each other by group phase modulators  1618  rather than by individual sub-beam phase modulators  1518  may be more efficient and may simplify the phase modulation process, but requires the employment of additional phase modulating and circuitry elements, thus increasing the cost and complexity of system  1500 . 
     Variation of the phase of combined laser output  1522  preferably provides spatial modulation of the output  1522 . It is appreciated that, due to the scaled nature of the phase modulation carried out by phase modulation subsystem  1530 , the phase of combined laser output  1522  may be varied very rapidly, at a rate greater than that achievable by mechanical spatial modulation mechanisms. The spatial modulation provided by OPA laser  1500  may optionally be augmented by additional mechanical spatial modulation mechanisms, as are known in the art, or may not involve mechanical spatial modulation. 
     It is understood that the particular structure and configuration of optical elements shown herein, including beam splitter  1560 , focal lens  1520 , cylindrical lens  1568 , auxiliary beam splitter  1580  and auxiliary cylindrical lens  1582  is exemplary only and depicted in a highly simplified form. It is appreciated that OPA laser system  1500  may include a variety of such elements, as well as additional optical elements, including, by way of example only, additional or alternative lenses, optical fibers and coherent free-space far-field combiners. 
     Furthermore, it is appreciated that cylindrical lens  1568  may have optical properties so as to group the individual sub-beams into mutually similar or identical groups comprising equal numbers of sub-beams. Alternatively, cylindrical lens  1568  may have optical properties so as to group the individual sub-beams into mutually differing groups comprising different numbers of sub-beams. 
     An exemplary implementation of an OPA laser system of the type illustrated in  FIG.  15    or  FIG.  16    is shown in  FIGS.  17 A and  17 B . Turning now to  FIGS.  17 A and  17 B , an OPA laser system  1700  is provided wherein an output laser beam from a seed laser (not shown) such as seed laser  1512  is split into a plurality of sub-beams along a corresponding plurality of channels  1716 . By way of example, the laser output may be split, by way of example, into a 10×10 matrix of 100 sub-beams along 100 corresponding channels  1716 . It is appreciated that, for the sake of clarity of presentation, only selected ones of the sub-beams are illustrated in  FIG.  17 B . Sub-beams along channels  1716  may subsequently be collimated and focused by collimating and focusing elements (not shown) such as collimating and focusing lenses  1519 ,  1520 , to produce a combined output beam. 
     In order to facilitate application of phase variation to the output beam, a portion of the output of OPA laser  1700  is preferably extracted and directed towards a plurality of detectors  1750 . The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required phase variation may be calculated. In the embodiment shown in  FIGS.  17 A and  17 B , plurality of sub-beams along channels  1716  are directed towards a beam splitter  1760 . Beam splitter  1760  preferably splits each sub-beam into a transmitted portion  1762  and a reflected portion  1764  in accordance with a predetermined ratio. 
     The transmitted portion  1762  of the sub-beams is preferably combined to form the output beam. The reflected portion  1764  of the sub-beams is preferably reflected towards a cylindrical lens  1768 , which cylindrical lens  1768  is particularly preferred embodiment of cylindrical lens  1568 . Cylindrical lens  1768  is preferably operative to receive the reflected portion  1764  of the sub-beams and cause the sub-beams to converge into a multiplicity of groups along a direction of curvature of cylindrical lens  1768 . By way of example, in the case of 100 sub-beams, cylindrical lens  1768  may cause the sub-beams to converge into ten groups  1770  of ten sub-beams. 
     Preferably, each group  1770  of sub-beams grouped by cylindrical lens  1768  forms a beam having a far field intensity pattern incident on a surface of corresponding one of plurality of detectors  1750 . By way of example plurality of detectors  1750  may include ten detectors  1750 , each sampling a group beam comprising ten individual sub-beams. Each detector  1750 , in cooperation with a corresponding control electronics module (not shown) such as control module  1532 , then preferably optimizes the phases of the sub-beams included in the group  1770  of sub-beams sampled thereby, Such sampling and optimization is preferably carried out in parallel and preferably simultaneously across all of detectors  1750 . 
     In order to optimize the relative phase of each of groups  1770  with respect to the phases of other ones of groups  1770 , a portion of groups  1770  is preferably directed, by way of an auxiliary beam splitter  1780 , to an auxiliary cylindrical lens  1782 . It is appreciated that auxiliary cylindrical lens  1782  is a particularly preferred embodiment of auxiliary cylindrical lens  1582 . It is appreciated that the curvature of auxiliary cylindrical lens  1782  is preferably orthogonal with respect to the curvature of cylindrical lens  1768  in order to focus the sub-beams. Auxiliary cylindrical lens  1782  preferably focuses groups of sub-beams  1770  into one combined beam  1784  incident on an auxiliary detector  1788 . 
     Auxiliary detector  1788  preferably receives thereat a far field intensity pattern corresponding to that of a combination of all of groups of sub-beams  1770  and samples and optimizes the phases of groups  1770  with respect to each other, in cooperation with phase control electronics (not shown). It is appreciated that the optimization of the phases of groups  1770  with respect to each other may be by way of phase modulation of the phases of the individual sub-beams by phase modulators  1518 , as described hereinabove with reference to  FIG.  15   , or may be by way of phase modulation of the phases of the groups of sub-beams by group phase modulators  1618 , as described hereinabove with reference to  FIG.  16   . 
     Reference is now made to  FIG.  18   , which is a simplified schematic plan view illustration of an optical phased array laser system including scaled phase modification of dynamic beams, constructed and operative in accordance with another preferred embodiment of the present invention. 
     As seen in  FIG.  18   , there is provided an optical phased array (OPA) laser system  1800 , which OPA laser  1800  may be of a type generally described hereinabove with reference to  FIGS.  1 A- 4 C . OPA laser  800  preferably comprises a seed laser  1812  and a laser beam splitting and combining subsystem  1814 . Splitting and combining subsystem  1814  preferably receives an output laser beam from seed laser  1812  and splits the output laser beam into a plurality of sub-beams along a corresponding plurality of channels  1816 . Here, by way of example only, an output from seed laser  1812  may be split into a 4×4 matrix of 16 sub-beams along 16 corresponding channels  1816 , four of which sub-beams and channels  1816  are seen in the top view of OPA laser  1800  in  FIG.  18   . It is appreciated, however, that splitting and combining subsystem  1814  may include a fewer or greater number of channels along which the output of seed laser  1812  is split, and typically may include a far greater number of channels such as 32 or more channels. 
     The relative phase of each sub-beam may be individually modulated by a phase modulator  1818 , preferably located along each of channels  1816 . Each phase modulated sub-beam produced by the splitting and subsequent phase modulation of the output of seed laser  402  preferably propagates towards a collimating lens  1819 . The individually collimated, phase modulated sub-beams are subsequently combined, for example at a focal plane of a lens  1820 , to form an output beam  1822 . 
     Splitting and combining subsystem  1814  may also provide laser amplification of the sub-beams, preferably following the splitting of the output beam of seed laser  1812  into sub-beams and prior to the combining of the sub-beams to form output beam  1822 . Here, by way of example, splitting and combining subsystem  1814  is shown to include a plurality of optical amplifiers  1824  located along corresponding ones of channels  1816  for amplifying each sub-beam. It is appreciated, however, that such amplification is optional and may be omitted, depending on the power output requirements of OPA laser  1800 . 
     The phase of output beam  1822 , and hence the position and shape of the far-field intensity pattern thereof, is controlled, at least in part, by the relative phases of the constituent sub-beams combined to form output beam  1822 . In many applications, such as laser cutting, laser welding, free-space optical communications and laser additive manufacturing, as described hereinabove, it is desirable to dynamically move and shape the far-field intensity pattern of the output beam. As described hereinabove with reference to  FIGS.  1 A- 4 C , dynamic variation of parameters of the output beam may be achieved by dynamically varying the relative phases of the individual sub-beams along channels  1816  and thereby varying the phase of the combined laser output  1822  so as to dynamically control the position and shape of the far-field intensity pattern thereof. 
     In the case of OPA laser  1800  including a large number of individual sub-beams, phase measurement and corresponding phase modification of each sub-beam with respect to the phases of all of the other ones of the sub-beams, may be challenging due to the large number of individual sub-beams involved. Specifically, due to the large number of individual sub-beams contributing to the combined output  1822 , the time taken to measure and modify the phase of each individual sub-beam with respect to the other sub-beams so as to dynamically control the phase of the combined laser output  1822  may be unacceptably long. Furthermore, the signal to noise ratio may be unacceptably low. 
     It is a particular feature of a preferred embodiment of the present invention that OPA laser  1800  preferably includes a phase modulation subsystem  1830  for carrying out phase modulation of the combined laser output in a scaled manner. More specifically, phase modulation subsystem  1830  preferably groups at least a portion of the sub-beams provided by laser splitting and combining subsystem into groups and then performs phase modulation within each group of sub-beams, only with respect to the phases of other sub-beams within the group. Such group phase modulation is preferably performed in parallel across various individual groups. Phase modulation subsystem  1830  then preferably optimizes the phase of each group of sub-beams with respect to the phases of other ones of the groups of sub-beams, in order to vary the phase of the combined laser output  1822 , in a manner detailed henceforth. 
     Phase modulation subsystem  1830  preferably includes a phase control electronic module  1832  in operative control of phase modulators  1818 . Phase control electronic module  1832  preferably controls each phase modulator  1818  so as to dynamically modulate the relative phases of the sub-beams along channels  1816 , in accordance with the desired far-field intensity pattern of output beam  1822  and as ascertained by phase modulation subsystem  1830 . 
     In order to facilitate application of phase variation to output beam  1822 , a portion of the output of OPA laser  1800  is preferably extracted and directed towards a plurality of detectors  1850 . The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required phase variation may be calculated. In the embodiment shown in  FIG.  18   , plurality of sub-beams along channels  1816  are directed towards a beam splitter  1860 . Beam splitter  1860  preferably splits each sub-beam into a transmitted portion  1862  and a reflected portion  1864  in accordance with a predetermined ratio. For example, beam splitter  1860  may split each sub-beam with a 99.9% transmitted: 0.01% reflected ratio. 
     The transmitted portion  1862  of the sub-beams preferably propagates towards focal lens  1820 , at which focal lens  1820  the sub-beams are combined to form output beam  1822  having a far-field intensity pattern  1866 . The reflected portion  1864  of the sub-beams is preferably reflected towards an array of mirrors  1868 , each mirror  1868  being positioned in spaced relation to a corresponding focusing lens  1869 . By way of example, array of mirrors  1868  may comprise four mirrors  1868  positioned in spaced relation to four focusing lenses  1869 , two of which mirrors and focusing lenses are visible in the top view of system  1800  in  FIG.  18   . 
     Mirrors  1868  are preferably angled so as to be operative to reflect sub-beams incident thereon towards the corresponding focusing lens  1869  and thereby group the reflected portion  1864  of the sub-beams into a multiplicity of groups, here embodied, by way of example, as four groups  1870 , each group  1870  including four sub-beams, two of which groups are seen in the top view of system  18100  in  FIG.  18   . 
     Preferably, each group of sub-beams reflected at each of mirrors  1868  is focused by the corresponding focal lens  1869  to form a single beam comprising group of sub-beams  1870  and having a far-field intensity pattern  1872  incident on a surface of a corresponding one of plurality of detectors  1850 . Each detector  1850 , in cooperation with a corresponding control electronics sub-module  1874  included in control module  1832 , then preferably optimizes the relative phases of the sub-beams within the group of sub-beams  1870  sampled thereby, with respect to the phases of the other sub-beams within the group  1870 . Such sampling and optimization is preferably carried out in parallel and preferably simultaneously for ones of far-field intensity patterns  1872  across all of detectors  1850 . Various algorithms suitable for phase optimization include sequential or non-sequential optimization algorithms including noise correction algorithms, as described hereinabove with reference to  FIGS.  1 A- 4 C . 
     In order to optimize the relative phase of each of groups  1870  with respect to other ones of groups  1870 , a portion of reflected portion  1864  is preferably directed, by way of an auxiliary beam splitter  1880 , to an auxiliary lens  1882 . Auxiliary lens  1882  preferably causes the sub-beams incident thereon to converge into a single beam  1884  having a far-field intensity pattern  1886  incident on an auxiliary detector  1888 . Auxiliary detector  1888  preferably receives thereat a single beam having a far field intensity pattern  1886  corresponding to that of a combination of all of groups of sub-beams  1870 . Auxiliary detector  1888  preferably samples and optimizes the phases of groups  1870  with respect to each other, in cooperation with a phase control electronics sub-module  1890  included in electronic control module  1832 . Particularly preferably, one function of phase control electronic module  1832  is to control each phase modulator  1818  so as to apply a phase shift maximizing the total power on auxiliary detector  1888 . 
     It is appreciated that carrying out phase modulation in the above-described scaled manner, wherein the phase of each sub-beam is optimized with respect to the phases of other sub-beam members of its group  1870  and the phases of groups  1870  are optimized with respect to each other to vary the phase of the combined laser output  1822 , is far quicker and less complex than optimizing the phase of each individual sub-beam with respect to the phases of all of the other sub-beams in OP  1800 . Furthermore, this allows the phase optimization to be carried out by individual sets of control electronics in each control electronics sub-module  1874  coupled to each detector  1850 , rather than requiring a single set of control electronics and improves the signal to noise ratio. 
     It is appreciated that the functionality of optimizing the relative phase of each of groups  1870  with respect to other ones of groups  1870  may alternatively be carried out by additional group phase modulators, operative to modulate the collective phase of each of groups  1870 , rather than by individual phase modulators  1818  operative to modulate the individual phase of each sub-beam member of each of groups  1870 . An exemplary implementation of such an arrangement is illustrated in  FIG.  19    and may generally resemble the phase modulation arrangement described in U.S. Pat. No. 9,893,494 in some aspects thereof. 
     As seen in  FIG.  19   , system  1800  may be modified by adding a series of group phase modulators corresponding to the number of groups  1870 . Here, by way of example, system  1800  comprises 16 sub-beams, four of which sub-beams are included in each of four groups  1870 , such that a total of four additional group phase modulators  1918  may be included in system  1800 , as seen in  FIG.  19   . Each group phase modulator  1918  is preferably common to the four channels  1816  forming part of each group  1870  and provides a phase shift optimizing the collective group phase of the sub-beams along the four channels  1816 . 
     Preferably, ones of group phase modulator  1918  are controlled by an additional control sub-module  1990 , preferably included in control module  1832 . Auxiliary detector  1888  is preferably coupled to the additional control sub-module  1990 . It is appreciated that optimizing the relative phases of groups  1870  with respect to each other by group phase modulators  1918  rather than by individual sub-beam phase modulators  1818  may be more efficient and may simplify the phase modulation process, but requires the employment of additional phase modulating and circuitry elements, thus increasing the cost and complexity of system  1800 . 
     Variation of the phase of combined laser output  1822  preferably provides spatial modulation of the output  1822 . It is appreciated that, due to the scaled nature of the phase modulation carried out by phase modulation subsystem  1830 , the phase of combined laser output  1822  may be varied very rapidly, at a rate greater than that achievable by mechanical spatial modulation mechanisms. The spatial modulation provided by OPA laser  1800  may optionally be augmented by additional mechanical spatial modulation mechanisms, as are known in the art, or may not involve mechanical spatial modulation. 
     It is understood that the particular structure and configuration of optical elements shown herein, including beam splitter  1860 , focal lens  1820 , array of mirrors  1868  and corresponding focal lenses  1869  is exemplary only and depicted in a highly simplified form. It is appreciated that OPA laser system  1800  may include a variety of such elements, as well as additional optical elements, including, by way of example only, additional or alternative lenses, optical fibers and coherent free-space far-field combiners. 
     Furthermore, it is appreciated that mirrors  1868  and corresponding focal lenses  1869  may have mutually similar or identical optical properties, so as to group the individual sub-beams into mutually similar or identical groups comprising equal numbers of sub-beams. Alternatively, mirrors  1868  and corresponding focal lenses  1869  may have mutually different optical properties so as to group the individual sub-beams into mutually differing groups comprising different numbers of sub-beams. 
     An exemplary implementation of an OPA laser system of the type illustrated in  FIG.  18    or  FIG.  19    is shown in  FIGS.  20 A and  20 B . Turning now to  FIGS.  20 A and  20 B , an OPA laser system  2000  is provided wherein an output laser beam from a seed laser (not shown) such as seed laser  1812  is split into a plurality of sub-beams along a corresponding plurality of channels  2016 . Here, by way of example only, the laser output may be split into a 10×10 matrix of 100 sub-beams along 100 corresponding channels  2016 , only selected ones of which sub-beams are illustrated in  FIG.  20 B  for the sake of clarity of presentation. Sub-beams along channels  2016  may subsequently be collimated and focused by collimating and focusing elements (not shown) such as collimating and focusing lenses  1819 ,  1820 , to produce a combined output beam. 
     In order to facilitate application of phase variation to the output beam, a portion of the output of OPA laser  2000  is preferably extracted and directed towards a plurality of detectors  2050 . The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required phase variation may be calculated. In the embodiment shown in  FIGS.  20 A and  20 B , plurality of sub-beams along channels  2016  are directed towards a beam splitter  2060 . Beam splitter  2060  preferably splits each sub-beam into a transmitted portion  2062  and a reflected portion  2064  in accordance with a predetermined ratio. 
     The transmitted portion  2062  of the sub-beams is preferably combined to form the output beam. The reflected portion  2064  of the sub-beams is preferably reflected towards an array of mirrors  2068 , each mirror  2068  being positioned in spaced relation to a corresponding focusing lens  2069 . It is appreciated that array of mirrors  2068  and lenses  2069  are particularly preferred embodiments of array of mirrors  1868  and focusing lenses  1869 . 
     Mirrors  2068  are preferably angled so as to be operative to reflect sub-beams incident thereon towards the corresponding focusing lens  2069  and thereby group the reflected portion  2064  of sub-beams into a multiplicity of groups, here embodied, by way of example, as four groups, each group  2070  including 25 sub-beams. Preferably, each set of sub-beams reflected at each of mirrors  2068  is focused by the corresponding focal lens  2069  to form a single beam including group of 25 sub-beams  2070 . Each group of sub-beams  2070  is incident on a surface of corresponding one of plurality of detectors  2050 . Each detector  2050  preferably samples the far-field intensity pattern incident thereon. Each detector  2050 , in cooperation with a corresponding control electronics sub-module (not shown) such as control electronics sub-module  1874  included in control module  1832 , then preferably optimizes the phases of the sub-beams included in the group of sub-beams  2070  sampled thereby, in order for the combined phases to produce a desired group far-field intensity pattern. Such sampling and optimization is preferably carried out in parallel and preferably simultaneously for ones of far-field intensity patterns across all of detectors  2050 . 
     In order to optimize the relative phase of each of groups  2070  with respect to other ones of groups  2070 , a portion of the reflected portion  2064  is preferably directed, by way of an auxiliary beam splitter  2080 , to an auxiliary lens  2082 . Auxiliary lens  2082  preferably causes a portion of the reflected portion  2064  to converge into a single beam  2084  incident on an auxiliary detector  2088 . Auxiliary detector  2088  preferably receives thereat a single beam having a far field intensity pattern corresponding to that of a combination of all of the sub-beams. Auxiliary detector  2088  preferably samples and optimizes the phases of groups  2070  with respect to each other, in cooperation with phase control electronics included in electronic control module  1832 . 
     It is appreciated that the optimization of the phases of groups  2070  with respect to each other may be by way of phase modulation of the phases of the individual sub-beams by phase modulators  1818 , as described hereinabove with reference to  FIG.  18   , or may be by way of phase modulation of the phases of the groups of sub-beams by group phase modulators  1918 , as described hereinabove with reference to  FIG.  19   . 
     It is understood that in the above-described embodiments of OPA lasers  1500 ,  1700 ,  1800  and  2000  of  FIGS.  15 - 20 B , phase modulation is preferably carried out in a scaled manner, with multiple detectors such as detectors  1550 ,  1750 ,  1850  and  2050  employed for simultaneously performing phase measurements of sub-beams within multiple groups and a single detector, such auxiliary detector  1586 ,  1786 ,  1886  and  2086 , employed for performing phase measurements of a single beam including the multiple groups. 
     It is appreciated, however, that a system constructed and operative in accordance with preferred embodiments of the present invention may be further scalable, to include still additional hierarchies of detectors and corresponding optical elements, depending on the number of sub-beams involved. 
     By way of example, as shown in  FIG.  21   , OPA laser system  1500  may be modified to include additional focusing lenses  2102  for focusing groups  1570  of sub-beams into intermediate groups  2104  which intermediate groups are incident on intermediate detectors  2106 . Intermediate groups  2104  are then further combined and incident on a single detector  2108 , at which single detector  2108  intermediate groups  2104  are preferably phase modified with respect to each other. 
     It is additionally understood that any of the OPA laser systems described hereinabove with reference to  FIGS.  15 - 21    may be modified by replacing one or more of the individual detectors therein with multiple detectors and corresponding multiple closely spaced optical pathways, in order to improve the sampling of the output beams, in accordance with embodiments of the present invention described hereinabove with reference to  FIGS.  6 - 8   . Furthermore, any of the OPA laser systems described hereinabove with reference to  FIGS.  15 - 21    may alternatively be modified to include a transmissive or reflective detector mask masking one or more of the multiple detectors employed therein, in accordance with embodiments of the present invention described hereinabove with reference to  FIGS.  9 - 12   , in order to further improve the sampling of the output beams. 
     It is furthermore understood that any of the OPA laser systems described hereinabove with reference to  FIGS.  15 - 21    may be modified to include voltage-phase calibration functionality, in accordance with preferred embodiments of the present invention described hereinabove with reference to  FIGS.  13  and  14   , in order to ensure correct calibration of the phase modulators employed therein. 
     Reference is now made to  FIGS.  22 A and  22 B , which are simplified schematic illustrations of respective first and second focal states of an optical phased array laser system constructed and operative in accordance with a preferred embodiment of the present invention. 
     As seen in  FIGS.  22 A and  22 B , there is provided a laser system  2200  preferably including an optical phased array (OPA) laser  2202 . OPA laser system  2200  may be of the type generally described in U.S. Pat. No. 9,584,224 or in U.S. patent application Ser. No. 15/406,032, assigned to the same assignee as the present invention, the contents of which are incorporated herein by reference. Alternatively, OPA laser system  2200  may be a laser system of the type described in reference to any one, or a combination of ones, of  FIGS.  1 A- 21    hereinabove. 
     As best seen at an enlargement  2210 , OPA laser  2202  preferably includes a seed laser  2212  and a laser beam splitting and combining subsystem  2214  receiving a laser output from seed laser  2212  and providing a combined laser output. Laser beam splitting and combining subsystem  2214  preferably includes a plurality of phase modulators  2218  for varying a phase of the combined laser output, preferably following the splitting of the laser output from seed laser  2212  and prior to the combining performed by splitting and combining subsystem  2214 . 
     Each phase modulated sub-beam produced by the splitting and subsequent phase modulation of the output of seed laser  2212  preferably propagates towards a collimating lens  2219 . The individually collimated, phase modulated sub-beams are subsequently combined, for example at a focal lens  2220 , to form an output beam  2222 . 
     Splitting and combining subsystem  2214  may also provide laser amplification of the sub-beams, preferably following the splitting of the output beam of seed laser  2212  into sub-beams and prior to the combining of the sub-beams to form output beam  2222 . Here, by way of example, splitting and combining subsystem  2214  is shown to include a plurality of optical amplifiers  2224  for amplifying each sub-beam. It is appreciated, however, that such amplification is optional and may be omitted, depending on the power output specifications of OPA laser  2200 . 
     The phase of output beam  2222 , and hence the position and shape of the far-field intensity pattern thereof, is controlled, at least in part, by the relative phases of the constituent sub-beams combined to form output beam  2222 . As described hereinabove with reference to  FIGS.  1 A- 5 G , in many applications, such as laser cutting, laser welding, laser additive manufacturing and optical free space communications, it is desirable to dynamically move and shape the far-field intensity pattern of the output beam  2222 . This may be achieved in laser system  2200  by laser splitting and combining subsystem  2214  dynamically varying the relative phases of the individual sub-beams and thereby varying the phase of the combined laser output  2222  so as dynamically to control the position and shape of the far-field intensity pattern thereof. 
     The relative phases of the sub-beams are preferably predetermined in accordance with the desired laser output pattern. Particularly preferably, the varying relative phases are applied by a phase control subsystem  2230 . Phase control subsystem  2230  preferably forms a part of a control electronics module  2232  in OPA laser system  2200  and preferably controls each phase modulator  2218  so as to dynamically modulate the relative phases of the sub-beams, preferably as described hereinabove with reference to phase control subsystem  130 ,  230 ,  330 ,  430  of  FIGS.  1 A,  2 A,  3 A and  4 A  respectively. 
     Due to noise inherent in OPA system  2200 , output beam  2222  may have noise. Noise in output beam  2222  is typically phase noise created by thermal or mechanical effects and/or by the amplification process in the case that optical amplifiers  2224  are present in OPA system  2200 . In the case that output beam  2222  has noise, OPA system  2200  may include a noise cancellation subsystem  2240  operative to provide a noise cancellation phase correction output in order to cancel out the noise in output beam  2222  in a manner detailed henceforth. 
     Particularly preferably, noise cancellation subsystem  2240  employs an algorithm to sense and correct phase noise in the combined laser output, preferably, although not necessarily, of the type described hereinabove with reference to  FIGS.  1 A- 4 C . The noise cancellation phase correction output is preferably provided by noise cancellation subsystem  2240  to phase modulators  2218  so as to correct phase noise in output beam  2222  and thus avoid distortion of the shape and position of the far field intensity pattern of output beam  2222  that would otherwise be caused by the noise. Noise cancellation subsystem  2240  may be included in control electronics module  2232 . 
     Alternatively, in the case that noise in output beam  2222  is not of significance, noise cancellation subsystem  2240  may be obviated from OPA system  2200  and noise correction correspondingly not performed. 
     In order to facilitate application of phase variation and noise correction if relevant to output beam  2222 , a portion of the output of OPA laser  2202  is preferably extracted and directed towards at least one detector  2250 . Here, by way of example, at least one detector  2250  is shown to be embodied as a single detector  2250 . However, it is understood that at least one detector  2250  may be embodied as multiple detectors receiving a portion of the output of OPA laser  2202  by way of closely spaced optical pathways, as described hereinabove with reference to  FIGS.  6 - 8   , or may be embodied as at least one detector receiving a portion of the output of OPA laser  2202  via a transmissive or reflective optical mask, as described hereinabove with reference to  FIGS.  9 - 12   . The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required noise correction and/or phase variation may be calculated. 
     In accordance with a preferred embodiment of the present invention, plurality of sub-beams along channels  2216  are directed towards a beam splitter  2260 . Beam splitter  2260  preferably splits each sub-beam into a transmitted portion  2262  and a reflected portion  2264  in accordance with a predetermined ratio. For example, beam splitter  2260  may split each sub-beam with a 99.9% transmitted: 0.01% reflected ratio. 
     The transmitted portion  2262  of the sub-beams preferably propagates towards focal lens  2220 , at which focal lens  2220  the sub-beams are combined to form output beam  2222  having a far-field intensity pattern  2266 . The reflected portion  2264  of the sub-beams is preferably reflected towards an additional focal lens  2268 , at which additional focal lens  2268  the sub-beams are combined to form an output reference beam  2270  having a far-field intensity pattern  2272  incident on a surface of one or more of plurality of detectors  2250 . 
     In certain applications, output beam  2222  is preferably directed towards a substrate  2280  upon which substrate  2280  far-field intensity pattern  2266  is preferably incident. Substrate  2280  may be a workpiece being processed by OPA laser  2202 . For example, OPA laser  2202  may be operative to additively manufacture, cut, weld, sinter or otherwise process workpiece  2280 . Phase control subsystem  2230  preferably varies a phase of the output beam  2222  in order to focus the output beam  2222  on substrate  2280 . It is appreciated that in the absence of the application of such phase variation by phase control subsystem  2230 , output beam  2222  would not be focused on the substrate  2280 . 
     It is a particular feature of a preferred embodiment of the present invention that focal lens  2220  is preferably designed such that the output beam  2222  of OPA laser  2202  in the absence of the application of phase variation thereto, would not be focused by lens  2220  on the surface of substrate  2280 . By way of example, as appreciated from consideration of  FIG.  22 A  illustrating the configuration of output beam  2222  in the absence of the application of phase variation thereto, focal lens  2220  may be optically designed to focus non-phase varied collimated wavefronts  2282  comprising output beam  2222  at a focal point  2284  above a surface of the substrate  2280 . 
     As appreciated from consideration of  FIG.  22 B , illustrating the configuration of output beam  2222  in the case of the application of phase variation thereto, phase-variation of the output beam  2222  preferably serves to modify a shape and hence focus of wavefronts  2282 , as seen in the case of representative phase-modified wavefronts  2286 , which phase-modified wavefronts  2286  are preferably focused on substrate  2280  by way of focal lens  2220 . It is appreciated that the focusing of output beam  2222  on substrate  2280  is thus achieved by phase variation thereof in combination with focal lens  2220 , as illustrated in  FIG.  22 B , rather than solely by focal lens  2220 . 
     As a result of focusing of output beam  2222  on the substrate  2280  being achieved by phase variation thereof, back-scatter arising from substrate  2280  is correspondingly not focused by focal lens  2220  on OPA laser  2202 . As is well known in the art, back-scatter from surfaces treated by laser beams typically returns to the laser and may cause damage thereto, particularly in laser amplification systems. Such damage is avoided in the present invention, due to focal lens  2220  not focusing back-scatter towards OPA laser  2202  and back-scatter therefore not reaching and damaging OPA laser  2202 . 
     An exemplary return path of back-scatter from substrate  2280  towards OPA laser  2202  is illustrated in  FIG.  23   . As seen in  FIG.  23   , back-scattered laser beams  2300  emanating from substrate  2280  preferably arrive at focal lens  2220 . However, back-scattered laser beams  2300  are preferably not focused on OPA laser  2202  by focal lens  2220 , thereby preventing damage thereto. It is understood that should focal lens  2220  be designed to focus non-phase modified laser output from OPA laser  2202  on substrate  2280 , as is typically the case in conventional laser systems, the path of back-scattered beams  2300  would be correspondingly focused by focal lens  2220  on OPA laser  2202 , thus possibly causing damage thereto. 
     It is appreciated that, in certain embodiments of the present invention, the focusing of the output of OPA laser  2202  on substrate  2280  may be performed solely by way of appropriate phase variation of the output beam  2222 , such that focal lens  2220  may be obviated. 
     As described hereinabove with reference to  FIGS.  1 A- 23   , an output from a seed laser may be directed to an amplification system for the amplification thereof. As is well known by those skilled in the art, defects in the laser output by a seed laser feeding an amplification system may result in damage to the amplification system. Typical defects in the laser output by the seed laser responsible for causing damage to an amplification system connected thereto may include reduction of power of the seed laser output and degradation of the laser line width. Resultant damage to the amplification system may occur extremely rapidly, on the order of several nanoseconds, and before the response time of internal sensing mechanisms that may be included in the amplification system. 
     Preferred embodiments of the present invention for preventing damage to an amplification system in the event of failure of a seed laser connected thereto are now described with reference to  FIGS.  24 - 33   . It is understood that the seed laser failure protection systems described hereinbelow may be incorporated in an OPA laser of any of the types described hereinabove with reference to  FIGS.  1 A- 23    or may be incorporated in any other laser system including a seed laser and amplifier connected thereto. 
     Turning now to  FIG.  24   , as seen in  FIG.  24    there is provided a laser system  2400  preferably including a seed laser  2402  providing a laser output and an amplifying subsystem, here embodied by way of example as a power amplifier  2404 , receiving the laser output from seed laser  2402  and amplifying the laser output to provide an amplified laser output  2406 . Laser system  2400  may be embodied, by way of example, a Master Oscillator Power Amplifier (MOPA) laser or may be any other laser system including a seed laser and power amplifier. The laser output from seed laser  2402  preferably reaches power amplifier  2404  via a first optical path  2408 , here embodied, by way of example, as comprising a coiled optical fiber  2410 . 
     In order to detect possible defects in the laser output of seed laser  2402 , system  2400  further preferably includes a detector subsystem, preferably embodied as seed sensor  2420 , receiving the output from seed laser  2402 . The laser output from seed laser  2402  preferably reaches detector subsystem  2420  via a second optical path  2422 . Detector subsystem  2420  may include one or more sensors for sensing properties of the laser output and, more specifically, for detecting possible faults in the laser output. Sensor subsystem  2420  is preferably operatively coupled to power amplifier  2404 . Sensor subsystem  2420  is preferably configured to deactivate power amplifier  2404  upon detection of faults in the laser output from seed laser  2402 . 
     It is a particular feature of a preferred embodiment of the present invention that a first time of flight (TOF=T 1 ) of the laser output along the first optical path  2408  from seed laser  2402  to power amplifier  2404  is greater than a combination of a second time of flight (TOF=T 2 ) of the laser output along the second optical path  2422  from seed laser  2402  to sensor subsystem  2420  and a time taken for sensor subsystem  2420  to deactivate power amplifier  2404 . 
     As a result of the time of flight of the laser output from the seed laser  2402  to the power amplifier  2404  being relatively long, the sensor subsystem  2420  is preferably capable of detecting faults in the laser output received thereat and deactivating the power amplifier  2404  prior to the power amplifier  2404  receiving the faulty laser output, thereby preventing damage to the power amplifier  2404 . 
     Extension of the time of flight of the laser output from the seed laser  2402  to the power amplifier  2404 , in order to allow time for the sensor  2420  to sense faults in the laser output and deactivate the power amplifier  2404  when necessary prior to receipt of the faulty laser output by the power amplifier  2404 , is achieved in the embodiment of the present invention illustrated in  FIG.  24    by inclusion of fiber coil  2410  along the first optical path. By way of example, fiber coil  2410  may have a physical length of 10 km and a time of flight of the laser output therealong may be approximately 50 microseconds. In the case of the development of faults in the output from seed laser  2402 , power amplifier  2404  will therefore continue to receive a non-faulty input signal for the duration of 50 microseconds following the onset of the faulty output signal from seed laser  2402 . 
     The optical path between the seed laser  2402  and the sensor subsystem  2420  does not include coil  2410  and may be a direct and thus far shorter optical path. The time of flight of the laser output from seed laser  2402  to sensor subsystem  2420  is hence preferably much shorter than 50 microseconds, for example of the order of 30 microseconds or less. Following the development of faults in the output from seed laser  2402 , sensor subsystem  2420  thus may rapidly receive the laser output, detect faults therein and switch off power amplifier  2404 , all prior to expiration of the time delay between the seed laser  2402  and the power amplifier  2404 . As a result, power amplifier  2404  is preferably switched off by sensor subsystem  2420  before power amplifier  2404  receives the faulty signal detected by sensor subsystem  2420 , thereby preventing damage to power amplifier  2404 . 
     It is appreciated that the extension of the optical path between the seed laser  2402  and power amplifier  2404 , and hence the increase in the time of flight therealong, in comparison to the optical path time and length between the seed laser  2402  and the sensor subsystem  2420 , is not limited to being achieved by way of inclusion of a fiber coil along the optical path between the seed laser  2402  and power amplifier  2404 . Rather, the optical path between the seed laser  2402  and power amplifier  2404  may be extended by any suitable means, including, for example, the inclusion of an optical delay line  2500  therealong, as illustrated in  FIG.  25   . Furthermore, the optical path between seed laser  2402  and power amplifier  2404  may be a free space optical path  2600 , as illustrated in  FIG.  26   , in which case the time of flight therealong may be extended by use of optical elements such as reflecting mirrors. It is appreciated, however, that the inclusion of coiled fiber  2410  in first optical path  2408  may be particularly advantageous due to the compact configuration thereof and due to the maintenance of the optical mode of the seed laser output by the coiled fiber  2410 . 
     It is appreciated that the particular configuration of coiled fiber  2410  illustrated in  FIG.  24    is representative and exemplary only. Coiled fiber  2410  may be embodied in any suitable form and may be adapted for laser output to travel therealong in a single direction or in a back-and-forth manner so as to further increase the effective length of the optical path provided by coiled fiber  2410 . 
     Reference is now made to  FIG.  27   , which is a simplified schematic diagram of a laser amplifying system including a seed laser failure protection system constructed and operative in accordance with yet another preferred embodiment of the present invention. 
     As seen in  FIG.  27   , there is provided a laser system  2700  preferably including a seed laser  2702  providing a laser output. Seed laser  2702  is preferably connected to a first amplifier  2703 , which first amplifier  2703  is preferably connected in turn to a second amplifier  2704  here embodied by way of example as a power amplifier  2704 , providing an amplified laser output  2706 . Laser system  2700  may be embodied, by way of example, a Master Oscillator Power Amplifier (MOPA) laser or may be any other laser system including a seed laser and power amplifier. 
     As is well known by those skilled in the art, and as detailed hereinabove, defects in the laser output by seed laser  2702  may result in damage to power amplifier  2704 . Typical defects in the laser output by seed laser  2702  causing damage to power amplifier  2704  may include cessation or reduction of power of the seed laser output and degradation of the laser line width. Such damage to the power amplifier may occur extremely rapidly, on the order of several nanoseconds, and before the response time of internal sensing mechanisms that may be included in power amplifier  2704 . 
     In order to avoid damage to power amplifier  2704  as a result of defects in the output of seed laser  2702 , it is a particular feature of a preferred embodiment of the present invention that laser system  2700  includes additional amplifier  2703 . Preferably, additional amplifier  2703  provides far lower amplification than that provided by power amplifier  2704  and is included in system  2700  for the purposes of preventing damage to power amplifier  2704  upon degradation of laser output from seed laser  2702  rather than for the purposes of amplification of the laser output from seed laser  2702  per se. 
     In operation of system  2700 , the laser output from seed laser  2702  is preferably received by first amplifier  2703 . First amplifier  2703  preferably provides a first amplified laser output, which first amplified laser output is preferably received and amplified by second amplifier  2704 . 
     Upon cessation of laser output from seed laser  2702 , due to faulty operation of seed laser  2702 , first amplifier  2703  no longer receives the laser output from seed laser  2702 . In this case, first amplifier  2703  generates amplified spontaneous emission, which amplified spontaneous emission is received by second amplifier  2704 . Alternatively, first amplifier  2703  may be configured such that upon cessation of laser output from seed laser  2702 , first amplifier  2703  begins operating as a laser and generates an additional laser output. 
     It is understood that second amplifier  2704  thus continues to receive an input signal in the form of amplified spontaneous emission or in the form of an additional laser output from first amplifier  2703 , even in the case that seed laser  2702  has ceased to provide a laser output. The amplified spontaneous emission provided by first amplifier  2703  to second amplifier  2704  is sufficient to prevent damage to second amplifier  2704 , which damage would otherwise be likely to occur due to cessation of the provision of a signal thereto. It is understood that system  2700  may additionally include a sensor connected to seed laser  2702  to sense faults in the laser output from seed laser  2702  and deactivate the second amplifier  2704  accordingly. 
     It is appreciated that during proper operation of seed laser  2702 , the first amplification provided by first amplifier  2703  is preferably negligible in comparison to the second, primary amplification provided second amplifier  2704 . 
     As seen in  FIG.  27   , laser output from seed laser  2702  may be fed directly to first amplifier  2703 . Alternatively, as illustrated in  FIG.  28   , additional elements may be inserted interfacing seed laser  2702  and first amplifier  2703 . Particularly, a filter may be inserted between seed laser  2702  and first amplifier  2703  in order to filter out laser beams of unacceptably narrow line width and thus prevent such laser beams from reaching and damaging second amplifier  2704 . 
     A particularly preferred embodiment of a line width filter  2800  suitable for use in the present invention is illustrated in  FIG.  28   . 
     Turning now to  FIG.  28   , filter structure  2800  is seen to be implemented downstream of seed laser  2702  and upstream of first amplifier  2703 . The laser output from seed laser  2702  is preferably split into two parts at a splitter  2805  on entry to filter  2800  and recombined at a recombiner  2806  prior to exit from filter  2800 . A first part of the split laser output from seed laser  2702  preferably travels along a first arm  2807  of filter  2800  between splitter  2805  and recombiner  2806 . A second part of the split laser output from seed laser  2702  preferably travels along a second arm  2808  of filter  2800  between splitter  2805  and recombiner  2806 . As appreciated from a comparison of first and second arms  2807  and  2808 , first arm  2807  preferably includes an additional portion  2809  in comparison to second arm  2808  and thus is longer than second arm  2808 . 
     In the case that the laser output from seed laser  2702  is of unacceptably narrow line width, the laser outputs from first and second arms  2807  and  2808 , when recombined at recombiner  2806 , will mutually interfere due to the relatively high coherence thereof. The recombined beam is preferably detected by a detector  2810 , which detector  2810  is preferably connected to an electronic control module  2811 . Electronic control module  2811  is preferably a coherent beam combining (CBC) card, in operative control of a phase modulator  2812  located along second arm  2808 . Phase modulator  2812  is preferably operated by electronic control card  2811  to alter a phase of the beam along second arm  2808 , such that substantially all of the recombined beam at recombiner  2806  is directed towards detector  2810 . The recombined beam thus does not proceed towards first amplifier  2703  and hence does not reach and cause damage to second amplifier  2704 . The receipt of a laser output from seed laser  2702  by first amplifier  2703  is thereby halted and first amplifier  2703  generates one of amplified spontaneous emission or additional laser output, as detailed hereinabove. 
     In the case that seed laser  2702  is operating properly and the laser output from seed laser  2702  is of acceptably wide line width, the laser outputs from first and second arms  2807  and  2808 , when recombined at recombiner  2806 , will not mutually interfere. This is because the line width is sufficiently wide such that the coherence is relatively low and therefore little or no mutual interference occurs. In this case, a part of the laser output at recombiner  2806  will continue towards first amplifier  2703  and a part of the laser output at recombiner  2806  will be delivered to detector  2810 . The laser output received by first amplifier  2703  is preferably subsequently provided by first amplifier  2703  to second amplifier  2704 , as outlined above with reference to system  2700 . 
     It is understood that the damage protection system illustrated in  FIGS.  27  and  28   , including additional amplifier  2703  and filter structure  2800 , may be employed alone or in combination with any one of the protection systems illustrated in  FIGS.  24 - 26   . 
     Reference is now made to  FIG.  29   , which is a simplified schematic diagram of a laser amplifying system including a seed laser failure protection system constructed and operative in accordance with yet a further preferred embodiment of the present invention. 
     As seen in  FIG.  29   , there is provided a laser system  2900  preferably including a seed laser  2902  providing a first laser output  2903  and an amplifying subsystem, here embodied by way of example as a power amplifier  2904 , receiving the first laser output  2903  from seed laser  2902  and amplifying the laser output to provide an amplified laser output  2906 . Laser system  2900  may be embodied, by way of example, a Master Oscillator Power Amplifier (MOPA) laser or may be any other laser system including a seed laser and power amplifier. 
     In order to detect possible defects in the laser output of seed laser  2902 , system  2900  further preferably includes a detector subsystem, preferably embodied as a seed sensor  2920 , receiving the output from seed laser  2902 . Sensor subsystem  2920  may include one or more sensors for sensing properties of the laser output and, more specifically, for detecting possible faults in the laser output. Sensor subsystem  2920  is preferably operatively coupled to power amplifier  2904 . Sensor subsystem  2920  is preferably configured to deactivate power amplifier  2904  upon detection of faults in the laser output from seed laser  2902 . 
     It is a particular feature of a preferred embodiment of the present invention that laser system  2900  preferably includes an auxiliary laser subsystem, here preferably embodied as an auxiliary seed laser  2930 . Auxiliary seed laser  2930  preferably provides a second laser output  2932  to amplifier  2904 , which second laser output  2932  is preferably of a significantly lower power than a power of first laser output  2903 . By way of example only, first laser output  2903  may have a first power in the range of 80-100 milliwatts whereas second laser output  2932  may have a second power in the range of 50-70 milliwatts. 
     Auxiliary seed laser  2930  preferably provides second laser output  2932  at least upon cessation of seed laser  2902  providing first laser output  2903  to amplifier  2904 . Particularly preferably, auxiliary seed laser  2930  preferably operates continuously so as to provide second laser output  2932  to amplifier  2904  both concurrently with seed laser  2902  providing first laser output  2903  thereto as well as upon cessation of seed laser  2902  providing first laser output  2903 . 
     During proper operation of seed laser  2902 , amplifier  2904  preferably receives both first laser output  2903  from seed laser  2902  and second laser output  2932  from auxiliary seed laser  2930 . Due to the power of second laser output  2932  being significantly lower than the power of first laser output  2903 , the contribution of second laser output  2903  to amplified laser output  2906  is preferably negligible. Preferably, although not necessarily, second laser output  2932  is of a different wavelength than first laser output  2903 , in order for further reduce the influence of second laser output  2932  on amplified laser output  2906 . By way of example only, first laser output  2903  may have a first wavelength in the range of 1060-1070 nm whereas second laser output  2932  may have a second wavelength in the range of 1070-1080 nm. 
     Upon cessation of laser output from seed laser  2902 , due to faulty operation of seed laser  2902  as sensed by sensor subsystem  2920 , sensor subsystem  2920  is preferably operative to deactivate amplifier  2904 . Due to the finite response time of amplifier  2904  and detector subsystem  2920 , amplifier  2904  is not instantaneously deactivated but rather continues to operate for a finite period of time following cessation of laser output from seed laser  2902 . It is understood that during this time, amplifier  2904  no longer receives first laser output  2903  from seed laser  2902 . However, auxiliary seed laser  2930  preferably continues to provide second laser output  2932  to amplifier  2904 . It is understood that amplifier  2904  thus continues to receive an input signal in the form of second laser output  2932 , even in the case that seed laser  2902  has ceased to provide a laser output. The second laser output  2932  provided by auxiliary seed laser  2930  to amplifier  2904  is sufficient to prevent damage to amplifier  2904 , which damage would otherwise be likely to occur due to cessation of the provision of a signal thereto, prior to amplifier  2904  being deactivated by sensor  2920 . 
     Reference is now made to  FIG.  30   , which is a simplified schematic diagram of a laser amplifying system including a seed laser failure protection system constructed and operative in accordance with a still further preferred embodiment of the present invention. 
     As seen in  FIG.  30   , there is provided a laser system  3000  preferably including a seed laser  3002  providing a first laser output  3003  and an amplifying subsystem, here embodied by way of example as a power amplifier  3004 , receiving the first laser output  3003  from seed laser  3002  and amplifying the laser output to provide an amplified laser output  3006 . Laser system  3000  may be embodied, by way of example, a Master Oscillator Power Amplifier (MOPA) laser or may be any other laser system including a seed laser and power amplifier. 
     In order to detect possible defects in the laser output of seed laser  3002 , system  3000  further preferably includes a detector subsystem  3020  receiving the output from seed laser  3002 . Detector subsystem  3020  may include one or more sensors for sensing properties of the laser output and, more specifically, for detecting possible faults in the laser output. Sensor subsystem  3020  is preferably operatively coupled to power amplifier  3004 . Sensor subsystem  3020  is preferably configured to deactivate power amplifier  3004  upon detection of faults in the laser output from seed laser  3002 . 
     It is a particular feature of a preferred embodiment of the present invention that laser system  3000  preferably includes a pair of gratings  3030 . Pair of gratings  3030  preferably includes a first reflection grating  3032  preferably positioned at an entry  3034  of amplifier  3004  and a second reflection grating  3036  preferably positioned at an exit  3038  of amplifier  3004 . Pair of gratings  3030  in combination with amplifier  3004  preferably form a preferred embodiment of an auxiliary laser subsystem  3040 . 
     During proper operation of seed laser  3002 , amplifier  3004  preferably receives first laser output  3003  from seed laser  3002  and amplifies first laser output  3003  to provide amplified laser output  3006 . 
     Upon cessation of laser output from seed laser  3002 , due to faulty operation of seed laser  3002  as sensed by sensor subsystem  3020 , sensor subsystem  3020  is preferably operative to deactivate amplifier  3004 . Due to the finite response time of amplifier  3004  and sensor subsystem  3020 , amplifier  3004  is not instantaneously deactivated but rather typically continues to operate for a finite period of time following cessation of laser output from seed laser  3002 . It is understood that during this time, amplifier  3004  no longer receives a laser output from seed laser  3002 . In this case, reflection gratings  3030  preferably provide a signal feedback to amplifier  3004 , such that amplifier  3004  in combination with pair of gratings  3030  preferably begins to operate as a laser. Reflection gratings  3030  preferably have a relatively low reflectance such that the signal feedback provided by reflection gratings  3030  is of lower power than the power of the laser output  3003  of seed laser  3002 . 
     Particularly preferably, although not necessarily, pair of gratings  3030  are reflective at a wavelength different than the wavelength of the first laser output  3003  of seed laser  3002 , such that during proper operation of seed laser  3002  gratings  3030  have negligible influence on amplified output  3006 . By way of example only, first laser output  3003  may have a wavelength in the range of 1060-1070 nm whereas gratings  3030  may be reflective at a wavelength in the range of 1090-1100 nm. 
     It is understood that amplifier  3004  thus continues to receive an input signal in the form of signal feedback from gratings  3030 , even in the case that seed laser  3002  has ceased to provide a laser output. As a result, amplifier  3004  in combination with gratings  3030  begins to operate as a laser upon cessation of operation of seed laser  3002 , thereby preventing damage to amplifier  3004 , which damage would otherwise be likely to occur due to cessation of the provision of a signal thereto. 
     As seen in  FIGS.  29  and  30   , laser output from seed lasers  2902 ,  3002  may be fed directly to amplifiers  2904 ,  3004  respectively. Alternatively, as illustrated in  FIGS.  31  and  32   , additional elements may be inserted interfacing the seed laser and amplifier. Particularly, a line width filter, such as filter  2800  or any other suitable filter, may be inserted between seed lasers  2902 ,  3002  and amplifiers  2904 ,  3004  respectively in order to filter out laser beams of unacceptably narrow line width and thus prevent such laser beams from reaching and damaging amplifiers  2904 ,  3004 . 
     As detailed hereinabove, each of the laser systems described with reference to  FIGS.  24 - 32    may include a detector subsystem, such as detector subsystem  2420 ,  2920  and  3020 . The detector subsystem is preferably embodied as at least one sensor for sensing the output from the seed laser. A particularly preferred embodiment of a sensor forming a part of a detector subsystem such as detector subsystem  2420 ,  2920  and  3020  is illustrated in  FIG.  33   . It is appreciated, however, that the sensor illustrated in  FIG.  33    is not limited to use in systems of the type described herein and may be incorporated as a laser output sensor in any laser system benefitting from the use thereof. 
     As seen in  FIG.  33   , there is provided a detector subsystem  3320 . Laser output from a seed laser preferably enters sensor subsystem  3320  at an input point  3330  and travels towards a splitter  3334 . At splitter  3334 , a small portion such as 1% of the laser output is directed towards a detector  3336  and the remaining portion of the laser output continues towards a sensor amplifier  3340 . Sensor amplifier  3340  is preferably a lower power amplifier than power amplifier  2404 ,  2704 ,  2904  or  3004 . Sensor amplifier  3340  preferably outputs an amplified laser output, which amplified laser output is preferably delivered to an additional detector  3342  by way of an elongate optical fiber  3344 . 
     In operation of detector subsystem  3320 , in the case that the output from the seed laser ceases, the intensity of the amplified laser output detected at additional detector  3342  decreases. In this case, a control module (not shown) connected to additional detector  3342  as well as to a power amplifier such as power amplifier  2404 ,  2704 ,  2904  or  3004  may deactivate the power amplifier in order to prevent damage thereto. 
     In the case that the output from the seed laser degrades so as to have an unacceptably narrow line width, non-linear effects will be initiated in fiber  3344 . It is appreciated that fiber  3344  is advantageously configured so as to be as sensitive as possible to such non-linear effects. For this purpose, fiber  3344  is preferably of considerable length and preferably has a small core diameter, in order to increase the sensitivity of fiber  3344  to the line width of the laser output from the seed laser. By way of example only, fiber  3344  may have a length of approximately 25 m and a core diameter of approximately 6 microns. 
     Due to the non-linear effects initiated in fiber  3344  upon narrowing of the line width of the output from the seed laser, fiber  3344  preferably begins to operate as a mirror, reflecting light backwards towards amplifier  3340 . As a result of the reflected light returning to amplifier  3340 , an increased signal reaches splitter  3334  and is detected by detector  3336 . Upon detection of an increased signal at detector  3336 , the power amplifier is preferably deactivated in order to prevent damage thereto. 
     It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly claimed hereinbelow. Rather, the scope of the invention includes various combinations and subcombinations of the features described hereinabove as well as modifications and variations thereof as would occur to persons skilled in the art upon reading the forgoing description with reference to the drawings and which are not in the prior art.