IL289719B2

IL289719B2 - Scaled phase modification, phase calibration and seed laser protection in optical phased array

Info

Publication number: IL289719B2
Application number: IL289719A
Authority: IL
Inventors: Shekel Eyal; Vidne Yaniv; Urbach Benayahu; Shapira Avisar
Original assignee: Civan Advanced Tech Ltd; Shekel Eyal; Vidne Yaniv; Urbach Benayahu; Shapira Avisar
Priority date: 2022-01-10
Filing date: 2022-01-10
Publication date: 2023-07-01
Also published as: IL289719A; IL289719B1

Description

SCALED PHASE MODIFICATION, PHASE CALIBRATION AND SEED LASER PROTECTION IN OPTICAL PHASED ARRAY FIELD OF THE INVENTION The present invention relates generally to laser coherent beam combining and more particularly to optical phased arrays. . BACKGROUND OF THE INVENTION Various types of optical phased arrays are known in the art.

SUMMARY OF THE INVENTION The present invention seeks to provide systems and methods relating to scaled phase modification and phase calibration of dynamically shaped laser beams produced by laser optical phased arrays as well as systems and methods for protection of damage to seed lasers in optical phased arrays or in other laser systems. There is thus provided in accordance with a preferred embodiment of the present invention a laser system including a seed laser, a laser beam splitting and combining subsystem receiving an output from the seed laser, splitting the output into a plurality of sub-beams and providing a combined laser output including the plurality of sub-beams and a phase modulation subsystem grouping at least a portion of ones of the plurality of sub-beams into a multiplicity of groups of sub-beams, the phase modulation subsystem, in parallel across the multiplicity of groups of sub-beams, varying a phase of each sub-beam within each group relative to phases of other sub-beams within the group so as to vary a phase of each group, and varying the phase of each group relative to phases of other ones of the multiplicity of groups, thereby varying a phase of the combined laser output. Preferably, the phase modulation subsystem includes at least one cylindrical lens for performing the grouping. Alternatively, the phase modulation subsystem includes an array of mirrors and corresponding focusing lenses for performing the grouping. Preferably, the phase modulation subsystem includes a plurality of phase modulators for varying the phases of the sub-beams. Preferably, the phase modulation subsystem includes at least one electronic control module in operative control of the plurality of phase modulators. Preferably, the phase modulation subsystem includes a multiplicity of detectors corresponding to the multiplicity of groups, for detecting a far field intensity pattern of each of the multiplicity of groups. Preferably, the multiplicity of detectors performs the detecting at least partially mutually simultaneously. 30 Preferably, the phase modulation subsystem includes an additional auxiliary detector for detecting a combined far field intensity pattern of the multiplicity of groups. In accordance with a preferred embodiment of the present invention, the phase modulation subsystem includes a multiplicity of additional phase modulators, each additional phase modulator being common to all sub-beams within each the group for varying the phase of each group relative to phases of other ones of the multiplicity of groups. Preferably, the phase modulation subsystem includes an additional electronic control module in operative control of the multiplicity of additional phase modulators. Preferably, the varying of the phase of the combined laser output includes maximizing an intensity of the combined laser output. Preferably, the varying of the phase of the combined laser output provides spatial modulation of the combined laser output, without involving mechanical spatial modulation of the combined laser output. In accordance with another preferred embodiment of the present invention, the laser beam splitting and combining subsystem provides laser beam amplification downstream of the splitting and upstream of the combining. There is also provided in accordance with a further preferred embodiment of the present invention a method for performing phase variation of a laser output including receiving a laser output from a seed laser, splitting the laser output into a plurality of sub-beams and combining the plurality of sub-beams to provide a combined laser output, grouping at least a portion of ones of the plurality of sub-beams into a multiplicity of groups of sub-beams, in parallel across the multiplicity of groups of sub-beams, varying a phase of each sub-beam within each group relative to phases of other sub-beams within the group so as to vary a phase of each group and varying the phase of each group relative to phases of other ones of the multiplicity of groups, thereby varying a phase of the combined laser output. Preferably, the grouping is performed by at least one cylindrical lens. Alternatively, the grouping is performed by an array of mirrors and corresponding focusing lenses.

Preferably, the varying of the phases of the sub-beams is performed by a plurality of phase modulators. Preferably, the method also includes controlling the plurality of phase modulators by at least one electronic control module. Preferably, the method also includes detecting a far field intensity pattern of each of the multiplicity of groups, by a corresponding multiplicity of detectors. Preferably, the detecting is performed at least partially mutually simultaneously for the multiplicity of groups. Preferably, the method also includes detecting a combined far field intensity pattern of the multiplicity of groups, by an auxiliary detector. In accordance with a preferred embodiment of the present invention, the varying of the phase of each group relative to phases of other ones of the multiplicity of groups is performed by a multiplicity of additional phase modulators, each additional phase modulator being common to all sub-beams within each the group. Preferably, the method also includes controlling the multiplicity of additional phase modulators by an additional electronic control module. Preferably, the varying of the phase of the combined laser output includes maximizing an intensity of the combined laser output. Preferably, the varying of the phase of the combined laser output provides spatial modulation of the combined laser output, without involving mechanical spatial modulation of the combined laser output. In accordance with another preferred embodiment of the present invention, the method also includes amplifying the laser output downstream of the splitting and upstream of the combining. There is additionally provided in accordance with yet another preferred embodiment of the present invention a laser system including a seed laser, a laser splitting and combining subsystem receiving an output from the seed laser and combining the output to provide a combined laser output, a phase modulation subsystem for varying a phase of the combined laser output and a voltage-to-phase correlation subsystem for correlating a voltage applied to the phase modulation subsystem to a phase modulating output produced by the phase modulation subsystem and for providing a voltage-to-phase correlation output useful in calibrating the phase modulation subsystem, the correlating being performed periodically during the varying of the phase. Preferably, the phase modulation subsystem includes a plurality of phase modulators. Preferably, the voltage is applied to the plurality of phase modulators by a phase modulation control module. Preferably, the voltage includes a voltage intended to produce a phase shift of the combined laser output of 2?. Preferably, the correlating includes measuring a change in intensity of a far-field intensity pattern of the combined laser output following application of the voltage and deriving a relationship between the voltage and a phase shift corresponding to the change in intensity. Preferably, the voltage is sequentially applied to ones of the plurality of phase modulators. Preferably, the correlating is performed at a slower rate than the varying of the phase. Preferably, the varying of the phase is performed at a rate of 1 million times per second and the correlating is performed at a rate of once per second. There is further provided in accordance with still another preferred embodiment of the present invention a method for performing phase calibration of a laser system including receiving an output from a seed laser, splitting and combining the output to provide a combined laser output, varying a phase of the combined laser output by a phase modulation subsystem, periodically during the varying of the phase, applying a voltage to the phase modulation subsystem and correlating the voltage to a phase modulating output produced by the phase modulation subsystem, and providing a voltage-to-phase correlation output useful in calibrating the phase modulation subsystem. Preferably, the phase modulation subsystem includes a plurality of phase modulators. Preferably, the applying the voltage is performed by a phase modulation control module.

Preferably, the voltage includes a voltage intended to produce a phase shift of the combined laser output of 2?. Preferably, the correlating includes measuring a change in intensity of a far-field intensity pattern of the combined laser output following application of the voltage and deriving a relationship between the voltage and a phase shift corresponding to the change in intensity. Preferably, the method also includes sequentially applying the voltage to ones of the plurality of phase modulators. Preferably, the correlating is performed at a slower rate than the varying of the phase. Preferably, the varying of the phase is performed at a rate of 1 million times per second and the correlating is performed at a rate of once per second. There is also provided in accordance with yet a further preferred embodiment of the present invention a laser amplifier system including a seed laser providing a first laser output having a first power, an amplifying subsystem receiving the first laser output from the seed laser and providing an amplified laser output and an auxiliary laser subsystem providing a second laser output at least upon cessation of the first laser output, the second laser output having a second power lower than the first power. Preferably, the auxiliary laser subsystem includes an additional seed laser providing the second laser output to the amplifying subsystem at least concurrently with the providing of the first laser output. Additionally or alternatively, the amplifying subsystem includes an entry at which the first laser output is received and an exit at which the amplified laser output is provided and the laser amplifier system includes a first reflection grating positioned at the entry and a second reflection grating positioned at the exit, the first and second reflection gratings in combination with the amplifying subsystem including the auxiliary laser subsystem. Preferably, the first and second reflection gratings are reflective in a wavelength range of 1090nm – 1100nm. Preferably, the second laser output is of a different wavelength than the first laser output.

Preferably, the system also includes a filter downstream of the seed laser and upstream of the amplifying subsystem. In accordance with a preferred embodiment of the present invention, the filter structure includes a beam splitter splitting the first laser output along a first and a second optical path, the first optical path being longer than the second optical path, a detector detecting a combined laser output from the first and second optical paths, an electronic control module coupled to the detector, for receiving an output from the detector and a phase control module located along one of the first and second optical paths, the phase control module being operated by the electronic control module to modify a phase of the first laser output responsive to detection by the detector of interference in the combined laser output. Preferably, the system also includes a detector subsystem for detecting the first laser output from the seed laser. In accordance with a preferred embodiment of the present invention, the detector subsystem includes a splitter splitting the first laser output into a first portion and a second portion, an additional amplifier amplifying the second portion and providing an amplified output and an optical fiber receiving the amplified output, the optical fiber being configured to exhibit non-linear effects upon a line width of the first laser output becoming unacceptably narrow. Preferably, the optical fiber has a length of 25 m and a core diameter of 6 microns. There is still further provided in accordance with another preferred embodiment of the present invention a method for preventing damage to an amplifier in a laser system including providing a first laser output having a first power, amplifying the first laser output by an amplifier, to provide an amplified laser output and providing a second laser output at least upon cessation of the providing of the first laser output, the second laser output having a second power lower than the first power. Preferably, the providing of the second laser output is performed at least concurrently with the providing of the first laser output. Additionally or alternatively, the amplifier includes an entry at which the first laser output is received and an exit at which the amplified laser output is provided, and the method also includes positioning a first reflection grating at the entry and a second reflection grating at the exit, the first and second reflection gratings in combination with the amplifier providing the second laser output. Preferably, the first and second reflection gratings are reflective in a wavelength range of 1090nm-1100nm. Preferably, the second laser output is of a different wavelength than the first laser output. Preferably, the method also includes filtering the first laser output upstream of the amplifying of the first laser output. In accordance with a preferred embodiment of the present invention the filtering includes splitting the first laser output along a first and a second optical path, the first optical path being longer than the second optical path, detecting by a detector a combined laser output from the first and second optical paths, receiving, by an electronic control module, an output from the detector and modifying a phase of the first laser output along one of the first and second optical paths, based on the output from the detector and responsive to detection by the detector of interference in the combined laser output. Preferably, the method also includes detecting the first laser output. In accordance with a preferred embodiment of the present invention, the detecting includes splitting the first laser output into a first portion and a second portion, amplifying the second portion and providing an amplified output and receiving the amplified output by an optical fiber, the optical fiber being configured to exhibit non-linear effects upon a line width of the first laser output becoming unacceptably narrow. Preferably, the optical fiber has a length of 25 m and a core diameter of microns. 25 BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated more fully based on the following detailed description taken in conjunction with the drawings in which: Fig. 1 is a simplified schematic plan view illustration of an optical phased array laser system including scaled phase modification of dynamic beams, constructed and operative in accordance with a preferred embodiment of the present invention; Fig. 2 is a simplified schematic plan view illustration of an optical phased array laser system including scaled phase modification of dynamic beams, constructed and operative in accordance with another preferred embodiment of the present invention; Figs. 3A and 3B are simplified top and perspective views of an optical phased array laser system including scaled phase modification of dynamic beams of a type illustrated in Fig. 1 or Fig. 2; Fig. 4 is a simplified schematic plan view illustration of an optical phased array laser system including scaled phase modification of dynamic beams, constructed and operative in accordance with a further preferred embodiment of the present invention; Fig. 5 is a simplified schematic plan view illustration of an optical phased array laser system including scaled phase modification of dynamic beams, constructed and operative in accordance with yet a further preferred embodiment of the present invention; Figs. 6A and 6B are simplified top and perspective views of an optical phased array laser system including scaled phase modification of dynamic beams of a type illustrated in Fig. 4 or Fig. 5; Fig. 7 is a simplified schematic plan view illustration of an optical phased array laser system including scaled phase modification of dynamic beams, constructed and operative in accordance with a still further preferred embodiment of the present invention; 30 Fig. 8 is a simplified schematic illustration of an optical phased array laser system including voltage-phase correlating functionality, constructed and operative in accordance with another preferred embodiment of the present invention; Fig. 9 is a flow chart illustrating steps for performing voltage-phase correlation in a system of the type illustrated in Fig. 8; Fig. 10 is a simplified schematic illustration of a laser amplification system including a seed laser failure protection system constructed and operative in accordance with a preferred embodiment of the present invention; Fig. 11 is a simplified schematic illustration of a laser amplification system including a seed laser failure protection system constructed and operative in accordance with another preferred embodiment of the present invention; Fig. 12 is a simplified schematic illustration of a laser amplification system including a seed laser failure protection system constructed and operative in accordance with yet another preferred embodiment of the present invention; Fig. 13 is a simplified schematic illustration of a laser amplification system including a seed laser failure protection system constructed and operative in accordance with yet a further preferred embodiment of the present invention; Fig. 14 is a simplified schematic illustration of a filter suitable for use in a laser amplification system of any of the types illustrated in Figs. 10 – 13; and Fig. 15 is a simplified schematic illustration of a sensor useful in a laser amplification system of any of the types illustrated in Figs. 10 – 13. 30 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Reference is now made to Fig. 1, which is a simplified schematic plan view illustration of an optical phased array laser system including scaled phase modification of dynamic beams, constructed and operative in accordance with a preferred embodiment of the present invention. As seen in Fig. 1, there is provided an optical phased array (OPA) laser system 100. OPA laser 100 may be of a type generally described in related Israel Patent Application no. 255496, assigned to the same assignee as the present invention. OPA laser 100 preferably comprises a seed laser 102 and a laser beam splitting and combining subsystem 104. Splitting and combining subsystem 104 preferably receives an output laser beam from seed laser 102 and splits the output laser beam into a plurality of sub-beams along a corresponding plurality of channels 106. Here, by way of example only, an output from seed laser 102 may be split into a 4 x 4 matrix of 16 sub-beams along 16 corresponding channels 106, four of which sub-beams and channels 106 are seen in the top view of OPA laser 100 in Fig. 1. It is appreciated, however, that splitting and combining subsystem 104 may include a fewer or greater number of channels along which the output of seed laser 102 is split, and typically may include a far greater number of channels such as 32 or more channels. The relative phase of each sub-beam may be individually modulated by a phase modulator 108, preferably located along each of channels 106. Each phase modulated sub-beam produced by the splitting and subsequent phase modulation of the output of seed laser 102 preferably propagates towards a collimating lens 109. The individually collimated, phase modulated sub-beams are subsequently combined, for example at a focal plane of lens 110, to form an output beam 112. Splitting and combining subsystem 104 may also provide laser amplification of the sub-beams, preferably following the splitting of the output beam of seed laser 102 into sub-beams and prior to the combining of the sub-beams to form output beam 112. Here, by way of example, splitting and combining subsystem 104 is shown to include a plurality of optical amplifiers 114 located along corresponding ones of channels 106 for amplifying each sub-beam. It is appreciated, however, that such amplification is optional and may be omitted, depending on the power output specifications of OPA laser 100. The phase of output beam 112, and hence the position and shape of the far-field intensity pattern thereof, is controlled, at least in part, by the relative phases of the constituent sub-beams combined to form output beam 112. In many applications, such as laser cutting, laser welding, free-space optical communications and laser additive manufacturing, it is desirable to dynamically move and shape the far-field intensity pattern of the output beam. As described in related Israel Patent Application No. 225496, dynamic variation of parameters of the output beam may be achieved by dynamically varying the relative phases of the individual sub-beams along channels 106 and thereby varying the phase of the combined laser output 112 so as to dynamically control the position and shape of the far-field intensity pattern thereof. In the case of OPA laser 100 including a large number of individual sub-beams, phase measurement and corresponding phase modification of each sub-beam with respect to the phases of all of the other ones of the sub-beams, may be challenging due to the large number of individual sub-beams involved. Specifically, due to the large number of individual sub-beams contributing to the combined output 112, the time taken to measure and modify the phase of each individual sub-beam with respect to the other sub-beams so as to dynamically control the phase of the combined laser output 112 may be unacceptably long. Furthermore, the signal to noise ratio may be unacceptably low. It is a particular feature of a preferred embodiment of the present invention that OPA laser 100 preferably includes a phase modulation subsystem 120 for carrying out phase modulation of the combined laser output in a scaled manner. More specifically, phase modulation subsystem 120 preferably groups at least a portion of the sub-beams provided by laser splitting and combining subsystem 104 into groups and then performs phase modulation within each group of sub-beams, only with respect to other sub-beams within the group. Such group phase modulation is preferably performed in parallel across various individual groups of sub-beams. Phase modulation subsystem 120 then preferably optimizes the phase of each group of sub-beams with respect to the phases of other ones of the groups of sub-beams, in order to vary the phase of the combined laser output 112, in a manner detailed henceforth.

Phase modulation subsystem 120 preferably includes a phase control electronic module 130 in operative control of phase modulators 108. Phase control electronic module 130 preferably controls each phase modulator 108 so as to dynamically modulate the relative phases of the sub-beams along channels 106, in accordance with the desired far-field intensity pattern of output beam 112, as ascertained by phase modulation subsystem 120. In order to facilitate application of phase variation to output beam 112, a portion of the output of OPA laser 100 is preferably extracted and directed towards a plurality of detectors 150. The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required phase variation may be calculated. In the embodiment shown in Fig. 1, plurality of sub-beams along channels 106 are directed towards a beam splitter 160. Beam splitter 160 preferably splits each sub-beam into a transmitted portion 162 and a reflected portion 164 in accordance with a predetermined ratio. For example, beam splitter 160 may split each sub-beam with a 99.9% transmitted: 0.01% reflected ratio. The transmitted portion 162 of the sub-beams preferably propagates towards focal lens 110, at which focal lens 110 the sub-beams are combined to form output beam 112 having a far-field intensity pattern 166. The reflected portion 164 of the sub-beams preferably propagates towards a cylindrical lens 168. Cylindrical lens 168 is preferably operative to receive the reflected portion 164 of the sub-beams and group the sub-beams into a multiplicity of groups, by converging the sub-beams along a direction of curvature of lens 168. Here, by way of example, the sub-beams are shown to be converged into four groups 170, each group 170 being made up of four sub-beams. Preferably, each group 170 of sub-beams grouped by cylindrical lens 1forms a beam having a far-field intensity pattern 172 incident on a surface of corresponding one of plurality of detectors 150. Each detector 150 preferably samples the group far-field intensity pattern 172 incident thereon. Each detector 150, in cooperation with a corresponding control electronics sub-module 174 included in control module 130, then preferably optimizes the relative phases of the sub-beams within the group of sub-beams 170 sampled thereby, with respect to the phases of the other sub-beams within the group 170. Such sampling and optimization is preferably carried out in parallel and preferably simultaneously for ones of far-field intensity patterns 172 across all of detectors 150. Various algorithms suitable for phase optimization include sequential or non-sequential optimization algorithms, such as described in related Israel Patent Application no. 2554 In order to optimize the relative phase of each of groups 170 with respect to other ones of groups 170, a portion of groups 170 is preferably directed, by way of an auxiliary beam splitter 180, to an auxiliary cylindrical lens 182. Auxiliary cylindrical lens 182 preferably causes groups of sub-beams 170 to converge into a single beam 1incident on an auxiliary detector 186. Auxiliary detector 186 preferably receives thereat a single beam having a far field intensity pattern corresponding to that of a combination of all of groups of sub-beams 170. Auxiliary detector 186 preferably samples and optimizes the phases of groups 170 with respect to each other, in cooperation with phase control electronics included in electronic control module 130. Particularly preferably, one function of phase control electronic module 130 is to control each phase modulator 108 so as to apply a phase shift maximizing the total power on auxiliary detector 186. It is appreciated that carrying out phase modulation in the above- described scaled manner, wherein the phase of each sub-beam is optimized with respect to the phases of other sub-beam members of its group 170 and the phases of groups 1are then subsequently optimized with respect to each other so as to vary the phase of the combined laser output 112, is far quicker and less complex than optimizing the phase of each individual sub-beam with respect to the phases of all of the other sub-beams in OPA 100. Furthermore, this allows the phase optimization to be carried out by individual sets of control electronics in each control electronics sub-module 1coupled to each detector 150, rather than requiring a single set of control electronics and improves the signal to noise ratio. It is appreciated that the functionality of optimizing the relative phase of each of groups 170 with respect to other ones of groups 170 may alternatively be carried out by additional group phase modulators, operative to modulate the collective phase of each of groups 170, rather than by individual phase modulators 108 operative to modulate the individual phase of each sub-beam member of each of groups 170. An exemplary implementation of such an arrangement is illustrated in Fig. 2 and may generally resemble the phase modulation arrangement described in US Patent No. 9,893,494 in some aspects thereof.

As seen in Fig. 2, system 100 may be modified by adding a series of group phase modulators corresponding to the number of groups 170. Here, by way of example, system 100 comprises 16 sub-beams, four of which sub-beams are included in each of four groups 170, such that a total of four additional group phase modulators 2may be included in system 100, as seen in Fig. 2. Each group phase modulator 208 is preferably common to the four channels 106 forming part of each group 170 and provides a phase shift optimizing the collective group phase of the sub-beams along the four channels 106. Preferably, ones of group phase modulator 208 are controlled by an additional control sub-module 274, preferably included in control module 130. Auxiliary detector 186 is preferably coupled to the additional control sub-module 274. It is appreciated that optimizing the relative phases of groups 170 with respect to each other by group phase modulators 208 rather than by individual sub-beam phase modulators 108 may be more efficient and may simplify the phase modulation process, but requires the employment of additional phase modulating and circuitry elements, thus increasing the cost and complexity of system 100. Variation of the phase of combined laser output 112 preferably provides spatial modulation of the output 112. It is appreciated that, due to the scaled nature of the phase modulation carried out by phase modulation subsystem 120, the phase of combined laser output 112 may be varied very rapidly, at a rate greater than that achievable by mechanical spatial modulation mechanisms. The spatial modulation provided by OPA laser 100 may optionally be augmented by additional mechanical spatial modulation mechanisms, as are known in the art, or may not involve mechanical spatial modulation. It is understood that the particular structure and configuration of optical elements shown herein, including beam splitter 160, focal lens 110, cylindrical lens 168, auxiliary beam splitter 180 and auxiliary cylindrical lens 182 is exemplary only and depicted in a highly simplified form. It is appreciated that OPA laser system 100 may include a variety of such elements, as well as additional optical elements, including, by way of example only, additional or alternative lenses, optical fibers and coherent free- space far-field combiners.

Furthermore, it is appreciated that cylindrical lens 168 may have optical properties so as to group the individual sub-beams into mutually similar or identical groups comprising equal numbers of sub-beams. Alternatively, cylindrical lens 168 may have optical properties so as to group the individual sub-beams into mutually differing groups comprising different numbers of sub-beams. An exemplary implementation of an OPA laser system of the type illustrated in Fig. 1 or Fig. 2 is shown in Figs. 3A and 3B. Turning now to Figs. 3A and 3B, an OPA laser system 300 is provided wherein an output laser beam from a seed laser (not shown) such as seed laser 102 is split into a plurality of sub-beams along a corresponding plurality of channels 306. By way of example, the laser output may be split, by way of example, into a 10 x 10 matrix of 100 sub-beams along 1corresponding channels 306. It is appreciated that, for the sake of clarity of presentation, only selected ones of the sub-beams are illustrated in Fig. 3B. Sub-beams along channels 306 may subsequently be collimated and focused by collimating and focusing elements (not shown) such as collimating and focusing lenses 109, 110, to produce a combined output beam. In order to facilitate application of phase variation to the output beam, a portion of the output of OPA laser 300 is preferably extracted and directed towards a plurality of detectors 350. The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required phase variation may be calculated. In the embodiment shown in Figs. 3A and 3B, plurality of sub-beams along channels 306 are directed towards a beam splitter 360. Beam splitter 3preferably splits each sub-beam into a transmitted portion 362 and a reflected portion 364 in accordance with a predetermined ratio. The transmitted portion 362 of the sub-beams is preferably combined to form the output beam. The reflected portion 364 of the sub-beams is preferably reflected towards a cylindrical lens 368, which cylindrical lens 368 is particularly preferred embodiment of cylindrical lens 168. Cylindrical lens 368 is preferably operative to receive the reflected portion 364 of the sub-beams and cause the sub-beams to converge into a multiplicity of groups along a direction of curvature of cylindrical lens 368. By way of example, in the case of 100 sub-beams, cylindrical lens 368 may cause the sub-beams to converge into ten groups 370 of ten sub-beams.

Preferably, each group 370 of sub-beams grouped by cylindrical lens 3forms a beam having a far field intensity pattern incident on a surface of corresponding one of plurality of detectors 350. By way of example plurality of detectors 350 may include ten detectors 350, each sampling a group beam comprising ten individual sub-beams. Each detector 350, in cooperation with a corresponding control electronics module (not shown) such as control module 130, then preferably optimizes the phases of the sub-beams included in the group 370 of sub-beams sampled thereby, Such sampling and optimization is preferably carried out in parallel and preferably simultaneously across all of detectors 350. In order to optimize the relative phase of each of groups 370 with respect to the phases of other ones of groups 370, a portion of groups 370 is preferably directed, by way of an auxiliary beam splitter 380, to an auxiliary cylindrical lens 382. It is appreciated that auxiliary cylindrical lens 382 is a particularly preferred embodiment of auxiliary cylindrical lens 182. Auxiliary cylindrical lens 382 preferably focuses groups of sub-beams 370 into one combined beam 384 incident on an auxiliary detector 386. Auxiliary detector 386 preferably receives thereat a far field intensity pattern corresponding to that of a combination of all of groups of sub-beams 370 and samples and optimizes the phases of groups 370 with respect to each other, in cooperation with phase control electronics. It is appreciated that the optimization of the phases of groups 370 with respect to each other may be by way of phase modulation of the phases of the individual sub-beams by phase modulators 108, as described hereinabove with reference to Fig. 1, or may be by way of phase modulation of the phases of the groups of sub-beams by group phase modulators 208, as described hereinabove with reference to Fig. 2. Reference is now made to Fig. 4, which is a simplified schematic plan view illustration of an optical phased array laser system including scaled phase modification of dynamic beams, constructed and operative in accordance with a preferred embodiment of the present invention. As seen in Fig. 4, there is provided an optical phased array (OPA) laser system 400. OPA laser 400 may be of a type generally described in related Israel application no. 255496, assigned to the same assignee as the present invention. OPA laser 400 preferably comprises a seed laser 402 and a laser beam splitting and combining subsystem 404. Splitting and combining subsystem 404 preferably receives an output laser beam from seed laser 402 and splits the output laser beam into a plurality of sub-beams along a corresponding plurality of channels 406. Here, by way of example only, an output from seed laser 402 may be split into a 4 x 4 matrix of 16 sub-beams along 16 corresponding channels 406, four of which sub-beams and channels 406 are seen in the top view of OPA laser 400 in Fig. 4. It is appreciated, however, that splitting and combining subsystem 404 may include a fewer or greater number of channels along which the output of seed laser 402 is split, and typically may include a far greater number of channels such as 32 or more channels. The relative phase of each sub-beam may be individually modulated by a phase modulator 408, preferably located along each of channels 406. Each phase modulated sub-beam produced by the splitting and subsequent phase modulation of the output of seed laser 402 preferably propagates towards a collimating lens 409. The individually collimated, phase modulated sub-beams are subsequently combined, for example at a focal plane of a lens 410, to form an output beam 412. Splitting and combining subsystem 404 may also provide laser amplification of the sub-beams, preferably following the splitting of the output beam of seed laser 402 into sub-beams and prior to the combining of the sub-beams to form output beam 412. Here, by way of example, splitting and combining subsystem 404 is shown to include a plurality of optical amplifiers 414 located along corresponding ones of channels 406 for amplifying each sub-beam. It is appreciated, however, that such amplification is optional and may be omitted, depending on the power output requirements of OPA laser 400. The phase of output beam 412, and hence the position and shape of the far-field intensity pattern thereof, is controlled, at least in part, by the relative phases of the constituent sub-beams combined to form output beam 412. In many applications, such as laser cutting, laser welding, free-space optical communications and laser additive manufacturing, it is desirable to dynamically move and shape the far-field intensity pattern of the output beam. As described in related Israel Patent Application No. 225496, dynamic variation of parameters of the output beam may be achieved by dynamically varying the relative phases of the individual sub-beams along channels 406 and thereby varying the phase of the combined laser output 412 so as to dynamically control the position and shape of the far-field intensity pattern thereof. In the case of OPA laser 400 including a large number of individual sub-beams, phase measurement and corresponding phase modification of each sub-beam with respect to the phases of all of the other ones of the sub-beams, may be challenging due to the large number of individual sub-beams involved. Specifically, due to the large number of individual sub-beams contributing to the combined output 412, the time taken to measure and modify the phase of each individual sub-beam with respect to the other sub-beams so as to dynamically control the phase of the combined laser output 412 may be unacceptably long. Furthermore, the signal to noise ratio may be unacceptably low. It is a particular feature of a preferred embodiment of the present invention that OPA laser 400 preferably includes a phase modulation subsystem 420 for carrying out phase modulation of the combined laser output in a scaled manner. More specifically, phase modulation subsystem 420 preferably groups at least a portion of the sub-beams provided by laser splitting and combining subsystem into groups and then performs phase modulation within each group of sub-beams, only with respect to the phases of other sub-beams within the group. Such group phase modulation is preferably performed in parallel across various individual groups. Phase modulation subsystem 420 then preferably optimizes the phase of each group of sub-beams with respect to the phases of other ones of the groups of sub-beams, in order to vary the phase of the combined laser output 412, in a manner detailed henceforth. Phase modulation subsystem 420 preferably includes a phase control electronic module 430 in operative control of phase modulators 408. Phase control electronic module 430 preferably controls each phase modulator 408 so as to dynamically modulate the relative phases of the sub-beams along channels 406, in accordance with the desired far-field intensity pattern of output beam 412 and as ascertained by phase modulation subsystem 420. In order to facilitate application of phase variation to output beam 412, a portion of the output of OPA laser 400 is preferably extracted and directed towards a plurality of detectors 450. The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required phase variation may be calculated. In the embodiment shown in Fig. 4, plurality of sub-beams along channels 406 are directed towards a beam splitter 460. Beam splitter 460 preferably splits each sub-beam into a transmitted portion 462 and a reflected portion 464 in accordance with a predetermined ratio. For example, beam splitter 460 may split each sub-beam with a 99.9% transmitted: 0.01% reflected ratio. The transmitted portion 462 of the sub-beams preferably propagates towards focal lens 410, at which focal lens 410 the sub-beams are combined to form output beam 412 having a far-field intensity pattern 466. The reflected portion 464 of the sub-beams is preferably reflected towards an array of mirrors 468, each mirror 4being positioned in spaced relation to a corresponding focusing lens 469. By way of example, array of mirrors 468 may comprise four mirrors 468 positioned in spaced relation to four focusing lenses 469, two of which mirrors and focusing lenses are visible in the top view of system 400 in Fig. 4. Mirrors 468 are preferably angled so as to be operative to reflect sub-beams incident thereon towards the corresponding focusing lens 469 and thereby group the reflected portion 464 of the sub-beams into a multiplicity of groups, here embodied, by way of example, as four groups 470, each group 470 including four sub-beams, two of which groups are seen in Fig. 4. Preferably, each group of sub-beams reflected at each of mirrors 468 is focused by the corresponding focal lens 469 to form a single beam comprising group of sub-beams 470 and having a far-field intensity pattern 472 incident on a surface of a corresponding one of plurality of detectors 450. Each detector 450, in cooperation with a corresponding control electronics sub-module 474 included in control module 430, then preferably optimizes the relative phases of the sub-beams within the group of sub-beams 470 sampled thereby, with respect to the phases of the other sub-beams within the group 470. Such sampling and optimization is preferably carried out in parallel and preferably simultaneously for ones of far-field intensity patterns 472 across all of detectors 450. Various algorithms suitable for phase optimization include sequential or non-sequential optimization algorithms, as described in related Israel Patent Application no. 255496 In order to optimize the relative phase of each of groups 470 with respect to other ones of groups 470, a portion of reflected portion 464 is preferably directed, by way of an auxiliary beam splitter 480, to an auxiliary cylindrical lens 482. Auxiliary cylindrical lens 482 preferably causes the sub-beams incident thereon to converge into a single beam 484 incident on an auxiliary detector 486. Auxiliary detector 486 preferably receives thereat a single beam having a far field intensity pattern corresponding to that of a combination of all of groups of sub-beams 470. Auxiliary detector 486 preferably samples and optimizes the phases of groups 470 with respect to each other, in cooperation with phase control electronics included in electronic control module 430. Particularly preferably, one function of phase control electronic module 430 is to control each phase modulator 408 so as to apply a phase shift maximizing the total power on auxiliary detector 486. It is appreciated that carrying out phase modulation in the above-described scaled manner, wherein the phase of each sub-beam is optimized with respect to the phases of other sub-beam members of its group 470 and the phases of groups 4are then subsequently optimized with respect to each other to vary the phase of the combined laser output 412, is far quicker and less complex than optimizing the phase of each individual sub-beam with respect to the phases of all of the other sub-beams in OPA. Furthermore, this allows the phase optimization to be carried out by individual sets of control electronics in each control electronics sub-module 474 coupled to each detector 350, rather than requiring a single set of control electronics and improves the signal to noise ratio. It is appreciated that the functionality of optimizing the relative phase of each of groups 470 with respect to other ones of groups 470 may alternatively be carried out by additional group phase modulators, operative to modulate the collective phase of each of groups 470, rather than by individual phase modulators 408 operative to modulate the individual phase of each sub-beam member of each of groups 470. An exemplary implementation of such an arrangement is illustrated in Fig. 5 and may generally resemble the phase modulation arrangement described in US Patent No. 9,893,494 in some aspects thereof. As seen in Fig. 5, system 400 may be modified by adding a series of group phase modulators corresponding to the number of groups 470. Here, by way of example, system 400 comprises 16 sub-beams, four of which sub-beams are included in each of four groups 470, such that a total of four additional group phase modulators 508 may be included in system 400, as seen in Fig. 5. Each group phase modulator 508 is preferably common to the four channels 406 forming part of each group 470 and provides a phase shift optimizing the collective group phase of the sub-beams along the four channels 406. Preferably, ones of group phase modulator 508 are controlled by an additional control sub-module 574, preferably included in control module 430. Auxiliary detector 486 is preferably coupled to the additional control sub-module 574. It is appreciated that optimizing the relative phases of groups 470 with respect to each other by group phase modulators 508 rather than by individual sub-beam phase modulators 408 may be more efficient and may simplify the phase modulation process, but requires the employment of additional phase modulating and circuitry elements, thus increasing the cost and complexity of system 400. Variation of the phase of combined laser output 412 preferably provides spatial modulation of the output 412. It is appreciated that, due to the scaled nature of the phase modulation carried out by phase modulation subsystem 420, the phase of combined laser output 412 may be varied very rapidly, at a rate greater than that achievable by mechanical spatial modulation mechanisms. The spatial modulation provided by OPA laser 400 may optionally be augmented by additional mechanical spatial modulation mechanisms, as are known in the art, or may not involve mechanical spatial modulation. It is understood that the particular structure and configuration of optical elements shown herein, including beam splitter 460, focal lens 410, array of mirrors 4and corresponding focal lenses 469 is exemplary only and depicted in a highly simplified form. It is appreciated that OPA laser system 400 may include a variety of such elements, as well as additional optical elements, including, by way of example only, additional or alternative lenses, optical fibers and coherent free-space far-field combiners. Furthermore, it is appreciated that mirrors 468 and corresponding focal lenses 469 may have mutually similar or identical optical properties, so as to group the individual sub-beams into mutually similar or identical groups comprising equal numbers of sub-beams. Alternatively, mirrors 468 and corresponding focal lenses 469 may have mutually different optical properties so as to group the individual sub-beams into mutually differing groups comprising different numbers of sub-beams. An exemplary implementation of an OPA laser system of the type illustrated in Fig. 4 or Fig. 5 is shown in Figs. 6A and 6B. Turning now to Figs. 6A and 6B, an OPA laser system 600 is provided wherein an output laser beam from a seed laser (not shown) such as seed laser 402 is split into a plurality of sub-beams along a corresponding plurality of channels 606. Here, by way of example only, the laser output may be split into a 10 x 10 matrix of 100 sub-beams along 100 corresponding channels 606, only selected ones of which sub-beams are illustrated in Fig. 6B for the sake of clarity of presentation. Sub-beams along channels 606 may subsequently be collimated and focused by collimating and focusing elements (not shown) such as collimating and focusing lenses 409, 410, to produce a combined output beam. In order to facilitate application of phase variation to the output beam, a portion of the output of OPA laser 600 is preferably extracted and directed towards a plurality of detectors 650. The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required phase variation may be calculated. In the embodiment shown in Figs. 6A and 6B, plurality of sub-beams along channels 606 are directed towards a beam splitter 660. Beam splitter 6preferably splits each sub-beam into a transmitted portion 662 and a reflected portion 664 in accordance with a predetermined ratio. The transmitted portion 662 of the sub-beams is preferably combined to form the output beam. The reflected portion 664 of the sub-beams is preferably reflected towards an array of mirrors 668, each mirror 668 being positioned in spaced relation to a corresponding focusing lens 669. It is appreciated that array of mirrors 668 and lenses 669 are particularly preferred embodiments of array of mirrors 468 and focusing lenses 469. Mirrors 668 are preferably angled so as to be operative to reflect sub-beams incident thereon towards the corresponding focusing lens 669 and thereby group the reflected portion 664 of sub-beams into a multiplicity of groups, here embodied, by way of example, as four groups, each group 670 including 25 sub-beams. Preferably, each set of sub-beams reflected at each of mirrors 668 is focused by the corresponding focal lens 669 to form a single beam including group of 25 sub-beams 670. Each group of sub-beams 670 is incident on a surface of corresponding one of plurality of detectors 650. Each detector 650 preferably samples the far-field intensity pattern incident thereon. Each detector 650, in cooperation with a corresponding control electronics sub-module (not shown) such as control electronics sub-module 474 included in control module 430, then preferably optimizes the phases of the sub-beams included in the group of sub-beams 670 sampled thereby, in order for the combined phases to produce a desired group far-field intensity pattern. Such sampling and optimization is preferably carried out in parallel and preferably simultaneously for ones of far-field intensity patterns across all of detectors 650. In order to optimize the relative phase of each of groups 670 with respect to other ones of groups 670, a portion of the reflected portion 664 is preferably directed, by way of an auxiliary beam splitter 680, to an auxiliary lens 682. Auxiliary lens 6preferably causes a portion of the reflected portion 664 to converge into a single beam 684 incident on an auxiliary detector 686. Auxiliary detector 686 preferably receives thereat a single beam having a far field intensity pattern corresponding to that of a combination of all of the sub-beams. Auxiliary detector 686 preferably samples and optimizes the phases of groups 670 with respect to each other, in cooperation with phase control electronics included in electronic control module 430. It is appreciated that the optimization of the phases of groups 670 with respect to each other may be by way of phase modulation of the phases of the individual sub-beams by phase modulators 408, as described hereinabove with reference to Fig. 4, or may be by way of phase modulation of the phases of the groups of sub-beams by group phase modulators 508, as described hereinabove with reference to Fig. 5. It is understood that in the above-described embodiments of OPA lasers 100, 300, 400 and 600 of Figs. 1 – 6B, phase modulation is preferably carried out in a scaled manner, with multiple detectors such as detectors 150, 350, 450 and 6employed for simultaneously performing phase measurements of sub-beams within multiple groups and a single detector, such auxiliary detector 186, 386, 486 and 686, employed for performing phase measurements of a single beam including the multiple groups. It is appreciated, however, that a system constructed and operative in accordance with a preferred embodiment of the present invention may be further scalable, to include still additional hierarchies of detectors and corresponding optical elements, depending on the number of sub-beams involved. By way of example, as shown in Fig. 7, OPA laser system 100 may be modified to include additional focusing lenses 702 for focusing groups 170 of sub-beams into intermediate groups 704 which intermediate groups are incident on intermediate detectors 706. Intermediate groups 704 are then further combined and incident on a single detector 708, at which single detector 708 intermediate groups 7are preferably phase modified with respect to each other. Reference is now made to Fig. 8, which is a simplified schematic illustration of an optical phased array laser system including voltage-phase correlating functionality, constructed and operative in accordance with another preferred embodiment of the present invention. As seen in Fig. 8, there is provided an OPA laser system 800. OPA laser 800 may be of a type generally described in related Israel Patent Application no. 255496, assigned to the same assignee as the present invention. OPA laser 800 preferably comprises a seed laser 802 and a laser beam splitting and combining subsystem 804. Splitting and combining subsystem 804 preferably receives an output laser beam from seed laser 802 and splits the output laser beam into a plurality of sub-beams along a corresponding plurality of channels 806. The relative phase of each sub-beam may be individually modulated by a phase modulator 808, preferably located along each of channels 806. Each phase modulated sub-beam produced by the splitting and subsequent phase modulation of the output of seed laser 802 preferably propagates towards a collimating lens 809. The individually collimated, phase modulated sub-beams are subsequently combined, for example at a focal plane of a lens 810, to form an output beam 812. Splitting and combining subsystem 804 may also provide laser amplification of the sub-beams, preferably following the splitting of the output beam of seed laser 802 into sub-beams and prior to the combining of the sub-beams to form output beam 812. Here, by way of example, splitting and combining subsystem 804 is shown to include a plurality of optical amplifiers 814 located along corresponding ones of channels 806 for amplifying each sub-beam. It is appreciated, however, that such amplification is optional and may be omitted, depending on the power output specifications of OPA laser 800. The phase of output beam 812, and hence the position and shape of the far-field intensity pattern thereof, is controlled, at least in part, by the relative phases of the constituent sub-beams combined to form output beam 812. In many applications, such as laser cutting, laser welding, free-space optical communications and laser additive manufacturing, it is desirable to dynamically move and shape the far-field intensity pattern of the output beam. As described in related Israel Patent Application No. 225496, dynamic variation of parameters of the output beam may be achieved by dynamically varying the relative phases of the individual sub-beams along channels 806 and thereby varying the phase of the combined laser output 812 so as to dynamically control the position and shape of the far-field intensity pattern thereof. The relative phases of the sub-beams are preferably predetermined in accordance with the desired laser output pattern. Particularly preferably, the varying relative phases are applied by a phase modulation control module 830. Phase modulation control module 830 preferably provides a voltage to phase modulators 8in order for phase modulators 808 to produce the desired phase modulation of sub-beams along channels 806. It is appreciated that phase modulation control module 8in combination with phase modulators 808 forms a particularly preferred embodiment of a phase modulation subsystem 832, which phase modulation subsystem 832 is preferably operative to vary a phase of combined laser output 812. In order to facilitate application of phase variation to output beam 812, a portion of the output of OPA laser 800 is preferably extracted and directed towards at least one detector 850. The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required phase variation may be calculated. In the embodiment shown in Fig. 8, plurality of sub-beams along channels 806 are directed towards a beam splitter 860. Beam splitter 860 preferably splits each sub-beam into a transmitted portion 862 and a reflected portion 864 in accordance with a predetermined ratio. For example, beam splitter 860 may split each sub-beam with a 99.9% transmitted: 0.01% reflected ratio. The transmitted portion 862 of the sub-beams preferably propagates towards focal lens 810, at which focal lens 810 the sub-beams are combined to form output beam 812 having a far-field intensity pattern 866. The reflected portion 864 of the sub-beams preferably propagates towards an additional focal lens 868, at which additional focal lens 868 the sub-beams are combined to form an additional reference beam 870 having a far-field intensity pattern 872 incident on a surface of detector 850. Detector 850 preferably samples the far-field intensity pattern 872 incident thereon. Detector 850, in cooperation with phase modulation subsystem 832, then preferably optimizes the relative phases of the sub-beams in order to achieve a desired far-field intensity pattern 872 and corresponding far-field intensity pattern 866. Various algorithms suitable for phase optimization include sequential or non-sequential optimization algorithms, as described in related Israel Patent Application no. 255496. In operation of phase modulation subsystem 832, phase modulation control module 830 preferably applies a voltage to each of phase modulators 808 and phase modulators 808 consequently produce a phase modulating output corresponding to the voltage applied. It is appreciated that in order for phase modulators 808 to produce the required phase shift so as to dynamically shape far-field intensity pattern 866 in accordance with a predetermined pattern, phase modulation control module 8must apply to each phase modulator 808 exactly that voltage corresponding to the specific phase modulation output required to be produced by each phase modulator 808. In order to ensure that the voltage applied by phase modulation control module 830 to phase modulators 808 produces the required and intended phase modulating output by phase modulators 808, OPA laser 800 preferably includes a voltage-to-phase correlation subsystem 880. Voltage-to-phase correlation subsystem 880 is preferably operative to correlate a voltage applied to phase modulation subsystem 832 to a phase modulating output produced by phase modulation subsystem 832 and more specifically by phase modulators 808 thereof. Furthermore, voltage-to-phase correlation subsystem 880 is preferably operative to provide a voltage-to-phase correlation output useful in calibrating phase modulation subsystem 832. Preferably, voltage-to-phase correlation subsystem performs the correlating between the voltage and phase modulating output periodically during the course of varying of the phase of combined laser output 812. It is appreciated that the inclusion of a correlation and calibration subsystem such as voltage-to-phase correlation subsystem 880 in OPA laser 800 is highly advantageous since it ensures that the voltages being applied to phase modulators 808 are indeed those voltages required to produce the desired phase shift of output beam 812 and hence shape of far-field intensity pattern 866. This is particularly important given that phase modulators suitable for use in the present invention are typically highly sensitive devices, different ones of which typically exhibit different voltage-phase relationships. Furthermore, the voltage-phase relationship of an individual phase modulator is not constant but rather may vary over time and in response to operating conditions. An exemplary voltage-phase correlation and calibration regime suitable for use in the present invention is illustrated in a flow chart 900 in Fig. 9. It is appreciated, however, that the specific steps of flow chart 900 are exemplary only and that voltage-phase correlation subsystem 880 may be implemented as any suitable subsystem within OPA laser 800 capable of calibrating phase modulation subsystem 832 periodically during the phase variation of output beam 812. Furthermore, it is appreciated that the various steps illustrated in flow chart 900 are not necessarily performed in the order shown and described and that various ones of the steps may be omitted, or may be supplemented by additional or alternative steps, as will be apparent to one skilled in the art. As seen at a first step 902, phase modulation control module 8preferably applies a voltage to phase modulators 808 in order to produce the desired phase shift of sub-beams along channels 806. The far-field intensity pattern of the reference output beam 872 is then measured at detector 850, as seen at a second step 904. The required phase shift of the sub-beams is then ascertained and a voltage again applied to phase modulators 808. The application of a voltage at first step 902 and measurement of the reference output beam 872 at second step 904 may be periodically repeated a large number of times at a given repetition rate. By way of example only, first and second steps may be repeated 20 times at a rate of 1 million times per second. Following the repetition of first and second steps 902, 904 a predetermined number of times, such as 20 times, voltage-to-phase correlation subsystem 880 may be activated. As seen a third step 906, a voltage intended to produce a phase shift of 2? is preferably applied to one phase modulator 808. As seen at a fourth step 908, the intensity of far-field intensity pattern 872 is then measured, preferably at detector 850. The phase shift of far-field intensity pattern 872 is then checked at a fifth step 910 to ascertain whether the phase shift is zero. It is understood that in the case that the voltage applied at third step 906 is indeed that voltage producing a phase shift of 2?, the phase shift of beam 812 would be zero and the intensity of far-field intensity pattern 872 would thus not change in response to the voltage applied. In this case, the phase modulator 808 to which the 2? phase shift was applied at third step 906 is found to be correctly calibrated and no additional calibration of the particular phase modulator 8is required. It is further understood that in the case that the voltage applied at third step 906 does not produce a phase shift of 2?, the phase shift of beam 812 would be non-zero and the intensity of far-field intensity pattern 872 would thus change in response to the voltage applied, as found to be the case at a seventh step 914. In this case, the relationship between the applied voltage and the resultant phase shift is preferably derived at seventh step 914. Phase modulator 808 is preferably then calibrated in accordance with the voltage-phase relationship derived at seventh step 914, as seen at an eighth step 916. As seen at a query 918, following the calibration of each phase modulator 808 at eighth calibration step 916 or ascertainment of proper calibration at fifth step 910, voltage-to-phase correlation subsystem 880 preferably checks whether a predetermined number of phase modulators 808 has been calibrated and proceeds to calibrate the next phase modulator if necessary, as seen at a ninth step 920. Voltage-to-phase correlation subsystem 880 may successively calibrate all of phase modulators 8included in system 800 or may successively calibrate a predetermined number of phase modulators 808, such as N phase modulators 808. Once the predetermined number of phase modulators 808 has been calibrated, subsystem 880 is preferably deactivated and phase variation of output beam 812 is resumed at step 902. It is understood that the frequency at which voltage-to-phase correlation subsystem 880 is activated is preferably significantly lower than the frequency at which phase variation of output beam 812 is performed. By way of example phase variation of output beam 812 may be performed 1 million times per second while voltage-to-phase correlation may be activated 1 time per second. It is further understood that the phase calibration functionality provided by voltage-to-phase correlation subsystem 880 in OPA laser 800 may alternatively be incorporated in any one of the OPA laser systems described hereinabove with reference to Figs. 1 – 7 in order to provide phase calibration in combination with a scaled phase modification system such as system 100, 300, 400 or 600. Reference is now made to Fig. 10, which is a simplified schematic diagram of a laser amplifying system including a seed laser failure protection system constructed and operative in accordance with a preferred embodiment of the present invention. As seen in Fig. 10, there is provided a laser system 1000 preferably including a seed laser 1002 providing a first laser output 1003 and an amplifying subsystem, here embodied by way of example as a power amplifier 1004, receiving the first laser output 1003 from seed laser 1002 and amplifying the laser output to provide an amplified laser output 1006. Laser system 1000 may be embodied, by way of example, a Master Oscillator Power Amplifier (MOPA) laser or may be any other laser system including a seed laser and power amplifier. Particularly preferably, laser system 1000 may be incorporated in an OPA laser system of the any of the types described hereinabove with reference to Figs. 1 – 9. As is well known by those skilled in the art, defects in the laser output by seed laser 1002 may result in damage to power amplifier 1004. Typical defects in the laser output by seed laser 1002 causing damage to power amplifier 1004 may include reduction of power of the seed laser output and degradation of the laser line width. Such damage to the power amplifier may occur extremely rapidly, on the order of several nanoseconds, and before the response time of internal sensing mechanisms that may be included in power amplifier 1004. In order to detect such possible defects in the laser output of seed laser 1002, system 1000 further preferably includes a detector subsystem 1020 receiving the output from seed laser 1002. Detector subsystem 1020 may include one or more sensors for sensing properties of the laser output and, more specifically, for detecting possible faults in the laser output. Detector subsystem 1020 is preferably operatively coupled to power amplifier 1004. Detector subsystem 1020 is preferably configured to deactivate power amplifier 1004 upon detection of faults in the laser output from seed laser 1002. It is a particular feature of a preferred embodiment of the present invention that laser system 1000 preferably includes an auxiliary laser subsystem, here preferably embodied as an auxiliary seed laser 1030. Auxiliary seed laser 1030 preferably provides a second laser output 1032 to amplifier 1004, which second laser output 1032 is preferably of a significantly lower power than a power of first laser output 1003. By way of example only, first laser output 1003 may have a first power in the range of 80-100 milliwatts whereas second laser output 1032 may have a second power in the range of 50 – 70 milliwatts. Auxiliary seed laser 1030 preferably provides second laser output 1032 at least upon cessation of seed laser 1002 providing first laser output 1003 to amplifier 1004. Particularly preferably, auxiliary seed laser 1030 preferably operates continuously so as to provide second laser output 1032 to amplifier 1004 both concurrently with seed laser 1002 providing first laser output 1003 thereto as well as upon cessation of seed laser 1002 providing first laser output 1003. During proper operation of seed laser 1002, amplifier 1004 preferably receives both first laser output 1003 from seed laser 1002 and second laser output 10from auxiliary seed laser 1030. Due to the power of second laser output 1032 being significantly lower than the power of first laser output 1003, the contribution of second laser output 1003 to amplified laser output 1006 is preferably negligible. Preferably, although not necessarily, second laser output 1032 is of a different wavelength than first laser output 1003, in order for further reduce the influence of second laser output 10on amplified laser output 1006. By way of example only, first laser output 1003 may have a first wavelength in the range of 1060-1070 nm whereas second laser output 1032 may have a second wavelength in the range of 1070-1080 nm. Upon cessation of laser output from seed laser 1002, due to faulty operation of seed laser 1002 as sensed by detector subsystem 1020, detector subsystem 1020 is preferably operative to deactivate amplifier 1004. Due to the finite response time of amplifier 1004 and detector subsystem 1020, amplifier 1004 is not instantaneously deactivated but rather continues to operate for a finite period of time following cessation of laser output from seed laser 1002. It is understood that during this time, amplifier 1004 no longer receives first laser output 1003 from seed laser 1002. However, auxiliary seed laser 1030 preferably continues to provide second laser output 1032 to amplifier 1004. It is understood that amplifier 1004 thus continues to receive an input signal in the form of second laser output 1032, even in the case that seed laser 1002 has ceased to provide a laser output. The second laser output 1032 provided by auxiliary seed laser 1030 to amplifier 1004 is sufficient to prevent damage to amplifier 1004, which damage would otherwise be likely to occur due to cessation of the provision of a signal thereto, prior to amplifier 1004 being deactivated by sensor 1020. Reference is now made to Fig. 11, which is a simplified schematic diagram of a laser amplifying system including a seed laser failure protection system constructed and operative in accordance with another preferred embodiment of the present invention. As seen in Fig. 11, there is provided a laser system 1100 preferably including a seed laser 1102 providing a first laser output 1103 and an amplifying subsystem, here embodied by way of example as a power amplifier 1104, receiving the first laser output 1103 from seed laser 1102 and amplifying the laser output to provide an amplified laser output 1106. Laser system 1100 may be embodied, by way of example, a Master Oscillator Power Amplifier (MOPA) laser or may be any other laser system including a seed laser and power amplifier. Particularly preferably, laser system 1100 may be incorporated in an OPA laser system of the any of the types described hereinabove with reference to Figs. 1 – 9. As is well known by those skilled in the art, and as described hereinabove, defects in the laser output by seed laser 1102 may result in damage to power amplifier 1104. Typical defects in the laser output by seed laser 1102 causing damage to power amplifier 1104 may include reduction of power of the seed laser output and degradation of the laser line width. Such damage to the power amplifier may occur extremely rapidly, on the order of several nanoseconds, and before the response time of internal sensing mechanisms that may be included in power amplifier 1104. In order to detect such possible defects in the laser output of seed laser 1102, system 1100 further preferably includes a detector subsystem 1120 receiving the output from seed laser 1102. Detector subsystem 1120 may include one or more sensors for sensing properties of the laser output and, more specifically, for detecting possible faults in the laser output. Detector subsystem 1120 is preferably operatively coupled to power amplifier 1104. Detector subsystem 1120 is preferably configured to deactivate power amplifier 1104 upon detection of faults in the laser output from seed laser 1102. It is a particular feature of a preferred embodiment of the present invention that laser system 1100 preferably includes a pair of gratings 1130. Pair of gratings 1130 preferably includes a first reflection grating 1132 preferably positioned at an entry 1134 of amplifier 1104 and a second reflection grating 1136 preferably positioned at an exit 1138 of amplifier 1104. Pair of gratings 1130 in combination with amplifier 1104 preferably form a preferred embodiment of an auxiliary laser subsystem 1140. During proper operation of seed laser 1102, amplifier 1104 preferably receives first laser output 1103 from seed laser 1102 and amplifies first laser output 1103 to provide amplified laser output 1106. Upon cessation of laser output from seed laser 1102, due to faulty operation of seed laser 1102 as sensed by detector subsystem 1120, detector subsystem 1120 is preferably operative to deactivate amplifier 1104. Due to the finite response time of amplifier 1104 and detector subsystem 1120, amplifier 1104 is not instantaneously deactivated but rather typically continues to operate for a finite period of time following cessation of laser output from seed laser 1102. It is understood that during this time, amplifier 1104 no longer receives a laser output from seed laser 1102. In this case, reflection gratings 1130 preferably provide a signal feedback to amplifier 1104, such that amplifier 1104 in combination with pair of gratings 11preferably begins to operate as a laser. Reflection gratings 1130 preferably have a relatively low reflectance such that the signal feedback provided by reflection gratings 1130 is of lower power than the power of the laser output 1103 of seed laser 1102. Particularly preferably, although not necessarily, pair of gratings 11are reflective at a wavelength different than the wavelength of the first laser output 11of seed laser 1102, such that during proper operation of seed laser 1102 gratings 11have negligible influence on amplified output 1106. By way of example only, first laser output 1103 may have a wavelength in the range of 1060-1070 nm whereas gratings 1130 may be reflective at a wavelength in the range of 1090-1100 nm.

It is understood that amplifier 1104 thus continues to receive an input signal in the form of signal feedback from gratings 1130, even in the case that seed laser 1102 has ceased to provide a laser output. As a result, amplifier 1104 in combination with gratings 1130 begins to operate as a laser upon cessation of operation of seed laser 1102, thereby preventing damage to amplifier 1104, which damage would otherwise be likely to occur due to cessation of the provision of a signal thereto. As seen in Figs. 10 and 11, laser output from seed lasers 1002, 1102 may be fed directly to amplifier 1004, 1104 respectively. Alternatively, as illustrated in Figs. and 13, additional elements may be inserted interfacing the seed laser and amplifier. Particularly, a line width filter 1200 may be inserted between seed laser 1002, 1102 and amplifier 1004, 1104 respectively in order to filter out laser beams of unacceptably narrow line width and thus prevent such laser beams from reaching and damaging amplifier 1004, 1104. A particularly preferred embodiment of line width filter 1200 is illustrated in Fig. 14. Turning now to Fig. 14, filter structure 1200 is seen to be implemented downstream of seed laser 1002, 1102 and upstream of amplifier 1004, 1104. It is appreciated that other components of each of systems 1000, 1100 are not shown in Fig. 14 for the sake of clarity. It is further appreciated that the particular structure of filter 1200 is not limited to inclusion in systems 1000, 1100 and rather may be useful in any laser system, for filtering the laser output of a seed laser. The laser output from seed laser 1002, 1102 is preferably split into two parts at a splitter 1405 and recombined at a recombiner 1406. A first part of the split laser output from seed laser 1002, 1102 preferably travels along a first arm 14between splitter 1405 and recombiner 1406. A second part of the split laser output from seed laser 1002, 1102 preferably travels along a second arm 1408 between splitter 1405 and recombiner 1406. As appreciated from a comparison of first and second arms 14and 1408, first arm 1407 preferably includes an additional portion 1409 in comparison to second arm 1408 and thus is longer than second arm 1408. In the case that the laser output from seed laser 1002, 1102 is of unacceptably narrow line width, the laser outputs from first and second arms 1407 and 1408, when recombined at recombiner 1406, will mutually interfere due to the relatively high coherence thereof. The recombined beam is preferably detected by detector 1410, which detector 1410 is preferably connected to an electronic control module 1411. Electronic control module 1411 is preferably a coherent beam combining (CBC) card, in operative control of a phase modulator 1412 located along second arm 1408. Phase modulator 1412 is preferably operated by electronic control card 1411 to alter a phase of the beam along second arm 1408, such that substantially all of the recombined beam at recombiner 1406 is directed towards detector 1410. The recombined beam thus does not proceed towards amplifier 1004, 1104 and hence does not reach and cause damage thereto. The receipt of a laser output from seed laser 1002, 1102 by amplifier 1004, 1104 is thereby halted and a protective compensating signal is delivered to amplifier 1004, 1104 prior to amplifier 1004, 1104 being deactivated. Such a protective compensating signal may be provided by an auxiliary laser subsystem, as detailed hereinabove with respect to Fig. 10, or by way of the initiation of laser operation by the amplifier itself in combination with reflective gratings located at entry and exit ports thereof, as detailed hereinabove with reference to Fig. 11. In the case that seed laser 1002, 1102 is operating properly and the laser output from seed laser 1002, 1102 is of acceptably wide line width, the laser outputs from first and second arms 1407 and 1408, when recombined at recombiner 1406, will not mutually interfere. This is because the line width is sufficiently wide such that the coherence is relatively low and therefore no mutual interference occurs. In this case, a part of the laser output at recombiner 1406 will continue towards amplifier 1004, 1104 and a part of the laser output at recombiner 1406 will be delivered to detector 1410. As described hereinabove, each of the laser systems illustrated herein preferably includes a detector subsystem, such as detector subsystem 1020 or 1120. Detector subsystem 1020 or 1120 is preferably embodied as a sensor for sensing the output from a seed laser, such as seed laser 1002 or 1102. A particularly preferred embodiment of a sensor forming detector subsystem 1020 or 1120 is illustrated in Fig. 15. It is appreciated, however, that the sensor illustrated in Fig. 15 is not limited to use in system 1000 or 1100 and may be incorporated as a laser output sensor in any system benefitting from the use thereof. As seen in Fig. 15, there is provided a detector subsystem 1520. Laser output from a seed laser such as seed laser 1002 or 1102 preferably enters detector subsystem 1520 at an input point 1530 and travels towards a splitter 1534. At splitter 1534, a small portion such as 1% of the laser output is directed towards a detector 15and the remaining portion of the laser output continues towards an amplifier 1540. Amplifier 1540 is preferably a lower power amplifier than power amplifier 1004 or 1104. Amplifier 1540 preferably outputs an amplified laser output, which amplified laser output is preferably delivered to an additional detector 1542 by way of an elongate optical fiber 1544. In operation of detector subsystem 1520, in the case that the output from seed laser 1002 or 1102 ceases, the intensity of the amplified laser output detected at additional detector 1542 decreases. In this case, a control module (not shown) connected to detector 1542 as well as to power amplifier 1004 or 1104 may deactivate power amplifier 1004 or 1104 in order to prevent damage thereto. In the case that the output from seed laser 1002 or 1102 degrades so as to have an unacceptably narrow line width, non-linear effects will be initiated in fiber 1544. It is appreciated that fiber 1544 is advantageously configured so as to be as sensitive as possible to such non-linear effects. For this purpose, fiber 1544 is preferably of considerable length and preferably has a small core diameter, in order to increase the sensitivity of fiber 1544 to the line width of the laser output from the seed laser 1002 or 1102. By way of example only, fiber 1544 may have a length of approximately 25 m and a core diameter of approximately 6 microns. Due to the non-linear effects initiated in fiber 1544 upon narrowing of the line width of the output from seed laser 1002 or 1102, fiber 1544 preferably begins to operate as a mirror, reflecting light backwards towards amplifier 1540. As a result of the reflected light returning to amplifier 1540, an increased signal reaches splitter 15and is detected by an additional detector 1538. Upon detection of an increased signal at detector 1538, power amplifier 1004, 1104 is preferably deactivated in order to prevent damage thereto. It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly claimed hereinbelow. Rather, the scope of the invention includes various combinations and subcombinations of the features described hereinabove as well as modifications and variations thereof as would occur to persons skilled in the art upon reading the forgoing description with reference to the drawings and which are not in the prior art.

Claims

1./ AMENDED CLAIMS 1. A laser system comprising: a seed laser; a laser beam splitting and combining subsystem receiving an output from said seed laser, splitting said output into a plurality of sub-beams and providing a combined laser output comprising said plurality of sub-beams; and a phase modulation subsystem grouping at least a portion of ones of said plurality of sub-beams into a multiplicity of groups of sub-beams, said phase modulation subsystem: in parallel across said multiplicity of groups of sub-beams, varying a phase of each sub-beam within each group relative to phases of other sub-beams within said group so as to vary a phase of each group, and varying said phase of each group relative to phases of other ones of said multiplicity of groups, thereby varying a phase of said combined laser output to provide spatial modulation of said combined laser output.

2. A laser system according to claim 1, wherein said phase modulation subsystem comprises at least one cylindrical lens for performing said grouping.

3. A laser system according to claim 1, wherein said phase modulation subsystem comprises an array of mirrors and corresponding focusing lenses for performing said grouping.

4. A laser system according to any of the preceding claims, wherein said phase modulation subsystem comprises a plurality of phase modulators for varying said phases of said sub-beams.

5. A laser system according to claim 4, wherein said phase modulation subsystem comprises at least one electronic control module in operative control of said plurality of phase modulators. CLAIMS 289719/

6. A laser system according to any of the preceding claims, and wherein said phase modulation subsystem comprises a multiplicity of detectors corresponding to said multiplicity of groups, for detecting a far field intensity pattern of each of said multiplicity of groups.

7. A laser system according to claim 6, wherein said multiplicity of detectors performs said detecting at least partially mutually simultaneously.

8. A laser system according to claim 6 or claim 7, and wherein said phase modulation subsystem comprises an additional auxiliary detector for detecting a combined far field intensity pattern of said multiplicity of groups.

9. A laser system according to claim 4, and wherein said phase modulation subsystem comprises a multiplicity of additional phase modulators, each additional phase modulator being common to all sub-beams within each said group for varying said phase of each group relative to phases of other ones of said multiplicity of groups.

10. A laser system according to claim 9, wherein said phase modulation subsystem comprises an additional electronic control module in operative control of said multiplicity of additional phase modulators.

11. A laser system according to any of the preceding claims, wherein said varying of said phase of said combined laser output comprises maximizing an intensity of said combined laser output.

12. A laser system according to any of the preceding claims, wherein said varying of said phase of said combined laser output provides said spatial modulation of said combined laser output, without involving mechanical spatial modulation of said combined laser output. 289719/

13. A laser system according to any of the preceding claims and wherein said laser beam splitting and combining subsystem provides laser beam amplification downstream of said splitting and upstream of said combining.

14. A method for performing phase variation of a laser output comprising: receiving a laser output from a seed laser; splitting said laser output into a plurality of sub-beams and combining said plurality of sub-beams to provide a combined laser output; grouping at least a portion of ones of said plurality of sub-beams into a multiplicity of groups of sub-beams; in parallel across said multiplicity of groups of sub-beams, varying a phase of each sub-beam within each group relative to phases of other sub-beams within said group so as to vary a phase of each group; and varying said phase of each group relative to phases of other ones of said multiplicity of groups, thereby varying a phase of said combined laser output to provide spatial modulation of said combined laser output.

15. A method according to claim 14, wherein said grouping is performed by at least one cylindrical lens.

16. A method according to claim 14, wherein said grouping is performed by an array of mirrors and corresponding focusing lenses.

17. A method according to any of claims 14 - 16, wherein said varying of said phases of said sub-beams is performed by a plurality of phase modulators.

18. A method according to claim 17, and also comprising controlling said plurality of phase modulators by at least one electronic control module.

19. A method according to any of claims 14 - 18, and also comprising detecting a far field intensity pattern of each of said multiplicity of groups, by a corresponding multiplicity of detectors. 289719/

20. A method according to claim 19, wherein said detecting is performed at least partially mutually simultaneously for said multiplicity of groups.

21. A method according to claim 19 or claim 20, and also comprising detecting a combined far field intensity pattern of said multiplicity of groups, by an auxiliary detector.

22. A method according to claim 17, and wherein said varying of said phase of each group relative to phases of other ones of said multiplicity of groups is performed by a multiplicity of additional phase modulators, each additional phase modulator being common to all sub-beams within each said group.

23. A method according to claim 22, and also comprising controlling said multiplicity of additional phase modulators by an additional electronic control module.

24. A method according to any of claims 14 - 23, wherein said varying of said phase of said combined laser output comprises maximizing an intensity of said combined laser output.

25. A method according to any of claims 14 - 24, wherein said varying of said phase of said combined laser output provides said spatial modulation of said combined laser output, without involving mechanical spatial modulation of said combined laser output.

26. A method according to any of claims 14 – 25, and also comprising amplifying said laser output downstream of said splitting and upstream of said combining.