Patent ID: 12261406

DETAILED DESCRIPTION

FIGS.1through5, described below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any type of suitably arranged device or system.

For simplicity and clarity, some features and components are not explicitly shown in every figure, including those illustrated in connection with other figures. It will be understood that any features illustrated in the figures may be employed in any of the embodiments described. Omission of a feature or component from a particular figure is for purposes of simplicity and clarity and is not meant to imply that the feature or component cannot be employed in the embodiments described in connection with that figure.

As noted above, various laser systems are being developed for a number of commercial and defense-related applications, such as to direct high-energy laser (HEL) beams at incoming missiles, rockets, mortars, or other targets. Unfortunately, various factors can degrade an HEL beam or other laser beam or interfere with its use. For example, jitter refers to movement of an HEL beam or other laser beam on a target, which can prevent the beam from remaining at the same location on the target. This typically increases the amount of time needed for the beam to achieve a desired result, such as damaging or destroying the target, or it can prevent the desired result from being achieved altogether.

To help overcome these or other problems, an auto-alignment beam that is co-boresighted to an HEL beam can be generated, which means that the auto-alignment beam is (ideally) aimed at the same point as the HEL beam. As a result, the auto-alignment beam can be used to aim the HEL beam at a target before the HEL beam is actually generated and directed towards the target. This may be referred to as low-power aiming of the HEL beam. Also, the auto-alignment beam can be used to sense jitter or other movement of the auto-alignment beam, and corrections can be made to one or more optical devices to substantially cancel the movement of the auto-alignment beam. Since the auto-alignment beam is co-boresighted to the HEL beam, this (ideally) also substantially cancels the movement of the HEL beam on a target. The wavelength of the auto-alignment beam can be selected to be far out-of-band relative to the HEL beam, which helps to split the auto-alignment beam from the HEL beam for detection of the auto-alignment beam.

Unfortunately, in certain systems, an auto-alignment beam is generated downstream from an HEL beam, which means that the HEL beam and the auto-alignment beam are generated separately and then optically combined onto a common optical path. In these or other types of systems, the auto-alignment beam cannot follow part of an optical path that is followed by the HEL beam, and one or more optical elements in the optical path of the HEL beam (prior to optical combination with the auto-alignment beam) are not sampled using the auto-alignment beam. Because of this, boresight shifts due to motion of the HEL beam relative to the auto-alignment beam can occur, so the HEL beam can move in a way that the auto-alignment beam does not. This results in the creation of boresight errors or pointing errors that cause the aimpoint of the auto-alignment beam to diverge from the aimpoint of the HEL beam. These boresight errors can be caused by various factors, such as thermally-induced motion or structurally-induced motion of the optical element or elements that are not sampled using the auto-alignment beam. These boresight errors can result in relative jitter between the auto-alignment beam and the HEL beam and jitter of the HEL beam on the target, which reduces the effective power of the HEL beam on a target.

In accordance with this disclosure, an auto-alignment laser that generates an auto-alignment beam is embedded into or otherwise used in conjunction with an array or other collection of lasers that generate multiple input laser beams. The input laser beams and the auto-alignment beam are provided to a diffraction grating. The wavelengths of the input laser beams and the angles of the input laser beams on the diffraction grating are selected so that the diffraction grating combines the input laser beams to produce an HEL beam or other combined laser beam having a higher power or energy (relative to the multiple input laser beams individually). Moreover, the wavelength of the auto-alignment beam and the angle of the auto-alignment beam on the diffraction grating are selected so that the diffraction grating causes a diffraction (such as a second-order or other higher-order diffraction) of the auto-alignment beam to be co-boresighted to the HEL beam or other combined laser beam. Because of this, the auto-alignment beam can follow the same optical path as the HEL beam or other combined laser beam through a laser system, at least up to the point where the auto-alignment beam is split from the combined laser beam and processed. To support this, the wavelength of the auto-alignment beam is selected so that the second-order or other higher-order diffraction of the auto-alignment beam co-propagates with the combined beam.

In this way, the auto-alignment beam can share more of the optical path of an HEL beam or other combined laser beam through a laser system. This reduces or eliminates the presence of optical elements in the laser system that are not sampled using the auto-alignment beam. Because of this, motion of the HEL beam or other combined beam relative to the auto-alignment beam can be reduced or minimized, which reduces or minimizes boresight errors. As a result, the aimpoint of the combined beam can more effectively track the aimpoint of the auto-alignment beam, even in the presence of thermally-induced motion or structurally-induced motion of one or more optical elements in the laser system. This enables more effective aiming of the combined beam at a target with improved fidelity and improved tracking and jitter correction. Overall, this can result in reduced or minimal movement of the combined beam on a target, increasing the effective power of the combined beam on the target.

FIG.1illustrates an example system100that includes a spectral beam combiner supporting an embedded auto-alignment scheme according to this disclosure. As shown inFIG.1, the system100includes a high-energy laser system102that is being used to engage a target104. The target104in this example represents a rocket or missile. However, the high-energy laser system102may be used with any other suitable targets, such as one or more targets on the ground, in the air, or in space. Also, a spectral beam combiner supporting an embedded auto-alignment scheme may be used in any other suitable laser system for any other suitable purpose and is not limited to use with high-energy laser systems that engage hostile targets.

The laser system102in this example generates an HEL beam106. The HEL beam106represents a beam of laser energy that typically has a high power or energy level, such as at least about 10 kilo-Watts (kW) of power. Often times, the HEL beam106is ideally focused to as small an area as possible on the target104, which is done in order to achieve the maximum possible effect on the target104. However, because of this, the HEL beam106is particularly susceptible to jitter or other non-consistent placement of the HEL beam106on the target104.

As described in more detail below, the laser system102includes a spectral beam combiner having an auto-alignment laser embedded or otherwise used in conjunction with an array or other collection of other lasers. The auto-alignment laser is configured to generate an auto-alignment beam, and the collection of other lasers is configured to generate multiple input laser beams. A diffraction grating combines the input laser beams to produce the HEL beam106, and the diffraction grating causes a portion of the auto-alignment beam to co-propagate with the HEL beam106within the laser system102. Thus, the auto-alignment beam follows the same optical path as the HEL beam106, at least until split from the HEL beam106for sensing. This reduces or minimizes motion of the HEL beam106relative to the auto-alignment beam within the laser system102and therefore reduces or minimizes boresight errors.

In this particular example, the laser system102includes or is used with a multi-axis gimbal108, which mounts the laser system102on a vehicle110. The multi-axis gimbal108includes any suitable structure configured to point the laser system102in a desired direction. In some embodiments, the multi-axis gimbal108can rotate the laser system102about a vertical axis for azimuth control and about a horizontal axis for elevation control. However, any other suitable mechanisms for pointing the laser system102(such as about a single axis or multiple axes) may be used here. Also, in this particular example, the vehicle110on which the laser system102is mounted represents an armored land vehicle. However, the laser system102may be used with any other suitable type of vehicle (such as any other suitable land, air, or space vehicle), or the laser system102may be mounted to a fixed structure (such as a building).

Among other things, the functionality implemented within the laser system102that is described in this patent document helps to reduce or minimize beam jitter or other movement of the HEL beam106on the target104. The ability to maintain the HEL beam106at substantially the same position on the target104can help increase the effectiveness of the laser system102. For example, reduced or minimal movement of the HEL beam106on the target104can help to increase the effective power of the HEL beam106on the target104. A reduction of even a few microradians of jitter on the target104can make a large difference in the effectiveness of the HEL beam106on the target104. As a particular example, if an HEL beam106normally experiences about 4.4 microradians of jitter on the target104without the functionality described in this patent document, reducing the jitter to effectively zero with the functionality described in this patent document may double the effectiveness of the HEL beam106on the target104.

AlthoughFIG.1illustrates one example of a system100that includes a spectral beam combiner supporting an embedded auto-alignment scheme, various changes may be made toFIG.1. For example, the laser system102may be used in any other suitable environment and for any other suitable purpose. Also, while the use of an auto-alignment beam co-propagating with an HEL beam106is described here, the same or similar functionality can be used to allow an auto-alignment beam to co-propagate with any other suitable laser beam (whether or not that other beam is technically considered a “high-power” beam). In addition, while shown here as being used to damage or destroy a moving hostile target104, the laser system102can be used in any number of other ways depending on the application.

As noted above, there are various commercial and other non-defense-related applications for high-energy laser systems that may benefit from the approaches described in this patent document. For instance, in commercial mining applications like drilling, mining, or coring operations, a high-energy laser can be used to soften or weaken an earth bed prior to drilling, which may allow for fewer drill bit changes and extended lifetimes and reliabilities of drill bits. In remote laser welding, cutting, drilling, or heat treating operations like industrial or other automation settings, a high-energy laser can be used to allow for the processing of thicker materials at larger working distances from the laser system while minimizing the heat-affected zone and maintaining vertical or other cut lines. This helps to support welding or cutting operations where proximity to the weld or cut site is difficult or hazardous and helps to protect the laser system and possibly any human operators from smoke, debris, or other harmful materials. In construction and demolition operations like metal resurfacing or deslagging, paint removal, and industrial demolition operations, a high-energy laser can be used to ablate material much faster and safer compared to conventional operations. As a particular example of this functionality, a high-energy laser can be used to support demolition of nuclear reactors or other hazardous structures, such as by cutting through contaminated structures like contaminated concrete or nuclear containment vessels or reactors from long distances. This avoids the use of water jet cutting or other techniques (which creates contaminated water or other hazardous waste) and provides improved safety (since human operators can remain farther away from contaminated structures being demolished). A number of additional applications are possible, such as with a high-energy laser in power beaming applications (where a beam is targeted to photovoltaic cells of remote devices to be recharged) or hazardous material applications (where a beam is used to heat and decompose hazardous materials into less harmful or non-harmful materials).

FIG.2illustrates a portion of an example high-energy laser system102that includes a spectral beam combiner supporting an embedded auto-alignment scheme according to this disclosure. For ease of explanation, the high-energy laser system102shown inFIG.2may be described as being used in the system100ofFIG.1to engage a hostile target104. However, the high-energy laser system102ofFIG.2may be used in any other suitable environment and for any other suitable purpose.

As shown inFIG.2, the high-energy laser system102includes various components that are used to generate the HEL beam106. In this example embodiment, the high-energy laser system102includes multiple input lasers202a-202d, which generally operate to produce different input laser beams204a-204d. Each input laser beam204a-204drepresents a beam of optical energy, and the input laser beams204a-204dare combined as described below to produce the HEL beam106(or some other combined beam). Also as described below, each input laser beam204a-204dmay have a slightly different wavelength in order to facilitate combination of the input laser beams204a-204dto produce the HEL beam106. In some embodiments, the input laser beams204a-204dmay have wavelengths around a nominal value of about 1050 nm, although other wavelengths may be used.

Each input laser202a-202drepresents any suitable structure configured to generate a beam of laser energy. In some embodiments, each input laser202a-202dincludes a planar waveguide (PWG) amplifier or other optical amplifier, which amplifies a seed laser beam using pump power provided to the optical amplifier by one or more pump sources (such as one or more laser diode arrays) to produce a corresponding input laser beam204a-204d. However, any other suitable laser may be used here for each input laser202a-202d. Also, each of the input laser beams204a-204dmay have any suitable power or energy level, such as at least about 2.5 kW of power. Note that while four input lasers202a-202dare shown here as producing four input laser beams204a-204d, the laser system102may include any suitable number of input lasers that produce any suitable number of input laser beams. The number of input lasers202a-202dmay vary based on, for instance, the desired power or energy level of the HEL beam106.

The high-energy laser system102also includes an auto-alignment laser206, which generally operates to produce an auto-alignment laser beam208. The auto-alignment laser beam208represents a beam of optical energy, which is lower (and typically much lower) in power or energy compared to the input laser beams204a-204d. The auto-alignment laser beam208is used as described below to help aim the HEL beam106and to sense jitter or other movement that affects the auto-alignment laser beam208and therefore the HEL beam106. The auto-alignment laser206represents any suitable structure configured to generate a beam of laser energy. In some embodiments, the auto-alignment laser206represents a laser operating around about 525 nm. However, any other suitable laser may be used here as the auto-alignment laser206.

The various optical beams204a-204d,208from the input lasers202a-202dand the auto-alignment laser206are provided to a fiber launcher210. The input lasers202a-202dand the auto-alignment laser206may be coupled to the fiber launcher210in any suitable manner, such as via one or more optical fibers. The distance between the lasers202a-202d,206and the fiber launcher210can vary as needed or desired, although in some implementations the distance may be kept as small as possible. Also, depending on the implementation, the auto-alignment laser206may be embedded with the input lasers202a-202din the same structure, or the auto-alignment laser206may be implemented separate from the input lasers202a-202d. In some embodiments, the lasers202a-202d,206may be formed as an array of lasers in an integrated structure, and the auto-alignment laser206can be embedded with the input lasers202a-202din the array.

The fiber launcher210receives the input beams204a-204dand the auto-alignment beam208and launches or provides the beams204a-204d,208to a transform optic212. For example, the fiber launcher210can receive the beams204a-204d,208and output the beams in specific directions towards the transform optic212through free space. The fiber launcher210includes any suitable structure configured to output multiple optical beams in a desired manner.

The transform optic212operates to receive the launched beams204a-204d,208from the fiber launcher210and to transform the beams204a-204d,208. In this example, the transform optic212is configured to focus the beams204a-204d,208onto a diffraction grating214. This can be accomplished using a concave reflective surface of the transform optic212. The transform optic212includes any suitable reflective structure or other optical device(s) configured to focus or otherwise provide the beams204a-204d,208to the diffraction grating214in a specified manner.

The diffraction grating214generally represents an optical device that has a periodic structure. The periodic structure of the diffraction grating214causes optical energy in each of the beams204a-204d,208to split or diffract and travel in different directions from the diffraction grating214. Diffraction gratings can be reflective or transmissive, and the diffraction grating214in this example is reflective (although a transmissive diffraction grating may also be used depending on the implementation). As described in more detail below, the splitting or diffracting of each beam204a-204d,208is dependent (at least in part) on the wavelength of the optical energy in the beam204a-204d,208and the direction at which the beam204a-204d,208reaches the diffraction grating214. This feature of the diffraction grating214is used to combine the input laser beams204a-204dto produce the HEL beam106. This feature of the diffraction grating214is also used to make a diffraction (such as a second-order or other higher-order diffraction) of the auto-alignment beam208co-propagate with the HEL beam106, which essentially causes the auto-alignment beam208to be co-boresighted to the HEL beam106.

Since the diffracting of each beam204a-204d,208varies based on the wavelength of the optical energy in the beam204a-204d,208and the direction that the beam204a-204d,208reaches the diffraction grating214, this feature can be used to select or control how the beams204a-204d,208are processed prior to reaching the diffraction grating214. Here, the input laser beams204a-204dare being combined to produce the HEL beam106. As a result, the wavelength and direction of each input laser beam204a-204dare selected or controlled so that most optical energy from all of the input laser beams204a-204ddiffracts from the diffraction grating214in the same direction. Because the input laser beams204a-204dhere arrive at the diffraction grating214from slightly different directions, the wavelengths of the input laser beams204a-204dcan be selected so that the diffracted optical energy from the input laser beams204a-204dleaves the diffraction grating214in the same direction. In this way, the diffraction grating214combines most of the optical energy from all of the input laser beams204a-204dto produce a combined beam having a higher power or energy than the input laser beams204a-204dindividually. In this example, the combined beam represents the HEL beam106, although other implementations may produce other combined beams.

The diffraction grating214operates similarly with respect to the auto-alignment beam208. The diffraction grating214diffracts the auto-alignment beam208so that part of the auto-alignment beam208(referred to as an auto-alignment beam208a) co-propagates with the HEL beam106and at least one other part of the auto-alignment beam208(referred to as an auto-alignment beam208b) does not. Again, the wavelength and direction of the auto-alignment beam208are selected or controlled so that the auto-alignment beam208adiffracts from the diffraction grating214in the same direction as the HEL beam106. In this way, the diffraction grating214allows the auto-alignment beam208ato co-propagate with the combined beam (the HEL beam106). Essentially, the various components210-214form a spectral beam combiner that combines optical energy at varying wavelengths to form a combined beam having a higher power or energy than the individual input beams with a co-propagating auto-alignment beam.

As can be seen here, the selection of the wavelength used for the auto-alignment beam208affects how the auto-alignment beam208diffracts from the diffraction grating214. Thus, the wavelength used for the auto-alignment beam208can be selected for a particular implementation of the laser system102in order to provide the desired diffraction of the auto-alignment beam208from the diffraction grating214and proper co-propagation of the auto-alignment beam208awith the HEL beam106. In some embodiments, this is accomplished by identifying the wavelength of the auto-alignment beam208that is needed so that the second-order diffraction (or some other higher-order diffraction) of the auto-alignment beam208from the diffraction grating214co-propagates with the HEL beam106. A higher-order diffraction represents a diffraction of the second-order or higher (whether positive or negative).

In particular embodiments, the auto-alignment beam208may have a wavelength that is roughly half the wavelengths of the input beams204a-204d. While the input beams204a-204dhave different wavelengths, these wavelengths may typically be relatively close to one another. For example, the input laser beams204a-204dmay have different wavelengths that are all within a small range, such as within one or several nanometers of a nominal value of about 1050 nm (depending on the angles of the input laser beams204a-204don the diffraction grating214). In these embodiments, the auto-alignment beam208may have a wavelength that is roughly half the wavelengths of the input laser beams204a-204d, meaning around 525 nm. Note, however, that other wavelengths can be used here.

In some embodiments, the specific wavelength of the auto-alignment beam208can be calculated as one-half the wavelength that would have been used if the auto-alignment beam208represented another input laser beam being combined to produce the HEL beam106. That is, assume the auto-alignment laser206is replaced by an additional input laser that generates an additional input laser beam, which is diffracted by the diffraction grating214for inclusion in the HEL beam106. Based on the angle of arrival of the additional input laser beam at the diffraction grating214, the additional input laser beam would require a specific wavelength in order to be diffracted in the same direction as the other input laser beams204a-204din order to form the HEL beam106. Whatever that specific wavelength is, the auto-alignment beam208may have exactly one-half of that specific wavelength. This wavelength selection causes the second-order or other higher-order diffraction of the auto-alignment beam208from the diffraction grating214to co-propagate with the HEL beam106. Thus, for instance, if the additional input laser beam in the position of the auto-alignment beam208needs a wavelength of 1050.66 nm to be diffracted properly in order to form part of the HEL beam106, the auto-alignment beam208may have a wavelength of 525.33 nm. Note, however, that other wavelengths and angles may be used for the auto-alignment beam208(and/or for one, some, or all of the input beams204a-204d) in order to achieve the desired co-propagation of the auto-alignment beam208awith the HEL beam106.

One or more beam dumps216may be used to terminate diffracted portions of the beams204a-204d,208that are not used to form the HEL beam106or the auto-alignment beam208a. Each beam dump216includes any suitable structure configured to absorb or otherwise terminate optical energy. In some embodiments, for example, each beam dump216represents an absorptive structure that absorbs optical energy at the desired wavelength(s) and that converts the optical energy into thermal energy, as well as a cooling system that removes the thermal energy to cool the absorptive structure. Beam dumps can come in a wide variety of configurations, and this disclosure is not limited to any particular type of beam dump. Note that since the directions of diffraction from the diffraction grating214depend on the wavelengths of the beams204a-204d,208, multiple beam dumps216may be used here in different directions from the diffraction grating214, or a single large beam dump216may be sized and shaped to absorb all of the diffracted optical energy from the beams204a-204d,208that is not being further used in the laser system102.

Fold mirrors218,220,222are used to redirect the HEL beam106and the co-propagating auto-alignment beam208a. Each fold mirror218,220,222includes any suitable reflective structure configured to reflect laser beams in a desired direction. The reflected beams106,208aare received at a fast steering mirror224. The fast steering mirror224is configured to be controlled in order to alter how the beams106,208areflect from the fast steering mirror224. Depending on the implementation, the fast steering mirror224may be rotated or moved forwards or backwards as needed to control the reflection of the beams106,208a. The fast steering mirror224includes any suitable reflective structure configured to reflect laser beams in a controllable direction. The fast steering mirror224typically includes at least one servo for controlling how the laser beams are directed.

A beam splitter226reflects all or the bulk of the HEL beam106(and optionally part of the auto-alignment beam208a) through an exit aperture228. This allows at least the bulk of the HEL beam106to be transmitted in a desired direction, such as towards a target104. Note that the HEL beam106that passes through the exit aperture228may be further processed if needed or desired before being transmitted towards a target104or other destination. For instance, the bulk of the HEL beam106passing through the exit aperture228may be provided to a telescope that is used to focus the HEL beam106on a target104. The telescope may also be used to receive reflected optical energy from the target104, and the reflected optical energy may be processed and imaged using one or more image sensors (such as a short-wave infrared or “SWIR” camera or other imaging device or devices). Of course, at least the bulk of the HEL beam106passing through the exit aperture228may be used in any other suitable manner and for any other suitable purpose.

The beam splitter226also transmits at least a portion of the auto-alignment beam208aand optionally a small portion (usually a very small portion) of the HEL beam106to at least one sensor230. The sensor230can process the received beam or beams to identify the position(s) of at least one of the auto-alignment beam208aand the HEL beam106, such as absolute positions on the sensor230or relative positions with respect to each other. The output of the sensor230may be used to perform various functions, such as adjustment of the fast steering mirror224. Each sensor230includes any suitable structure configured to sense at least one optical beam, such as a Coude Optical Position Sensor (COPS) far-field sensor or other position sensitive detector (PSD).

In some embodiments, the laser system102includes at least one controller232, which controls the overall operation of the laser system102and possibly a larger system into which the laser system102is integrated. For example, the controller232can control the operation of the lasers202a-202d,206in order to control the generation of the beams106,208. The controller232can also process data from various sensors, such as the sensor230, in order to alter one or more optical devices or other components in the laser system102. As a particular example, the controller232can process measurements from the sensor230and possibly other sensors and adjust operation of the fast steering mirror224in order to help stabilize the HEL beam106on a target104.

In some embodiments, the controller232includes at least one processor234, at least one memory236, and at least one communication interface238. The at least one processor234may be configured to execute instructions stored in and obtained from at least one memory236. The at least one processor234may include any suitable number(s) and type(s) of processing devices or other computing or control devices in any suitable arrangement. As specific examples, the at least one processor234may include one or more microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), application specific integrated circuits (ASICS), or discrete circuitry. The at least one memory236may include any suitable number(s) and type(s) of data storage and retrieval devices, such as random access memory, read only memory, Flash memory, a hard drive, an optical drive, or other memory. The at least one communication interface238may include any suitable number(s) and type(s) of interfaces allowing communication with other components of the laser system102or a larger system, such as one or more wired or wireless interfaces. Note that while shown and described as having a single controller232, the laser system102may include multiple controllers that are used to control different aspects of the laser system102.

As can be seen in the example shown inFIG.2, the auto-alignment beam208follows the same optical path as the input beams204a-204dand subsequently the HEL beam106from the fiber launcher210to the beam splitter226. As a result, all of the optical components212,214,218,220,222,224, and226) can be sampled using the auto-alignment beam208, and there are no components here that can create relative motion between the auto-alignment beam208and the HEL beam106that is not sensed through the use of the auto-alignment beam208. As a result, all thermally-induced motion, structurally-induced motion, or other motion of the optical components are identifiable using the auto-alignment beam208, which can help to reduce or eliminate jitter error associated with unsampled optical elements in the path of the HEL beam106.

AlthoughFIG.2illustrates a portion of one example of a high-energy laser system102that includes a spectral beam combiner supporting an embedded auto-alignment scheme, various changes may be made toFIG.2. For example, the makeup and arrangement of the laser system102shown inFIG.2are for illustration only. Components can be added, omitted, combined, further subdivided, replicated, or placed in any other suitable configuration according to particular needs. As a particular example, multiple auto-alignment lasers206may be used to generate multiple auto-alignment laser beams208, and one, some, or all of the auto-alignment laser beams208may have suitable wavelengths so that their second-order or other higher-order diffractions from the diffraction grating214are co-boresighted with the HEL beam106. As another particular example, the arrangement of a transform optic, various mirrors, a splitter, and other optical devices inFIG.2to process and route optical beams may be based on specific implementation needs, and other arrangements of optical devices may be used to process and direct optical beams in the desired manner. Also, the number(s) and type(s) of mirrors and other optical devices can vary based on the specific needs in a laser system. In general, this disclosure is not limited to any specific arrangement of mirrors and other optical devices.

FIG.3illustrates an example diffraction grating214for use in a spectral beam combiner supporting an embedded auto-alignment scheme according to this disclosure. For ease of explanation, the diffraction grating214shown inFIG.3may be described as being used in the laser system102ofFIG.2within the system100ofFIG.1to engage a hostile target104. However, the diffraction grating214ofFIG.3may be used in any other suitable laser system designed in accordance with this disclosure that operates within any other suitable environment and for any other suitable purpose.

A diffraction grating214is generally defined as an optical surface or volume that produces a periodic modulation of an incident wavefront, typically through either index-of-refraction variations within the diffraction grating214or surface-relief variations on a surface of the diffraction grating214. In the example shown inFIG.3, a diffraction grating214includes a surface302having surface-relief variations that are periodic. In this particular example, the surface302has sawtooth surface-relief variations that are defined by angled surfaces304and surfaces306that are substantially parallel to a normal line308(which is perpendicular to the overall surface302). It should be noted that this particular periodic surface structure is for illustration only and that other diffraction gratings can have other periodic surface-relief variations (or, as noted above, index-of-refraction variations). This disclosure is not limited to any specific type or implementation of diffraction grating214. In this example, the surface features of the surface302have a period310(denoted A) that defines the regular distance between periodic features on the surface302. In this example, the period is defined by the peaks of the periodic features, although the period can be defined as the distance between any common points of the surface features.

FIG.4illustrates an example operation of a diffraction grating214in a spectral beam combiner supporting an embedded auto-alignment scheme according to this disclosure. For ease of explanation, the diffraction grating214shown inFIG.4may be described as being used in the laser system102ofFIG.2within the system100ofFIG.1to engage a hostile target104. However, the diffraction grating214ofFIG.4may be used in any other suitable laser system designed in accordance with this disclosure that operates within any other suitable environment and for any other suitable purpose.

As shown inFIG.4, an incoming optical beam402is received at the diffraction grating214. The optical beam may, for example, represent any of the beams204a-204d,208described above. The optical beam402is incident on the diffraction grating214at an angle that is denoted θi. In this example, the optical beam402diffracts from the grating214into different diffracted beams404a-404d. While four diffracted beams404a-404dare shown here, there may be other numbers of diffracted beams generated here. The diffraction is due to the index-of-refraction variations within the diffraction grating214or the surface-relief variations on a surface of the diffraction grating214, such as is shown inFIG.3.

The diffraction grating214disperses the optical energy in the beam402through a combination of diffraction and interference. Here, each of the beams404a-404ddiffracts from the diffraction grating214at an angle that is denoted θd, and the diffraction angle θddiffers for each of the different diffraction beams404a-404d. As noted above, a diffraction grating214may be transmissive rather than reflective as is shown inFIG.4, although the same general principles apply to a transmissive diffraction grating.

In some embodiments, the beams404a-404drepresent different diffractions of the optical beam402from the diffraction grating214, where the order of each diffraction of the optical beam402is denoted m. For example, the beam404amay be said to represent the positive second-order diffraction of the beam402, meaning m equals +2. The beam404bmay be said to represent the positive first-order diffraction of the beam402, meaning m equals +1. The beam404cmay be said to represent the negative first-order diffraction of the beam402, meaning m equals −1. The beam404dmay be said to represent the negative second-order diffraction of the beam402, meaning m equals −2. A line406here represents the expected reflection angle of the beam402if the diffraction grating214had a completely reflective planar surface, and the positive and negative orders are positioned on opposite sides of the line406. Although not shown here, additional diffraction beams may also be produced, such as when m equals ±3, ±4, and ±5.

The diffraction angle θdof each beam404a-404dinFIG.4can be expressed as follows:
sin θd=sin θi+mλ/Λ(1)
As seen in Equation (1), the diffraction angle of each beam404a-404dis based on the incident angle θiof the optical beam402(meaning the direction or angle of arrival of the beam402at the diffraction grating214), the order m of the diffraction beam, the wavelength Λ of the optical beam402, and the period Λ of the diffraction grating214. This shows that the direction or angle of arrival and the wavelength of each of the input beams204a-204dat the diffraction grating214can be selected in order to help ensure that the diffractions of the input beams204a-204dfrom the diffraction grating214occur at the same diffraction angle θd, thereby combining portions of the input beams204a-204dto produce the HEL beam106. For instance, the directions or angles of arrival and the wavelengths of the input beams204a-204dcan be selected so that their first-order diffractions all have the same diffraction angle θd.

This also shows that, in some embodiments, an input beam used in place of the auto-alignment beam208(meaning an input beam having the same angle of arrival) may have a wavelength of λ, while the auto-alignment beam208may have a wavelength of 0.5λ. Here, the first-order diffraction of the input beam and the second-order diffraction of the auto-alignment beam208would have an equal diffraction angle θd(since the order m for the input beam is 1 and its wavelength is λ, while the order m for the auto-alignment beam is 2 and its wavelength is 0.5λ). Thus, in these embodiments, the auto-alignment beam208can have one-half the wavelength of an input laser beam at the same angle of arrival. In other embodiments, Equation (1) can be used to select other wavelengths and angles of arrival for the input laser beams204a-204dand the auto-alignment beam208to ensure that diffractions of the beams204a-204d,208have the same diffraction angle θd.

AlthoughFIG.3illustrates one example of a diffraction grating214andFIG.4illustrates one example of the operation of the diffraction grating214in a spectral beam combiner supporting an embedded auto-alignment scheme, various changes may be made toFIGS.3and4. For example, other diffraction gratings214may be used in the laser system102in place of the diffraction grating214shown inFIG.3. Also, the diffractions shown inFIG.4are examples only and can vary based on a number of factors, such as the incident angle θiand wavelength of the beam402and the design of the diffraction grating214.

FIG.5illustrates an example method500for using an embedded auto-alignment scheme in a spectral beam combiner according to this disclosure. For ease of explanation, the method500shown inFIG.5may be described as involving the use of the laser system102ofFIG.2in the system100ofFIG.1to engage a hostile target104. However, the method500ofFIG.5may be used with any other suitable laser system designed in accordance with this disclosure that operates within any other suitable environment and for any other suitable purpose.

As shown inFIG.5, multiple input beams and an auto-alignment beam are generated at step502. This may include, for example, multiple input lasers202a-202dproducing multiple input laser beams204a-204dand an auto-alignment laser206producing an auto-alignment laser beam208. This may also include the lasers202a-202d,206providing the beams204a-204d,208to a fiber launcher210. The input beams and the auto-alignment beam are reflected or otherwise processed using a transform optic at step504, and the beams are received at a diffraction grating at step506. This may include, for example, the fiber launcher210launching the beams204a-204d,208towards a transform optic212. This may also include the transform optic212focusing or otherwise processing the beams204a-204d,208so that the beams204a-204d,208are focused and directed at appropriate angles onto a diffraction grating214.

The input beams are combined using the diffraction grating to produce a combined beam at step508. This may include, for example, the diffraction grating214diffracting each of the input beams204a-204d, where first-order diffractions of the beams204a-204ddiffract from the grating214at the same angle θd. As shown in Equation (1) above, this can be accomplished by appropriate selection of the angles of arrival of the input beams204a-204dat the diffraction grating214and/or the wavelengths of the input beams204a-204d. Since the first-order diffractions of the beams204a-204ddiffract from the grating214at the same angle θd, this results in the generation of a combined beam, such as an HEL beam106, having a higher power or energy relative to the individual input beams204a-204d. One or more other portions of the input beams204a-204dmay be terminated using one or more beam dumps216.

A second-order diffraction or other diffraction of the auto-alignment beam that is co-boresighted to the combined beam is provided from the diffraction grating at step510. This may include, for example, the diffraction grating214diffracting the auto-alignment beam208so that a second-order diffraction or other higher-order diffraction of the auto-alignment beam208diffracts from the grating214at the same angle θdas the input beams202a-202d. As shown in Equation (1) above, this can be accomplished by appropriate selection of the angle of arrival of the auto-alignment beam208at the diffraction grating214and/or the wavelength of the auto-alignment beam208. This results in the generation of an auto-alignment beam208athat co-propagates with the HEL beam106or other combined beam. One or more other portions of the auto-alignment beam208(such as the auto-alignment beam208b) may be terminated using one or more beam dumps216.

The combined beam and the co-propagating auto-alignment beam are transported through a laser system at step512. This may include, for example, various mirrors218,220,222,224and a beam splitter226being used to redirect the HEL beam106or other combined beam and the co-propagating auto-alignment beam208aas needed.

Most or all of the combined beam is output at step514. This may include, for example, the beam splitter226providing the bulk or all of the HEL beam106through an exit aperture228. The auto-alignment beam is used to control the laser system at step516. This may include, for example, the beam splitter226providing at least part of the auto-alignment beam208a(and possibly part of the HEL beam106or other combined beam) to at least one sensor230. This may also include the sensor230sensing the location of the auto-alignment beam208a, such as an absolute location or its location relative to the HEL beam106or other combined beam. This may further include the controller232controlling a fast steering mirror224or other optical device(s) to adjust the position of the auto-alignment beam208a, which also adjusts the position of the HEL beam106or other combined beam.

AlthoughFIG.5illustrates one example of a method500for using an embedded auto-alignment scheme in a spectral beam combiner, various changes may be made toFIG.5. For example, while shown as a series of steps, various steps inFIG.5can overlap, occur in parallel, occur in a different order, or occur any number of times. Also, the use of optical devices such as transform optics, mirrors, beam combiners, and beam splitters can vary widely depending on the implementation.

In some embodiments, various functions described in this patent document are implemented or supported by a computer program that is formed from computer readable program code and that is embodied in a computer readable medium. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. A “non-transitory” computer readable medium excludes wired, wireless, optical, or other communication links that transport transitory electrical or other signals. A non-transitory computer readable medium includes media where data can be permanently stored and media where data can be stored and later overwritten, such as a rewritable optical disc or an erasable storage device.

It may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The terms “application” and “program” refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or a portion thereof adapted for implementation in a suitable computer code (including source code, object code, or executable code). The term “communicate,” as well as derivatives thereof, encompasses both direct and indirect communication. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrase “associated with,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like. The phrase “at least one of,” when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one item in the list may be needed. For example, “at least one of: A, B, and C” includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C.

The description in the present application should not be read as implying that any particular element, step, or function is an essential or critical element that must be included in the claim scope. The scope of patented subject matter is defined only by the allowed claims. Moreover, none of the claims invokes 35 U.S.C. § 110(f) with respect to any of the appended claims or claim elements unless the exact words “means for” or “step for” are explicitly used in the particular claim, followed by a participle phrase identifying a function. Use of terms such as (but not limited to) “mechanism,” “module,” “device,” “unit,” “component,” “element,” “member,” “apparatus,” “machine,” “system,” “processor,” or “controller” within a claim is understood and intended to refer to structures known to those skilled in the relevant art, as further modified or enhanced by the features of the claims themselves, and is not intended to invoke 35 U.S.C. § 110(f).

While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure, as defined by the following claims.