Patent Description:
The disclosure is related to gain medium amplifiers and passively Q-switched lasers and methods for operation and manufacture thereof, and especially to passively Q-switched lasers which include ceramic crystalline materials.

Lasers operating in the short-wave infrared (SWIR) part of the electromagnetic spectrum can be hard to manufacture in high volumes, especially if low production costs are required. There is therefore a need in the art for passively Q-switched SWIR lasers which can be produced in low costs and in large numbers.

Further limitations and disadvantages of conventional, traditional, and proposed approaches will become apparent to one of skill in the art, through comparison of such approaches with the subject matter of the present application as set forth in the remainder of the present application with reference to the drawings.

In order to understand the disclosure and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings.

discloses an optically pumped flat neodymium-doped yttrium aluminum garnet (Nd:YAG) gain medium amplifier crystal having a first end surface, through which incoming laser light enters the flat Nd:YAG crystal, and a second end surface opposite the first end surface through which outgoing laser light is emitted after being internally reflected in a zigzag manner between opposite first and second sides surfaces of the flat Nd:YAG crystal.

<CIT> discloses an optically pumped flat neodymium-doped yttrium aluminum garnet (Nd:YAG) gain medium amplifier crystal having a first end surface, through which incoming laser light enters the flat Nd:YAG crystal, and a second end surface opposite the first end surface through which outgoing laser light is emitted after being internally reflected in a zigzag manner between the first and second end surfaces.

<NPL>, discloses an optically pumped Nd:YAG crystal gain medium amplifier emitting amplified light at <NUM>, wherein the laser diode pump light has a wavelength of <NUM>.

In various embodiments, there are additionally provided passively Q-switched lasers, suitable for providing laser light having the second frequency between <NUM>,<NUM> and <NUM>,<NUM> to the first side surface of the gain medium amplifier according to the invention as claimed, the passively Q-switched lasers comprising: a gain medium (GM) having a stimulated emission cross section σSE; a saturable absorber (SA) having an absorption cross section (σa) which is less than three times the σSE of the GM; and an optical resonator within which the GM and the SA are positioned, the optical resonator comprising a high reflectivity mirror and an output coupler, wherein at least one of the high reflectivity mirror and the output coupler comprises a curved mirror, directing light within the optical resonator such that an effective cross-section of a laser mode within the SA (ASA) is smaller than a cross-section of a laser mode within a Rayleigh length of the pump (AGM).

In some embodiments, the GM is made of neodymium-doped yttrium aluminum garnet (Nd:YAG) and the SA is made from cobalt-doped YAG (Co<NUM>+:YAG).

In some embodiments, the GM is made of neodymium-doped yttrium orthovanadate (YVO<NUM>), and the SA is made from three-valence vanadium-doped yttrium aluminum garnet (V<NUM>+:YAG).

In some embodiments, the GM is made of neodymium-doped yttrium orthovanadate (YVO<NUM>) and the SA is made from cobalt-doped YAG (Co<NUM>+:YAG).

In some embodiments, the high reflectivity mirror and the output coupler are rigidly coupled to the GM and the SA, such that the passively Q-switched laser is a monolithic microchip passively Q-switched laser.

In some embodiments, the high reflectivity mirror is a concave mirror.

In some embodiments, both of the high reflectivity mirror and the output coupler are concave mirrors. In some embodiments, the curvatures of the concave high reflectivity mirror and of the concave output coupler are such that the highest energy density is within the middle <NUM>% of the optical resonator.

In some embodiments, a diameter of the SA is smaller than a diameter of the GM, wherein the SA is surrounded by another material for releasing heat from the optical resonator.

In some embodiments, the passively Q-switched laser further includes at least one end-pumping light source and optics for focusing light of the diode pump light source into the optical resonator.

In some embodiments, the GM and the SA are polycrystalline materials.

In some embodiments, the passively Q-switched laser further includes undoped YAG in addition to the GM and to the SA, for preventing heat from accumulating in an absorptive region of the GM.

In some embodiments, the GM and the SA are implemented on a single piece of crystalline material doped with neodymium and with at least one other material.

In some embodiments, the passively Q-switched laser emits light through the output coupler within the wavelengths range of <NUM>,<NUM> and <NUM>,<NUM>, thus being suitable for providing laser light having the second frequency between <NUM>,<NUM> and <NUM>,<NUM> to the first side surface of the gain medium amplifier according to the invention as claimed.

In some embodiments, there is disclosed a SWIR electrooptical system, including the passively Q-switched laser according to any one of the previous paragraphs, and further including a SWIR photodetector array sensitive to the wavelength of the laser, for detecting reflections of laser illumination off at least one illuminated object.

In some embodiments, there is disclosed a SWIR electrooptical system, including the passively Q-switched laser according to any one of the previous paragraphs, and further including a time of flight (ToF) SWIR sensor sensitive to the wavelength of the laser, a controller operable to synchronize operation of the ToF SWIR sensor and the passively Q-switched laser, and a processor operable to process detections by the ToF SWIR sensor of reflections of laser illumination of the passively Q-switched laser, for determining a distance to at least one object in the field of view of the SWIR electrooptical system.

In order to understand the disclosure and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting examples only and in accordance with examples of the presently disclosed subject matter, with reference to the accompanying drawings, in which:.

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the disclosure. However, it will be understood by those skilled in the art that the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present disclosure.

Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as "processing", "calculating", "computing", "determining", "generating", "setting", "configuring", "selecting", "defining", or the like, include action and/or processes of a computer that manipulate and/or transform data into other data, said data represented as physical quantities, e.g. such as electronic quantities, and/or said data representing the physical objects.

The terms "computer", "processor", and "controller" should be expansively construed to cover any kind of electronic device with data processing capabilities, including, by way of non-limiting example, a personal computer, a server, a computing system, a communication device, a processor (e.g. digital signal processor (DSP), a microcontroller, a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), etc.), any other electronic computing device, and or any combination thereof.

The operations in accordance with the teachings herein may be performed by a computer specially constructed for the desired purposes or by a general-purpose computer specially configured for the desired purpose by a computer program stored in a computer readable storage medium.

As used herein, the phrase "for example," "such as", "for instance" and variants thereof describe non-limiting embodiments of the presently disclosed subject matter. Reference in the specification to "one case", "some cases", "other cases" or variants thereof means that a particular feature, structure, or characteristic described in connection with the embodiment(s) is included in at least one embodiment of the presently disclosed subject matter. Thus, the appearance of the phrase "one case", "some cases", "other cases" or variants thereof does not necessarily refer to the same embodiment(s).

It is appreciated that certain features of the presently disclosed subject matter, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the presently disclosed subject matter, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

In embodiments of the presently disclosed subject matter one or more stages illustrated in the figures may be executed in a different order and/or one or more groups of stages may be executed simultaneously and vice versa. The figures illustrate a general schematic of the system architecture in accordance with an embodiment of the presently disclosed subject matter. Each module in the figures can be made up of any combination of software, hardware and/or firmware that performs the functions as defined and explained herein. The modules in the figures may be centralized in one location or dispersed over more than one location.

<FIG> is a schematic functional block diagram illustrating an example of short-wave infrared (SWIR) optical system <NUM>, in accordance with examples of the presently disclosed subject matter. It is noted that there is no scientific consensus about the range of wavelengths which are considered part of the SWIR spectrum. Nevertheless, for the purposes of the present disclosure, the SWIR spectrum includes electromagnetic radiation in wavelengths which are longer than that of the visible spectrum, and which include at the very least the spectral range between <NUM>,<NUM> and <NUM>,<NUM>. The gain medium amplifier according to the present invention as claimed is configured to amplify incoming laser light having a frequency of between <NUM>,<NUM> and <NUM>,<NUM>. SWIR optical system <NUM> illustrated in <FIG> includes at least a passively Q-switched laser <NUM>, but may also include additional components such as corresponding sensor (for sensing light of the laser reflected from external objects), processor (for processing sensing results), controller (for controlling activity of the laser, e.g., for synching its operation with that of the laser), and so on. Some such examples are discussed in further details below (e.g., with respect to <FIG>, and <FIG>).

The only industry that has required high volumes of lasers in the aforementioned spectral range (<NUM>-<NUM>) is the electronics industry for optical data storage, which drove the diode laser cost down to dollars, or less, per device, per Watt. However, those lasers are not suitable for other industries such as the automotive industry, which requires lasers with considerably greater peak power and beam brightness, and which will be utilized in harsh environmental conditions.

Passively Q-switched laser <NUM> includes at least a crystalline GM <NUM>, a crystalline SA <NUM>, and an optical cavity <NUM> in which the aforementioned crystalline materials are confined, in order to allow light propagating within the GM to intensify towards producing a laser light beam. Optical cavity <NUM> is also known by the terms "optical resonator" and "resonating cavity", and it includes a high reflectivity mirror <NUM> (also referred to as "high reflector") and an output coupler <NUM>. Discussed below are several unique and novel combinations of crystalline materials of different types, and using varied manufacturing techniques of the lasers, which allow for high volume manufacturing of reasonably priced lasers for the SWIR spectral range. General details which are generally known in the art with respect to passively Q-switched lasers are not provided here for reasons of conciseness of the disclosure, but are readily available for wide variety of sources. The SA of the laser serves as the Q-switch for the laser, as is known in the art. The term "crystalline material" broadly includes any material which is in either monocrystalline form or polycrystalline form.

The dimensions of the connected crystalline GM <NUM> and crystalline SA <NUM> may depend on the purpose for which a specific passively Q-switched laser <NUM> is designed. In a non-limiting example, a length of aforementioned combination is between <NUM> and <NUM> millimeters. In a non-limiting example, a length of aforementioned combination is between <NUM> and <NUM> millimeters. In a non-limiting example, a diameter of aforementioned combination (e.g., if a round cylinder) is between <NUM> and <NUM> millimeters. In a non-limiting example, a diameter of aforementioned combination (e.g., if a round cylinder) is between <NUM> and <NUM> millimeters.

The passively Q-switched laser <NUM> includes a GM crystalline material (GMC) which is rigidly connected to a SA crystalline material (SAC). The rigid coupling may be implemented in any one of the ways known in the art such as using adhesive, diffusion bonding, composite crystal bonding, growing one on top of the other, and so on. However, as discussed below, rigidly connecting crystalline materials which are in a ceramic form may be achieved using simple and cheap means. It is noted that the GM crystalline material and the SA crystalline material may be rigidly connected directly to one another, but may optionally be rigidly connected to one another via an intermediate object (e.g., another crystal). In some implementation, both the GM and the SA may be implemented on single piece of crystalline material, by doping different parts of the single piece of crystalline material with different dopants (such as the ones discussed below with respect to SA crystalline materials and to GM crystalline materials), or by co-doping a single piece of crystalline material, doping the same volume of the crystalline material with the two dopants (e.g., a ceramic YAG co-doped with N<NUM>+ and V<NUM>+). Optionally, GM may be grown on a single crystal saturable absorbing substrate (e.g., using Liquid Phase Epitaxy, LPE). It is noted that separate GM crystalline material and SA crystalline material are discussed extensively in the disclosure below, a single piece of ceramic crystalline material doped with two dopants may also be used in any of the following implementations, mutatis mutandis.

<FIG> are schematic functional block diagrams illustrating examples of passively Q-switched laser <NUM>, in accordance with examples of the presently disclosed subject matter. In <FIG> the two dopants are implemented on two parts of the common crystalline material <NUM> (acting both as GM and SA), while in <FIG> the two dopants are implemented interchangeably on common volume of the common crystalline material <NUM> (in the illustrated case - the entirety of the common crystal). Optionally, the GM and the SA may be implemented on a single piece of crystalline material doped with neodymium and at least one other material. Optionally (e.g., as exemplified in <FIG>), any one or both of the optical coupler <NUM> and the high reflectivity mirror <NUM> may be glued directly to one of the crystalline materials (e.g., the GM or the SA, or a crystal combining both).

At least one of the SA crystalline material and the GM crystalline material is a ceramic crystalline material, i.e., the relevant crystalline material (e.g., doped yttrium aluminum garnet, YAG, doped vanadium) in a ceramic form (e.g., a polycrystalline form). Having one-and especially both-crystalline material in ceramic form allows for production in higher numbers and in lower costs. For example, instead of growing separate monocrystalline materials in a slow and limited process, polycrystalline materials may be manufactured by sintering of powders (i.e., compacting and possibly heating a powder to form a solid mass), low temperature sintering, vacuum sintering, and so on. One of the crystalline materials (SA crystalline material or GM crystalline material) may be sintered on top of the other, obviating the need for complex and costly processes such as polishing, diffusion bonding, or surface activated bonding. Optionally, at least one of the GM crystalline material and the SA crystalline material is polycrystalline. Optionally, both the GM crystalline material and the SA crystalline material is polycrystalline.

Referring to the combinations of crystalline materials from which the GM crystalline material and the SA crystalline material may be made, such combinations may include:.

It is noted that in any one of the implementations, a doped crystalline material may be doped with more than one dopant. For example, the SA crystalline material may be doped with the main dopant disclosed above, and with at least one other doping material (e.g., in significantly lower quantities). A neodymium-doped rare-earth element crystalline material is a crystalline material whose unit cell comprises a rare-earth element (one of a well-defined group of <NUM> chemical elements, including the fifteen lanthanide elements, as well as scandium and yttrium) and which is doped with neodymium (e.g., triply ionized neodymium) which replaces the rear-earth element in a fraction of the unit cells. Few non-limiting examples of neodymium-doped rare-earth element crystalline material which may be used in the disclosure are:.

The following discussion applies to any of the optional combinations of GM crystalline materials and SA crystalline materials.

Optionally, the GM crystalline material is rigidly connected directly to the SA crystalline material. Alternatively, the GM crystalline material and the SA crystalline material may be connected indirectly (e.g., each of the SA crystalline material and GM crystalline material being connected via a group of one or more intermediate crystalline materials and/or via one or more other solid materials transparent to the relevant wavelengths). Optionally one or both of the SA crystalline material and the GM crystalline material are transparent to the relevant wavelengths.

Optionally, the SA crystalline material may be cobalt-doped Spinel (Co Co<NUM>+:MgAl2O4). Optionally, the SA crystalline material may be cobalt-doped YAG (Co:YAG). Optionally, this may enable co-doping of cobalt and neodymium Nd on the same YAG. Optionally, the SA crystalline material may be cobalt-doped Zinc selenide (Co<NUM>+:ZnSe). Optionally, the GM crystalline material may be a ceramic cobalt-doped crystalline material.

Optionally, an initial transmission (To) of the SA is between <NUM>% and <NUM>%. Optionally, the initial transmission of the SA is between <NUM>% and <NUM>%.

The wavelengths emitted by the laser depend on the material used in its construction, and especially on the materials and dopants of the GM crystalline material and the SA crystalline material. Some examples of output wavelengths include wavelengths in the range of <NUM>,<NUM> and <NUM>,<NUM>. Some more specific examples include <NUM> or about <NUM> (e.g., <NUM>±<NUM>), <NUM> or about <NUM> (e.g., <NUM>±<NUM>), <NUM> or about <NUM> (e.g., <NUM>±<NUM>). A corresponding imager sensitive to one or more of these light frequency ranges may be included in SWIR optical system <NUM> (e.g., as exemplified in <FIG>). The gain medium amplifier according to the present invention as claimed is configured to amplify incoming laser light having a frequency of between <NUM>,<NUM> and <NUM>,<NUM>.

<FIG> are schematic functional diagrams illustrating SWIR optical system <NUM>, in accordance with examples of the presently disclosed subject matter. As exemplified in these illustrations, laser <NUM> may include additional components in addition to those discussed above, such as (but not limited to):.

Optionally, SWIR optical system <NUM> may include optics to spread the laser over a wider field of view (FOV), in order to improve eye safety issues in the FOV. Optionally the passively Q-switched laser <NUM> is a diode pumped solid state laser (DPSSL).

Optionally, passively Q-switched laser <NUM> includes at least one diode pump light source <NUM> and optics <NUM> for focusing light of the pump light source <NUM> into the optical resonator. Optionally, light source <NUM> is positioned on the optical axis (as an end pump). Optionally, light source <NUM> may be rigidly connected to high reflectivity mirror <NUM> or to the SA <NUM>, such that light source <NUM> is a part of a monolithic microchip passively Q-switched laser. Optionally, the light source of the laser may include one or more vertical-cavity surface-emitting laser (VCSEL) array. Optionally, passively Q-switched laser <NUM> includes at least one VCSEL array and optics for focusing light of the VCSEL array into the optical resonator. The wavelengths emitted by the light source (e.g., the laser pump) may depend on the crystalline materials and/or dopants used in the laser. Some example pumping wavelengths which may be emitted by the pump include: <NUM> or about <NUM>, <NUM> or about <NUM>, about nine hundred and some nm.

<FIG> is a schematic functional block diagram illustrating a SWIR optical system <NUM>, in accordance with other examples of the presently disclosed subject matter. As mentioned above, SWIR optical system <NUM> may include additional components such as any one or more of the following components: corresponding sensor <NUM> (for sensing light of the laser reflected from external objects), processor <NUM> (for processing sensing results), controller <NUM> (for controlling activity of the laser, e.g., for synching its operation with that of the laser), and so on. Some such examples are discussed in further details below. Optionally, SWIR optical system <NUM> may include SWIR photodetector array <NUM> sensitive to the wavelength of the laser. This way SWIR optical system may serve as an active SWIR camera, SWIR time-of-flight (ToF) sensor, SWIR light detection and ranging (LIDAR) sensor, and so on. Optionally, SWIR optical system <NUM> may include a ToF SWIR sensor sensitive to the wavelength of the laser. Optionally, the photodetector array may be a CMOS based photodetector array which is sensitive to SWIR frequencies emitted by laser <NUM>, such is a CMOS based photodetector arrays designed and manufactured by TriEye LTD. Of Tel Aviv, Israel.

Optionally, SWIR optical system <NUM> may include processor <NUM> for processing detection data from SWIR photodetector array <NUM> (or any other light sensitive sensor of SWIR optical system <NUM>). For example, processor <NUM> may process the detection information to provide a SWIR image of a field-of-view (FOV) of SWIR optical system <NUM>, in order to detect objects in the FOV, and so on. Optionally, SWIR optical system <NUM> may include a time of flight (ToF) SWIR sensor (e.g., as sensor <NUM>) sensitive to the wavelength of the laser, and a controller operable to synchronize operation of the ToF SWIR sensor and the passively Q-switched SWIR laser for detecting a distance to at least one object <NUM> in the field of view of SWIR optical system <NUM>. Optionally, SWIR optical system <NUM> may include a controller <NUM> operable to control one or more aspects of an operation of Q-switched laser <NUM> or other components of the system such as the photodetector array <NUM> (e.g., focal plane array, FPA). For example, some of the parameters of the laser which may be controlled by controller <NUM> include timing, duration, intensity, focusing, and so on. While not necessarily so, controller <NUM> may control operation of laser <NUM> based on detection results of the photodetector array (directly, or based on processing by processor <NUM>). Optionally, controller <NUM> may be operable to control the laser pump or other type of light source in order to affect activation parameters of laser <NUM>. Optionally, controller <NUM> may be operable to dynamically change the pulse repetition rate. Optionally, controller <NUM> may be operable to control dynamic modification of the light shaping optics, e.g., for improving a Signal to Noise Ratio (SNR) in specific regions of the field of view. Optionally, controller <NUM> may be operable to control the illumination module for dynamically changing pulse energy and/or duration, (e.g., in the same ways possible for other passively Q-switched lasers, such as changing focusing of pumping laser, etc.).

Optionally, SWIR optical system <NUM> may include temperature control (e.g., passive temperature control, active temperature control) for controlling a temperature of the laser generally, or of one or more of its components (e.g., of the pump diode). Such temperature control may include, for example, a thermoelectric cooler (TEC), a fan, a heat sink, resistance heater under pump diode, and so forth.

The power of the laser may depend on the utilization for which it is designed. For example, the laser output power may be between 1W and 5W. For example, the laser output power may be between 5W and 15W. For example, the laser output power may be between 15W and 50W. For example, the laser output power may be between 50W and 200W. For example, the laser output power may be higher than 200W.

<FIG> is a schematic functional block diagram illustrating yet another SWIR optical system <NUM>, in accordance with yet other examples of the presently disclosed subject matter. As exemplified in <FIG>, system <NUM> may include a laser amplifier <NUM>, for amplifying the output light signal of laser <NUM>. The amplifier <NUM> may be pumped by a dedicated diode <NUM>, or using any other suitable light source. It is noted that laser amplifier <NUM> may be implemented as an independent amplification unit <NUM> (illustrated), as part of laser <NUM> (e.g., rigidly connected to laser <NUM>), or as part of any other system. It is noted that laser amplifier <NUM> may also be implemented in other configurations of electrooptic system <NUM> (e.g., ones that use side pumping), even if not illustrated.

The SWIR-Q-switched laser <NUM> is a pulsed laser, and may have different frequency (repetition rate), different pulse energy, and different pulse duration, which may depend on the utilization for which it is designed. For example, a repetition rate of the laser may be between <NUM> and <NUM>. For example, a repetition rate of the laser may be between <NUM> and <NUM>. For example, a pulse energy of the laser may be between <NUM>. 1mJ and 1mJ. For example, a pulse energy of the laser may be between 1mJ and 2mJ. For example, a pulse energy of the laser may be between 2mJ and 5mJ. For example, a pulse energy of the laser may be higher than 5mJ. For example, a pulse duration of the laser may be between 10ns and 100ns. For example, a pulse duration of the laser may be between <NUM> and <NUM>. For example, a pulse duration of the laser may be between <NUM> and <NUM>. The Size of the laser may also change, depending for example on the size of its components. For example, the laser dimensions may be X<NUM> by X<NUM> by X<NUM>, wherein each of the dimensions (X<NUM>,X<NUM>, and X<NUM>) is between <NUM> and <NUM>, between <NUM> and <NUM>, and so on. The output coupling mirror may be flat, curved, or slightly curved.

Optionally, SWIR optical system <NUM> may further include undoped YAG in addition to the GM and to the SA, for preventing heat from accumulating in an absorptive region of the GM. The undoped YAG may optionally be shaped as a cylinder (e.g., a concentric cylinder) encircling the GM and the SA.

It is noted that SWIR optical system <NUM> may include additional components, in addition to the ones discussed above. Few nonlimiting examples are provided below. Optionally, SWIR optical system <NUM> may include another laser which is used to bleach at least one of the GM and the SA. Optionally, SWIR optical system may include an internal photosensitive detector (e.g., one or more photodiodes) which are operable to measure a time in which a pulse is generated by Passively Q-switched laser <NUM>, wherein the processor is operable to issue, based on the timing information obtained from the internal photosensitive detector, a triggering signal to the photodetector array (or other type of camera or sensor) which detects reflection of laser light from objects in the field of view of system <NUM>. Such an internal photosensitive detector is exemplified in <FIG> (denoted as "Pulse detection photodiode" in the illustrated example).

<FIG> is a flow chart illustrating an example of method <NUM>, in accordance with examples of the presently disclosed subject matter. Method <NUM> is a method for manufacturing parts for a passively Q-switched laser such as but not limited to passively Q-switched laser <NUM> discussed above. Referring to the examples set forth with respect to the previous drawings, the passively Q-switched laser may be laser <NUM>. It is noted that any variation discussed with respect to laser <NUM> or to a component thereof may also be implemented for the passively Q-switched laser whose parts are manufactured in method <NUM> or to a corresponding component thereof, and vice versa.

Method <NUM> starts with stage <NUM> of inserting into a first mold at least one first powder, which is processed later in method <NUM> to yield a first crystalline material. The first crystalline material serves as either the GM or the SA of the passively Q-switched laser. In some implementations the GM of the laser is made first (e.g., by way of sintering), and the SA is made later on top of the previously made GM (e.g., by way of sintering). On other implementations, the SA of the laser is made first, and the GM is made later on top of the previously made SA. In yet other implementations, the SA and the GM are made independently of one another, and are coupled to form a single rigid body. The coupling may be done as part of the heating, sintering, or later.

Stage <NUM> of method <NUM> includes inserting into a second mold at least one second powder different than the at least one first powder. The at least one second powder is processed later in method <NUM> to yield a second crystalline material. The second crystalline material serves as either the GM or the SA of the passively Q-switched laser (so that one of the SA and the GM is made from the first crystalline material and the other functionality is made from the second crystalline material).

The second mold may be different from the first mold. Alternatively, the second mold may be the same as the first mold. In such case the at least one second powder may be inserted, for example, on top of the at least one first powder (or on top of the first green body, if already made), beside it, around it, and so on. The inserting of the at least one second powder into the same mold of the at least one first powder (if implemented) may be executed before processing of the at least one first powder into a first green body, after processing of the at least one first powder into the first green body, or sometime during the processing of the at least one first powder into the first green body.

The first powder and/or the second powder may include crushed YAG (or any of the other aforementioned materials such as Spinel, MgAl<NUM>O<NUM>, ZnSe) and doping materials (e.g., N<NUM>+, V<NUM>+, Co). The first powder and/or the second powder may include materials from which YAG (or any of the other aforementioned materials such as Spinel, MgAl<NUM>O<NUM>, ZnSe) is made and doping material (e.g., N<NUM>+, V<NUM>+, Co).

Stage <NUM> is executed after stage <NUM>, and includes compacting the at least one first powder in the first mold to yield a first green body. Stage <NUM> is executed after stage <NUM>, and includes compacting the at least one second powder in the second mold, thereby yielding a second green body. If the at least one first powder and the at least one second powder are inserted into the same mold in stages <NUM> and <NUM>, the compacting of the powders in stage <NUM> and <NUM> may be done concurrently (e.g., pressing on the at least one second powder, which in turn compresses the at least one first powder against the mold), but this is not necessarily so. For example, stage <NUM> (and therefore also stage <NUM>) may optionally be executed after the compressing of stage <NUM>.

Stage <NUM> includes heating the first green body to yield a first crystalline material. Stage <NUM> includes heating the second green body to yield a second crystalline material. in different embodiments, the heating of the first crystalline may be executed before, concurrently, partly concurrently, or after each one of stages <NUM> and <NUM>.

Optionally, the heating of the first green body at stage <NUM> precedes the compacting (and possibly also precedes the inserting) of the at least one second powder in stage <NUM> (and possibly stage <NUM>). The first green body and the second green body may be heated separately (e.g., in different times, in different temperatures, for different durations). The first green body and the second green body may be heated together (e.g., in the same oven), either connected to each other during the heating or not. The first green body and the second green body may be subject to different heating regimes, which may share partial co-heating, while being heated separately in other parts of the heating regimes. For example, one or both of the first green body and the second green body may be heated separately from the other green body, and then the two green bodies may be heated together (e.g., after coupling, but not necessarily so). Optionally, the heating of first green body and the heating of the second green body comprise concurrent heating of the first green body and the second green body in a single oven. It is noted that optionally, the coupling of stage <NUM> is a result of the concurrent heating of both of the green bodies in the single oven. It is noted that optionally, the coupling of stage <NUM> is done by co-sintering both of the green bodies after being physically connected to one another.

Stage <NUM> of method <NUM> includes coupling the second crystalline material to the first crystalline material. The coupling may be executed in any way of coupling known in the art, several nonlimiting examples of which were discussed above with respect to passively Q-switched laser <NUM>. It is noted that the coupling may have several sub-stages, some of which may intertwine with different stages out of stages <NUM>, <NUM>, <NUM>, and <NUM> in different manners in different embodiments. The coupling results in a single rigid crystalline body which includes both the GM and the SA.

It is noted that method <NUM> may include additional stages which are used in the making of crystals (and especially in the making of ceramic or non-ceramic polycrystalline crystal compounds of polycrystalline materials which are bounded to each other). Few nonlimiting examples include powder preparation, binder burn-out, densification, annealing, polishing (if required, as discussed below), and so on.

The GM of the passively Q-switched laser in method <NUM> (which, as aforementioned, can be either the first crystalline material or the second crystalline material), is a neodymium-doped crystalline material. The SA of the passively Q-switched laser in method <NUM> (which, as aforementioned, can be either the first crystalline material or the second crystalline material), is selected from a group of crystalline materials consisting of: (a) a neodymium-doped crystalline material, and (b) a doped crystalline material selected from a group of doped crystalline materials consisting of: three-valence vanadium-doped yttrium aluminum garnet (V<NUM>+:YAG) and cobalt-doped crystalline materials. At least one of the GM and the SA is a ceramic crystalline material. Optionally, both of the GM and the SA are ceramic crystalline materials. Optionally, at least one of the GM and the SA is a polycrystalline material. optionally, both the GM and the SA are polycrystalline materials.

While additional stages of the manufacturing process may take place between the different stages of method <NUM>, notably polishing of the first material before bonding of the second material in the process of sintering is not required in at least some of the implementations.

Referring to the combinations of crystalline materials from which the GM crystalline material and the SA crystalline material may be made in method <NUM>, such combinations may include:.

Referring to method <NUM> as a whole, it is noted that optionally one or both of the SA crystalline material and the GM crystalline material (and optionally one or more intermediate connecting crystalline materials, if any) are transparent to the relevant wavelengths (e.g., SWIR radiation).

<FIG> and <FIG> include several conceptual timelines for the execution of method <NUM>, in accordance with examples of the presently disclosed subject matter. In order to simplify the drawing, it is assumed that the SA is a result of the processing of the at least one first powder, and that the GM is a result of the processing of the at least one second powder. As mentioned above, the roles may be reversed.

<FIG> are schematic functional block diagrams illustrating examples of a passively Q-switched lasers <NUM>, in accordance with examples of the presently disclosed subject matter. Optionally, laser <NUM> may be implemented as any suitable variation of laser <NUM> discussed above, but this is not necessarily so. Laser <NUM> may be a part of an electrooptical system <NUM>. Optionally, electrooptical system <NUM> may be implemented as any suitable variation of electrooptical system <NUM> discussed above, but this is not necessarily so.

Laser <NUM> includes GM <NUM> that is characterized by a stimulated emission cross section denoted (denoted σSE). Laser <NUM> also includes SA <NUM> that is characterized by an absorption cross section (denoted σa). In some combinations of materials of GM <NUM> and SA <NUM>, σa is smaller than σSE, or not significantly larger from the σSE (e.g., σa < <NUM>·σSE). For example, GM <NUM> may be made from neodymium-doped yttrium aluminum garnet (Nd:YAG), and SA <NUM> may be made from cobalt-doped YAG (Co<NUM>+:YAG). In such cases, most of the pump energy stored in GM <NUM> is used for saturating SA <NUM>, leaving only a small fraction of the energy for amplification. In order to reduce the amount of energy required to saturate the absorber, laser <NUM> includes an optical resonator with dedicated geometry, as discussed in greater detail below. In the proposed geometries, only a small fraction of the stored energy is required to saturate the absorber, leading to high efficiency and therefore high output energy.

The optical resonator (within which GM <NUM> and SA <NUM> are positioned) includes high reflectivity mirror <NUM> and output coupler <NUM>. At least one of HR mirror <NUM> and OC <NUM> includes a curved mirror, such that the combinations of mirrors of the optical resonator directs light within the optical resonator which causes an effective cross-section of the laser mode within the SA (denoted ASA) to be smaller than a cross-section of the laser mode within a Rayleigh length of the pump beam (denoted AGM). It is noted that while a diameter of the mode may change somewhat within the SA, it would not change by much, since SA <NUM> is relatively narrow. Therefore, for simplicity of calculations, a single effective diameter may represent the small range of diameters of the mode within the SA (the effective diameter being included in the small range of diameters, and usually close to an average diameter of the mode along SA <NUM>).

The laser mode is denoted <NUM> in the diagram, and the pumped volume is denoted <NUM>. A waist of the pumped volume is denoted <NUM>. In cases in which the cross-section of the laser mode within the SA in not constant along the entire SA <NUM>, ASA may represent an average effective cross-section of the laser mode throughout SA <NUM>. Likewise, in cases in which the cross-section of the laser mode is not constant throughout the Rayleigh length of the pump, AGM may represent an average cross-section of the laser mode within the Rayleigh length of the pump. The Rayleigh length (or Rayleigh range) of a laser beam is the distance from the beam waist (in the propagation direction) where the beam radius is increased by a factor of the square root of <NUM> (e.g., for a circular beam, the mode area is doubled at this point). It is noted that both ASA and AGM are geometrical area (e.g., measured in cm<NUM> units), while σa and σSE are properties of the materials of GM <NUM> and of SA <NUM>, and are also represented in area units (e.g., in cm<NUM> units).

Using concave mirrors focuses larger energy density per area unit in SA <NUM> with respect to the energy density per area unit in GM <NUM>, which causes only a small fraction of the stored energy is required to saturate the absorber, leading to high efficiency and therefore high output energy.

The focusing of energy may be done to different degrees, depending on various considerations such as materials chosen for the GM and the SA, desired laser output power, and so on. For example, the radius of the one or more concave mirrors (out of HR mirror <NUM> and OC <NUM>) may be selected such that a ratio between σSE and AGM is smaller by a factor of at least three than a ratio between σa and ASA <MAT>. Other ratios may also be chosen. For example, the geometry of the optical resonator may be such that: <MAT> ; <MAT>or <MAT>.

As mentioned above, optionally GM <NUM> may be made of neodymium-doped yttrium aluminum garnet (Nd:YAG) and SA <NUM> may be made from cobalt-doped YAG (Co<NUM>+:YAG). However, other materials may be used for either GM <NUM> or SA <NUM>. In a nonlimiting example, any of the materials discussed above with respect to the GM and the SA of passively Q-switched laser <NUM> may be used for GM <NUM> and for SA <NUM>, respectively. GM <NUM> and SA <NUM> may be implemented on the same type of crystal (e.g., YAG, Spinel, Zinc selenide) with different dopants, but this is not necessarily so.

As mentioned above, optionally passively Q-switched laser <NUM> may be a microchip laser, e.g., as discussed above with respect to passively Q-switched laser <NUM> (mutatis mutandis). Optionally, high reflectivity mirror <NUM> and output coupler <NUM> are rigidly coupled to GM <NUM> and to SA <NUM>, such that the passively Q-switched laser is a monolithic microchip passively Q-switched laser. It is noted that those components are not necessarily coupled directly to one another. For example, undoped YAG (or any other suitable crystal) may be positioned between high reflectivity mirror <NUM> to GM <NUM>, between GM <NUM> and SA <NUM>, and/or between SA <NUM> and output coupler <NUM>. An example for such a configuration is provided in <FIG>, <FIG>.

Either one of HR mirror <NUM> and/or output coupler <NUM> may be a concave mirror (or an optical equivalent thereof). Such a concave mirror may be a spherical concave mirror or another type of concave mirror). Optionally, both of high reflectivity mirror <NUM> and output coupler <NUM> are concave mirrors (or optically equivalent arrangement). Such implementations are illustrated in <FIG>, in accordance with examples of the presently disclosed subject matter. Having both the HR mirror <NUM> and OC <NUM> curved may be used for different ends. For example, having both the HR mirror <NUM> and OC <NUM> curved may be used for shaping of the mode of the laser. For example, having both the HR mirror <NUM> and OC <NUM> curved may be used for keeping the highest energy intensity distanced from optical surfaces such as mirror coatings (e.g., from the output coupler <NUM>), e.g., in order to prevent damaging of the OC by the heat generated in the SA <NUM>. Such a variation is illustrated in <FIG>. Optionally, the curvature of the concave HR mirror <NUM> and the curvature of the concave OC <NUM> are such than the highest energy density is within the middle <NUM>% of the optical resonator (i.e., if the distance between the furthest two points - one on the HR mirror and one on the OC - is denoted D, then the distance between HR mirror <NUM> and the location of highest energy density is larger than <NUM>. Also, in such case the distance between OC coupler and the location of highest energy density is larger than <NUM>.

Referring to the example of <FIG>, a diameter of SA <NUM> may optionally be smaller than a diameter of GM <NUM>, such that SA <NUM> is surrounded by another material (e.g., undoped YAG) for releasing heat from the optical resonator. It is noted that GM <NUM>, SA <NUM>, or both, may also be covered in undoped YAG (or another type of crystal or other material) to improve removal of heat from the laser <NUM> (even if a diameter of SA <NUM> is not smaller than that of GM <NUM>). In other words, optionally laser <NUM> may include undoped YAG (or other suitable material such any suitable crystal of the materials mentioned above) in addition to the GM and to the SA, for preventing heat from accumulating in an absorptive region of the GM. For example, the undoped YAG (or other suitable material) may be shaped as a cylinder encircling the GM and the SA.

It is noted that laser <NUM> may be an end pumped laser, or a side pump laser. <FIG> are schematic functional block diagrams illustrating examples of electrooptical system <NUM> with an end-pumped passively Q-switched laser <NUM> (<FIG>) and an electrooptical system <NUM> with a side-pumped passively Q-switched laser <NUM> (<FIG>), in accordance with examples of the presently disclosed subject matter. respectively. Optionally, laser <NUM> may include at least one end-pumping light source <NUM>, and optics <NUM> for focusing light of the diode pump light source into the optical resonator. Optionally, laser <NUM> may include at least one side-pumping light source <NUM>, and suitable optics <NUM> (e.g., a diffuser). An example for pumping light source includes (but are not limited to) a diode or a vertical-resonator surface-emitting laser (VCSEL) array. The components of <FIG> may be similar to the corresponding components of <FIG>, mutatis mutandis, and the components of <FIG> may be similar to the corresponding components of <FIG>, mutatis mutandis. The discussion is not repeated for reasons of brevity of the disclosure.

As mentioned above, any variation discussed with respect to laser <NUM> may also be applicable, mutatis mutandis, to laser <NUM>. For example, passively Q-switched laser <NUM> may include GM and SA that are polycrystalline materials. Optionally, GM <NUM> and SA <NUM> may be implemented on a single piece of crystalline material doped with neodymium and at least one other material. optionally, passively Q-switched laser <NUM> emits light through the output coupler within the wavelengths range of <NUM>,<NUM> and <NUM>,<NUM>. Optionally, Q-switched laser <NUM> may emit light through the output coupler within the wavelengths whose center frequency is selected from a group of center frequencies consisting of: (a) <NUM>±<NUM>, (b) <NUM>±<NUM>, and (c) <NUM>±<NUM>. Optionally, an initial transmission (To) of SA <NUM> is between <NUM>% and <NUM>%. Optionally, the initial transmission (To) of the SA <NUM> is between <NUM>% and <NUM>%. The gain medium amplifier according to the present invention as claimed is configured to amplify incoming laser light having a frequency of between <NUM>,<NUM> and <NUM>,<NUM>.

<FIG> are schematic functional block diagrams illustrating examples of electrooptical systems <NUM>, in accordance with examples of the presently disclosed subject matter. Referring to electrooptical system <NUM> as a hole, system <NUM> may include, in addition to laser <NUM>, also a SWIR photodetector array sensitive to the wavelength of the laser, for detecting reflections of laser illumination off at least one illuminated object. Optionally, system <NUM> may include a ToF SWIR sensor sensitive to the wavelength of the laser, a controller operable to synchronize operation of the ToF SWIR sensor and the passively Q-switched laser, and a processor operable to process detections by the ToF SWIR sensor of reflections of laser illumination of the passively Q-switched laser, for determining a distance to at least one object in the field of view of the SWIR electrooptical system.

<FIG> is a schematic functional block diagram illustrating an example of short-wave infrared (SWIR) optical system <NUM>, in accordance with examples of the presently disclosed subject matter. As exemplified in <FIG>, system <NUM> may include a laser amplifier <NUM>, for amplifying the output light signal of laser <NUM>. The amplifier <NUM> may be pumped by a dedicated diode <NUM>, or using any other suitable light source. It is noted that laser amplifier <NUM> may be implemented as an independent amplification unit <NUM> (illustrated), as part of laser <NUM> (e.g., rigidly connected to laser <NUM>), or as part of any other system. It is noted that laser amplifier <NUM> may also be implemented in other configurations of electrooptic system <NUM> (e.g., ones that use side pumping), even if not illustrated. The components of <FIG> may be similar to the corresponding components of <FIG>, mutatis mutandis, and the components of <FIG> may be similar to the corresponding components of <FIG>, mutatis mutandis. The discussion is not repeated for reasons of brevity of the disclosure.

It is noted that any variation discussed above of passively Q-switched laser <NUM> may be manufactured, for example, by implementing method <NUM> discussed above, mutatis mutandis. Method <NUM> may include the suitable stages required for giving the manufactured passively Q-switched laser the aforementioned characterizations of passively Q-switched laser <NUM> discussed above. For example, method <NUM> may be adapted to provide the manufactured passively Q-switched laser the physical characteristics discussed above (e.g., the stimulated emission cross section (σSE), the absorption cross section (σa), the effective cross-section of the laser mode within the SA).

<FIG> are exploded-view perspective projections of GM amplifiers <NUM>, in accordance with embodiments of the presently claimed invention. Referring to the examples set forth with respect to the previous drawings, it is noted that GM amplifier <NUM> may serve as laser amplifier <NUM> of system <NUM> (or of passively Q-switched laser <NUM>, if integrated in it). Referring to the examples set forth with respect to the previous drawings, it is noted that GM amplifier <NUM> may serve as laser amplifier <NUM> of system <NUM> (or of passively Q-switched laser <NUM>, if integrated in it). However, any suitable type of laser amplifiers may be implemented as laser amplifier <NUM> and/or <NUM>. GM amplifier <NUM> may be fed by any suitable seed laser (denoted <NUM>), such as-but not limited to-any variation of passively Q-switched laser <NUM> and passively Q-switched laser <NUM>.

GM amplifier <NUM> includes at least flat neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal <NUM>. Crystal <NUM> has an average thickness of less than <NUM> millimeters (e.g., about <NUM>, further examples are provided below), while at least one of the other dimensions of crystal <NUM> are longer (e.g., at least <NUM> times longer), and possibly both of the perpendicular dimensions are at least <NUM> times longer than the average thickness of crystal <NUM>.

Flat Nd:YAG crystal <NUM> includes at least:.

The flat Nd:YAG crystal may include additional side surfaces in addition to the surfaces mentioned above. Some or all of the surfaces of the flat Nd:YAG crystal (optionally including one or both of the first side surface and the second side surface) may be flat or substantially flat, but this is not necessarily so, and curved surfaces may also be implemented. The light is internally reflected within the flat Nd:YAG crystal from both of the first side surface and the second side surface. The light may additionally be internally reflected within the flat Nd:YAG crystal from one or more surfaces other than the first side surface and the second side surface, but this is not necessarily so. The first side surface and the second side surfaces may be parallel to each other, but this is not necessarily so. It is noted that the terms "top" and "bottom" are arbitrary terms used to identify to opposing sides, and these surfaces may be positioned in different orientations in different implementations of the disclosure. The top surface may be parallel to the bottom surface (e.g., as illustrated in the diagram), but this is not necessarily so. The first side surface may have at least one shared edge with the top surface and/or with the bottom surface, but this is not necessarily so. Additionally, the second side surface may have at least one shared edge with the top surface and/or with the bottom surface, but this is not necessarily so. It is noted that any combination of the above optional implementations may be implemented, even if not explicitly stated for reasons of brevity.

The number of times light is reflected internally within flat Nd:YAG crystal <NUM> before being emitted as outgoing laser light affects the gain of GM amplifier <NUM>, which is exponentially correlated to the distance light passes within the doped crystal. Optionally, the optical path of the incoming laser light until it is emitted as outgoing laser light includes at least <NUM> internal reflections <NUM>. Different number of internal reflections may also be implemented, such as between <NUM>-<NUM>, between <NUM>-<NUM>, between <NUM>-<NUM>, between <NUM>-<NUM>, or more. Optionally, the optical path of the incoming laser light until it is emitted as outgoing laser light is at least <NUM> times longer than the average thickness of the flat Nd:YAG crystal. Different ratios between the optical path and the average thickness may be implemented, such as between <NUM>-<NUM>, between <NUM>-<NUM>, or more than <NUM>.

The flat Nd:YAG crystal may be used to amplify specific frequencies. The pump light may be of one or more pump frequencies (or pump frequency ranges). In accordance with the invention as claimed, the pump frequency is between <NUM> nanometer (nm) and <NUM>. For example, the pump frequency may be between <NUM> and <NUM>. For example, the pump frequency may be between <NUM> and <NUM>. For example, the pump frequency may be between <NUM> and <NUM>. For example, the pump frequency may be <NUM>±<NUM>. However, other frequency ranges may be implemented. The pump light may be laser light (e.g., vertical-cavity surface-emitting laser or any other type of laser), light emitting diode (LED) light, or light of any other suitable source.

The outgoing laser light may be of one or more emitted light frequencies (or emitter frequency ranges). In accordance with the invention as claimed, the emitted light frequency is between <NUM>,<NUM> and <NUM>,<NUM>. For example, the emitted light frequency may be between <NUM>,<NUM> and <NUM>,<NUM>. For example, the emitted light frequency may be between <NUM>,<NUM> and <NUM>,<NUM>. For example, the emitted light frequency may be <NUM>,<NUM>±<NUM>.

The second laser frequency (also referred to as "incoming laser frequency") is the same frequency as the outgoing laser frequency. The second light frequency is between <NUM>,<NUM> and <NUM>,<NUM>. For example, the second light frequency may be between <NUM>,<NUM> and <NUM>,<NUM>. For example, the second light frequency may be between <NUM>,<NUM> and <NUM>,<NUM>. For example, the second light frequency may be <NUM>,<NUM>±<NUM>.

Top surface <NUM> has a longer first dimension (e.g., length) and a shorter second dimension (e.g., width) that is orthogonal to the first dimension. The first dimension is at least <NUM> times longer than the average thickness of the flat Nd:YAG crystal. For example, if the average thickness of the flat Nd:YAG crystal is <NUM>, the first dimension may be any length that is equal or larger to <NUM> (e.g., <NUM>, <NUM>, between <NUM>-<NUM>, between <NUM>-<NUM>, etc.). The average thickness may vary according to the application, such as smaller than <NUM>, between <NUM>-<NUM>, between <NUM>-<NUM>, between <NUM>-<NUM>, between <NUM>-<NUM>, and so on. The length of the flat Nd:YAG crystal is its largest measure along the first dimension. The average length along the first dimension is at least <NUM> times longer than the average thickness of the flat Nd:YAG crystal.

Optionally, flat Nd:YAG crystal <NUM> is a prism. Optionally, flat Nd:YAG crystal <NUM> is a right prism. Optionally, flat Nd:YAG crystal <NUM> is a right rectangular prism. Any one or more of the aforementioned surfaces of flat Nd:YAG crystal <NUM> may be facets. In the example of <FIG>, the thickness of flat Nd:YAG crystal <NUM> is substantially constant, and is denoted "H". In the example of <FIG>, the internal reflections within flat Nd:YAG crystal <NUM> are reflected only from first side surface <NUM> and from second side surface <NUM>, but this is not necessarily so, and light may be internally reflected from any surface of flat Nd:YAG crystal <NUM> before being emitted as the outgoing laser light.

In addition to flat Nd:YAG crystal <NUM>, GM amplifier <NUM> may also optionally include optional pump light source <NUM>, which emits the pump light that has at least the first frequency. Optional pump light source <NUM> may be implemented as suitable type of light source, such as LED, vertical-cavity surface-emitting laser (VCSEL), other types of lasers, and so on.

It is noted that utilization of VCSEL as a pump light source (which is made feasible by the disclosed novel geometrical format of the flat Nd:YAG crystal <NUM>) may be used for reducing the cost of the crystal amplifier when compared to prior art solutions, as well as facilitating easier and high-volume manufacturing when compared to prior art solutions.

The disclosed novel geometry in which pump light is provided over a large top surface means that the light source may have a relatively low brightness per area.

Optionally, GM amplifier <NUM> is operated in a low duty cycle (e.g., below <NUM>%, between <NUM>%-<NUM>%, between <NUM>%-<NUM>%), so as to allow GM amplifier <NUM> to cool down (which is facilitated by the relative thinness of GM amplifier <NUM>. Optionally, GM amplifier <NUM> may include cooling module <NUM> (whether an active cooling module or a passive cooling module which may be connected to a heat sink) for cooling down flat Nd:YAG crystal <NUM>, or any other part of GM amplifier <NUM>. Optionally, a surface of cooling module <NUM> may touch a corresponding surface of flat Nd:YAG crystal <NUM> (e.g., bottom surface <NUM>, as illustrated, or any other surface of the crystal). The relative thinness of flat Nd:YAG crystal <NUM> also enables doping of the crystal in relatively high doping density (e.g., above <NUM>%, between <NUM>-<NUM>%, between <NUM>-<NUM>%).

In an example not in accordance with the claimed invention, amplifier <NUM> may be a side pumped GM amplifier which is activated in a multimode mode, with optionally tens of different modes of the illumination.

Referring to GM amplifier <NUM> in its entirety, better extraction efficiency may be achieved in GM amplifier <NUM> by the combination of ceramic Nd:YAG crystal and multipass of light within it (which extends the effective path).

Optionally, a doping concentration of the Neodymium within the flat Nd:YAG crystal is lower than <NUM>%. Optionally, a doping concentration of the Neodymium within the flat Nd:YAG crystal is between <NUM>% and <NUM>%. Optionally, the top surface is coated with anti-reflective coating for at least one frequency out of: the first frequency, and the second frequency.

Optionally, the top surface is coated with anti-reflective coating for at least two frequencies out of: the first frequency, the second frequency, and the emitted light frequency. Optionally, at least one of the first side surface and the second side surface is coated with anti-reflective coating for at least one frequency out of: the first frequency, and the second frequency.

Optionally, at least one of the first side surface and the second side surface is coated with anti-reflective coating for at least two frequencies out of: the first frequency, and the second frequency. Optionally, the at least one of the first side surface and the second side surface is further coated with anti-reflective coating for an amplified spontaneous emission (ASE) frequency of the flat Nd:YAG crystal <NUM> (e.g., <NUM>,<NUM>).

<FIG> illustrate amplified laser illumination sources <NUM>, which includes GM amplifier <NUM> and a seed laser <NUM>. Optionally, the seed laser may be an Nd:YAG based laser emitting the light entering the flat Nd:YAG crystal via the first side surface. Optionally, any of the aforementioned lasers (e.g., passively Q-switched lasers <NUM> and <NUM>) may be used as seed laser <NUM>.

Optionally, flat Nd:YAG crystal <NUM> may be a co-doped crystal in which the YAG crystal (or at least one or more parts thereof) is doped by neodymium and further doped by an additional material. The additional material may be a material which, when doping the YAG crystal, suppresses light in at least one ASE frequency of the flat Nd:YAG crystal <NUM>. For example, chromium (Cr), and especially chromium ions (e.g., Cr<NUM>+) may be used to suppress emission at <NUM>,<NUM>. Further doping the flat Nd:YAG crystal <NUM> with chromium may increase the yield of the amplifier. Other materials may also be used (e.g., Co<NUM>+).

Referring to implementations in which some or all of the side surfaces are not perpendicular to the top surface, it is noted that an angle between a side surface and the top surface (and/or the bottom surface) may be selected which reduces the affect of ASE, and the degree to which ASE will be amplified within the flat Nd:YAG crystal <NUM>.

While certain features of the disclosure have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the scope of the appended claims.

It will be appreciated that the embodiments described above are cited by way of example, and various features thereof and combinations of these features can be varied and modified.

Claim 1:
A gain medium amplifier (<NUM>), the gain medium amplifier comprising:
a flat neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal (<NUM>), having an average thickness of less than <NUM> millimeters, the flat Nd:YAG crystal comprising:
a top surface (<NUM>)through which pump light having a first frequency may enter the flat Nd:YAG crystal, the first frequency being between <NUM> and <NUM>, wherein the top surface has a rectangular shape having a longer first dimension and a shorter second dimension orthogonal to the first dimension, and wherein the longer first dimension is at least <NUM> times longer than the average thickness of the flat Nd:YAG crystal;
a bottom surface (<NUM>) opposing the top surface;
a first side surface (<NUM>), through which incoming laser light having a second frequency may enter the flat Nd:YAG crystal, the second frequency being between <NUM>,<NUM> and <NUM>,<NUM>; and
a second side surface (<NUM>) opposite the first side surface through which outgoing laser light having the second frequency may be emitted from the flat Nd:YAG crystal after being internally reflected by the first and second side surfaces of the flat Nd:YAG crystal, wherein a power of the outgoing laser light is at least <NUM> times stronger than a power of the incoming laser light after being amplified using the pump light, wherein the first and second side surfaces correspond to the longer sides of the rectangular shape of the top surface of the flat Nd:YAG crystal.