WO2009118728A1

WO2009118728A1 - A laser aiming and marking device

Info

Publication number: WO2009118728A1
Application number: PCT/IL2009/000325
Authority: WO
Inventors: Gil Tidhar; Ori Aphek; Tal Goichman
Original assignee: Elta Systems Ltd.; Optigo Systems Ltd.
Priority date: 2008-03-25
Filing date: 2009-03-23
Publication date: 2009-10-01
Also published as: IL190419A0

Abstract

Some embodiments of the present invention relate to a system for providing a laser beam. According to some embodiments of the invention a system for providing a laser beam may include at least one semiconductor laser unit (20, 22), a cooling unit and a control unit (40). The at least one semiconductor laser unit (20, 22) is adapted to produce laser energy having a wavelength longer than 3 m and that is detectable by a thermal imaging unit. The cooling unit (80) is adapted to cool at least the semiconductor laser unit(s). The control unit (40) is adapted for activating the cooling unit in conjunction with or around activation of the semiconductor laser unit(s), such that the cooling unit (80) is kept substantially inactive while the semiconductor laser (s) is/are inactive.

Description

A LASER AIMING AND MARKING DEVICE

FIELD OF THE INVENTION

[001] The present invention is in the field of laser aiming and marking.

BACKGROUND OF THE INVENTION

[002] It is known to use electromagnetic energy, such as light (visible and non-visible, including laser energy), to aim or point a device that is associated with an electromagnetic energy source at a distant target. This type of marking is referred to herein as "stand-off marking". It is also known to use electromagnetic energy, such as light (visible and non-visible), to mark a position of an object that is associated with such an electromagnetic energy source. This type of marking is referred to herein as "self marking".

[003] Current portable marking devices typically operate within the Near Infrared (NIR) spectral range or within the visible light spectral range. The NIR marking is viewable through Night Vision Goggles (NVG) and image intensifiers at night. The visible light marking can be seen with the naked eye. Both marking techniques are practical only at nighttime, because during daytime there is strong background radiation due to sun reflections, and the radiation produced by the marking device is practically unnoticeable during daytime. Additionally, both techniques are not compatible with thermal imaging units (TIUs). The only known application of marking in the thermal spectral range (that is compatible with TIUs) involves the use of blackbody radiation from hot filaments and plates. This implementation is inherently limited in many respects.

[004] Thus, current marking devices, and especially portable marking devices are not adequately compatible with thermal imaging technology and equipment and may suffer from significant limitations. Thermal Imaging Units (TIU) generate a video image of a scene which represents a two dimensional gray-body radiation picture of the objects within the scene. TIUs are sensitive to thermal infrared spectral range (where objects at typical outdoor temperatures and above emit significant gray-body radiation). Typically, TIUs work in one of two atmospheric windows within the thermal infrared: the first being between the 3-5μm wavelength band (also referred to as MidWave Infrared, or MWIR), and the second being between the 8-12μm wavelength band (also referred to as Long Wave Infrared, or LWIR). Modern TIUs utilize a two dimensional Focal Plane Array (FPA), although TIUs based on lower dimension arrays in conjunction with scanning mirrors still exist. The higher-end FPAs are cryogenically cooled, and work mostly in MWIR. The affordable technology is based on uncooled FPAs, mostly in the LWIR. Due to the continuing decline in cost and size of TIUs (and especially the uncooled devices), they are becoming increasingly common in the battlefield and elsewhere, replacing some of the lower-end technologies such as Night Vision Goggles (NVGs), which are based on image intensifiers in the visible and NIR spectral range.

[005] Any attempt at designing portable marking devices which operate at the thermal infrared spectral range must overcome significant obstacles which have thus far hindered the introduction of such operable, and functionally capable devices. A major obstacle which has stood in the way of markers in the thermal spectral range is the need to find a solution which provides an acceptable balance between (among others): the portability of the device and its size, the device's power consumption characteristics and the device's performance and versatility.

[006] US Patent No. 4,026,054 to Snyder discloses a laser aiming system for attachment to a conventional firearm such as a pistol, rifle or shotgun. The system disclosed by Snyder utilizes a laser to project a beam of a coherent light onto a target at a given range to indicate the impact point of a projectile fired from a weapon. The laser aiming system includes a laser tube, a self-contained power supply module and apparatus for mounting the laser to the weapon whereby the recoil force developed during firing of the weapon will not be injurious to the laser. The mounting apparatus includes a track fixed relative to the firearm with a carriage that is slidable thereon to provide limited longitudinal reciprocating movement of the laser relative to the weapon. A pneumatic device is operably disposed between the carriage and the weapon to absorb and dissipate the energy of recoil. Compression springs are provided and disposed on opposite sides of the carriage to yieldably resist longitudinal movement of the carriage and return it to an intermediate position on the track after recoil. An attachment mechanism releasably secures the mounting apparatus to the weapon.

[007] US Patent No. 4,233,770 to de Filippis, et al. discloses a laser that is attached to a weapon and its beam is aimed toward the target. The dot of laser light on the target is observed through a light filter which permits passage of light of the same wavelength as the laser light. The filter may also be removed from the line of sight to the target.

[008] US Patent No. 4,771,431 to Nakazawa, et al. discloses a semiconductor laser driver that is designed to detect a semiconductor laser output and control a drive voltage or current of a semiconductor laser so as to set a detected laser output to be a predetermined constant laser output. The laser driver includes an integrator for integrating the detected laser output, thereby utilizing an integrated signal as a semiconductor laser drive signal. The integrator integrates the difference between a voltage corresponding to the detected laser output and a reference voltage corresponding to the predetermined constant laser output.

[009] US Patent No. 4,817,098 to Horikawa discloses a control circuit for applying light quantity and temperature settings to a semiconductor laser controller and a temperature controller, respectively. A temperature actuator is controlled by the temperature controller responsive to an output signal from a temperature sensor for equalizing the temperature of a semiconductor laser to the temperature setting. The semiconductor laser is controlled by the semiconductor laser controller responsive to an output signal from a light quantity sensor so that a laser beam will be emitted from the semiconductor laser at the light quantity setting. Mode hopping noise is detected by a mode hopping noise detector or the control circuit in combination with a memory which stores mode hopping noise ranges. In response to a mode hopping noise signal, the control circuit changes at least one of the light quantity and temperature settings.

[010] US Patent No. 5,043,992 to discloses a laser driver which includes a reference circuit, which may be a bandgap reference, mounted in thermal contact with the laser. The reference produces a current component I_ptat that is proportional to the absolute temperature. The modulation current is proportional to I_ptat, which increases slowly with temperature, up to a certain junction temperature (e.g., 65 to 70 degrees C). Above that -A-

temperature, the modulation current increases more rapidly by adding an additional current component I_COmp- This provides for the required increase in modulation current to compensate for temperature variations in the laser output. This technique allows the laser to be operated without cooling (as by a thermoelectric cooler) in many applications. The laser driver may optionally include circuitry to provide a bias current, which may be controlled by a backface monitor or threshold detector.

[011] US Patent No. 5,738,595 to Carney discloses adapters removably affixing a hand held laser pointer to selected apparatus. The adapters include a structure for mounting therein the laser pointer having a laser module emitting a laser beam, a casing, a voltage source and a switch for controlling the laser module. Also included is a device for maintaining the laser pointer in an 'on' condition and means for removably affixing the adapters to the selected apparatus such that when the adapters are affixed thereon, the laser beam emitted from the laser pointer is aimed in a predetermined relation with respect to the selected apparatus. The laser pointer and associated adapters are employed to optimize the use of the laser pointer and enhance the selected apparatus upon which it is mounted.

[012] US Patent No. 6,307,871 to Heberle discloses a passively cooled solid-state laser system for producing high-output power. The system of Heberle includes an optics bench assembly containing a laser head assembly which generates a high-power laser beam. A laser medium heat sink assembly is positioned in thermal communication with the laser medium for conductively dissipating waste heat and controlling the temperature of the laser medium. A diode array heat sink assembly is positioned in thermal communication with the laser diode array assembly for conductively dissipating waste heat and controlling the temperature of the laser diode array assembly. The heat sink assemblies include heat exchangers with extending surfaces in intimate contact with phase change material. When the laser system is operating, the phase change material changes from solid to liquid phase. This transition of the phase change material also provides a thermal buffer for laser components such that the phase change material absorbs the energy associated with fluctuations in ambient temperature before transferring it to the laser component. Also, the heat sink assembly can contain more than one type of phase change material, each having a different melting temperature. SUMMARY OF THE INVENTION

[013] According to an embodiment of the invention, there is provided a system for providing a laser beam. According to some embodiments a system for providing a laser beam include at least one semiconductor laser unit, a cooling unit and a control unit. The least one semiconductor laser unit adapted to produce laser energy having a wavelength longer than 3μm and that is detectable by a thermal imaging unit. The cooling unit adapted to cool at least the semiconductor laser unit. The control unit adapted for activating the cooling unit in conjunction with or around activation of the semiconductor laser unit, such that the cooling unit is kept substantially inactive while the semiconductor laser is inactive.

[014] In further embodiments, the system further includes a portable electricity source configured and operable for powering components of the system. In yet further embodiments, the control unit is adapted to determine drive parameters for controlling the operation of the semiconductor laser unit based at least on a temperature related input that is associated directly or indirectly with the temperature of the semiconductor laser unit. In still further embodiments, the control unit is adapted to dynamically adapt the drive parameters for controlling the operation of the semiconductor laser unit based on a wavelength of the laser energy produced by the semiconductor laser unit. In still further embodiments, the control unit is adapted to dynamically adapt the drive parameters for controlling the operation of the semiconductor laser unit based on a light power parameter related to the laser energy produced by the semiconductor laser unit. In yet further embodiments, the control unit is adapted to dynamically adapt the drive parameters further based on a thermal damage parameter related to at least one component of the system.

[015] In some embodiments, the control unit is adapted to determine drive parameters which are effective for adapting any one of the following: an input current that is used to power the semiconductor laser unit; a pulse repetition rate at which the semiconductor laser unit is operated; and a duty cycle at which said semiconductor laser unit is operated. [016] In further embodiments, upon receiving an instruction to activate said semiconductor laser unit, the control unit is adapted to determine whether the temperature of the semiconductor laser unit is above an initial temperature threshold, and if the temperature is above the threshold, the control unit is adapted to delay the activation of the laser unit until its temperature drops below the initial threshold. In yet further embodiments, the control unit is adapted to turn-off said cooling unit at or around the time the semiconductor laser unit is turaed-off.

[017] In still further embodiments, the control unit is adapted to optimize the system's laser beam output power or the system's power-to-light efficiency based at least on a temperature related input that is associated directly or indirectly with the temperature of the semiconductor laser unit.

[018] In some embodiments, the semiconductor laser unit is adapted to produce a beam of laser energy at least within a first and a second wavelength band, the first wavelength band being between approximately 3μm-5μm and the second wavelength band being between approximately 8μm-12μm. In further embodiments, the at least one semiconductor laser unit comprises at least a first and a second semiconductor laser unit, said first semiconductor is adapted to produce a beam of laser energy within said first wavelength band and the second semiconductor laser unit is adapted to produce a beam of laser energy within the second wavelength band.

[019] According to yet further embodiments, the at least one semiconductor unit comprises a semiconductor laser unit which is adapted to produce a beam of laser energy at least within the first and the second wavelength bands simultaneously. [020] In some embodiments, the at least one semiconductor laser unit comprises one or more one of the following laser technologies: Lead Salt lasers diodes, Antimonide lasers, Quantum Cascade Lasers (QCL) and Interband Cascade lasers (ICL). [021] In some embodiments, the cooling unit is a thermo electric cooler (TEC). In further embodiments, the cooling unit comprises: a phase changing material (PCM) reservoir that is substantially filled with PCM, and a heat pump having a cold side that is thermally coupled to the semiconductor laser module and a hot side that is thermally coupled to the phase changing material (PCM) reservoir. According to still further embodiments, the PCM is characterized by a melting temperature that is above typical ambient temperatures, and wherein the heat pump is operated so that the operating temperature of the hot side of the heat pump is above the melting temperature of the

PCM. In some embodiments, the PCM reservoir is removable and replaceable.

[022] In some embodiments, the control unit is adapted to implement in respect of a laser beam output of the system a modulation scheme, and the modulation scheme is based on an enhanced sensitivity of the human eye to changes in a scene. In further embodiments, the modulation is effective for controlling the laser beam output so that, within a frequency range that is between 0.0 IHz — 10,000Hz, a substantial portion of the energy of the laser beam output is in a frequency band between 0.1-100Hz.

[023] In some embodiments, a total throughput of the system is in the order of tens to hundreds of milliwatts, and wherein a total power consumption of said system beam is in the order of a few watts up to a few tens of watts.

[024]

[025] According to a further aspect of the invention, there is further provided a system for providing a laser beam which comprises at least one semiconductor laser unit and a control unit. The at least one semiconductor laser unit is adapted to produce laser energy having a wavelength longer than 3μm and that is detectable by a thermal imaging unit.

The control unit for dynamically adapting the drive parameters controlling the operation of the semiconductor laser unit based at least on a temperature related input that is associated directly or indirectly with the temperature of the semiconductor laser unit.

[026] In some embodiments the system further comprises a portable electricity source configured and operable for powering components of the system.

[027] In yet further embodiments, the control unit is adapted to optimize the system's laser beam output power or the system's power-to-light efficiency based at least on the temperature related input.

[028] In some embodiments, upon receiving an instruction to activate the semiconductor laser unit, said control unit is adapted to determine whether the temperature of the semiconductor laser unit is above an initial temperature threshold, and if the temperature is above the threshold, the control unit is adapted to delay the activation of the laser unit until its temperature drops below the initial threshold. [029] In some embodiments, the control unit is adapted to dynamically adapt the drive parameters further based on a thermal damage parameter related to at least one component of the system.

[030] In some embodiments, the semiconductor laser unit is adapted to produce a beam of laser energy at least within a first and a second wavelength band, the first wavelength band being between approximately 3μm-5μm and the second wavelength band being between approximately 8μm-12μm.

[031] In further embodiments, the system the cooling unit comprises a phase changing material (PCM) reservoir and a heat pump. The phase changing material (PCM) reservoir that is substantially filled with PCM. The heat pump having a cold side that is thermally coupled to said semiconductor laser module and a hot side that is thermally coupled to said phase changing material (PCM) reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

[032] In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[033] FIG. 1 is a block diagram illustration of a system for providing a laser beam, according to some embodiments of the invention;

[034] FIG. 2A is a schematic diagram of atmospheric transmittance as a function of wavelength;

[035] FIG. 2B is a schematic diagram of blackbody radiation as a function of wavelength, for black-bodies at different temperatures;

[036] FIG. 3 is a block diagram illustration of system for providing a laser beam which includes a control unit that is adapted to control at least a laser unit within the laser system based on a parameter that is related to a temperature of the laser unit and/or based on a parameter that is related to an output light power parameter that is related to the output of the laser system, according to some embodiments of the invention;

[037] FIG. 4A is a graph illustrating the light power dependence of a typical QCL laser on input current, for different laser temperature settings;

[038] FIG. 4B is a graph illustrating the drive parameters dependence on temperature of a typical QCL laser;

[039] FIG. 5 is a flowchart illustration of a method of managing a laser unit's drive parameters, according to some embodiments of the invention;

[040] FIG. 6A is an illustration of a possible modulation scheme in a constant frequency, at which the system according to some embodiments of the invention may be operated, and of a respective frequency power distribution;

[041 ] FIG. 6B is a schematic illustration of the sensitivity of the human eye to flicker;

[042] FIG. 7 is a block diagram illustration of a system for providing a laser beam comprising at least a first and second semiconductor laser unit(s), the first semiconductor laser unit being configured for producing laser energy which is characterized by a wavelength that is between approximately 3μm-5μm, and the second semiconductor laser unit being configured for producing laser energy which is characterized by a wavelength that is between approximately 8μm-12μm, according to some embodiments of the invention;

[043] FIG. 8 is a block diagram illustration of a system for providing a laser beam comprising a plurality (two or more) of semiconductor laser units, and in association with each one of the plurality of semiconductor laser units the system includes an optical collimating module, according to some embodiments of the invention;

[044] FIG. 9 A is a graphical illustration of the system for providing a laser beam according to some embodiments of the invention, while being used in the stand-off marking mode;

[045] FIG. 9B is a graphical illustration of the system for providing a laser beam according to some embodiments of the invention, while being used in the self-marking mode;

[046] FIG. 10 is a graph showing Spectral Radiance Contrast for different wavelengths;

[047] FIG. 11 is a block diagram illustration of a system for providing a laser beam which includes an optical collimating module that can be selectively positioned in or out- of the optical path of the laser energy output of the semiconductor laser module, according to some embodiments of the invention;

[048] FIG. 12A is a block diagram illustration of a system for providing a laser beam which includes a heat-sink component that is coupled to a phase changing material, according to some embodiments of the invention;

[049] FIG. 12B is an isometric view of the system shown in FIG. 12 A; and

[050] FIG. 13 is a graph schematically illustrating the temperature increase of a typical phase changing material as a function of the amount of thermal energy absorbed by the phase changing material, and specifically the substantially constant temperature during the melting phase.

[051] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE INVENTION

[052] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention 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 invention.

[053] Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as "processing", "computing", "calculating", "determining", "generating", "assigning", "controlling" or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities within the computing system's registers and/or memories into other data similarly represented as physical quantities within the computing system's memories, registers or other such information storage, transmission or display devices.

[054] The processes and displays presented herein are not inherently related to any particular computer or other apparatus. Various general purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct a more specialized apparatus to perform the desired method. The desired structure for a variety of these systems will appear from the description below. In addition, embodiments of the present invention are not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the inventions as described herein.

[055] Throughout the specification and the claims reference is made to the term "thermal imaging unit". The term "thermal imaging unit" or in abbreviation "TIU" as used herein, relates to any thermal imaging device which is configured to detect radiation in the MWIR spectral range and/or in the LWIR spectral range and generates an image based on that radiation. The image produced by the TIU provides a human viewer with a visual representation of the MWIR and/or the LWIR radiation detected by the TIU. It would be appreciated that some thermal imaging units may be operable with additional auxiliary components, and that some embodiments of the present invention may collectively relate to the thermal imaging unit with some auxiliary components as a "thermal imaging unit" or "TIU". It would be further appreciated that some embodiments of the invention are compatible and/or are operable with any such thermal imaging unit, whether presently known or yet to be devised in the future.

[056] Throughout the specification and the claims reference is made to the term "visual sensitivity of the human eye". According to some embodiments of the invention, the term "visual sensitivity of the human eye" as used herein may relate to a visual sensitivity of the human eye when viewing an image processed and displayed by a thermal imaging unit. Furthermore, the term "visual sensitivity of the human eye" may relate to a specific sensitivity parameter or parameters of the human eye and not necessarily to all human vision sensitivity parameters. For example, a system for providing a laser beam according to some embodiments of the present invention may be configured to provide a laser beam output that is compatible with an enhanced human vision sensitivity to flicker. Further by way of example, a system for providing a laser beam according to some embodiments the present invention may be configured to provide a relatively strong laser beam output while substantially maintaining or possibly improving other characteristics of such systems, including but not limited to one or more of the following: portability, size, power consumption, performance, versatility and compatibility with some imaging systems. It would be appreciated that a relatively strong laser beam output may contribute towards a stronger signature being detected by the imaging unit (e.g., a TIU) and that a more contrasting image of the laser marking may be thus achieved.

[057] Throughout the specification and the claims reference is made to the term "a portable energy unit". According to some embodiments of the invention, the term "a portable energy unit" as used herein may relate to any power or energy supply unit(s) which, while being used as a "stand-alone" or a "self-contained" unit, (e.g., while being disconnected from a electricity power grid or some other external abundant energy source,) is able to provide sufficient power for activating components of a respective device for a significant amount of time. Such an energy supply unit may include, for example a rechargeable battery or a disposable (non-rechargeable) battery, as well as other energy storage and discharge units.

[058] Reference is now made to FIG. 1, which is a block diagram illustration of a system for providing a laser beam, according to some embodiments of the invention. According to some embodiments of the invention, a system for providing a laser beam 10 may include a semiconductor laser module 20, a portable energy unit 30, a control unit 40 and a cooling unit 80. The system 10 may further include a collimating module 50. Also shown is an exit window 55, through which the laser beam output of the system 10 can propagate out of the system, and an optional beam combining module 57 which will be discussed in greater detail below.

[059] According to some embodiments of the invention, the system for providing a laser beam 10 may be characterized by weight and size properties which are comparable with typical personal gear of a foot soldier. According to further embodiments of the invention, the system for providing a laser beam 10 may be mountable on the personal gear of an infantry soldier. According to one non-limiting example, the system for providing a laser beam 10 according to some embodiments of the invention may be mountable on a personal weapon of an infantry soldier. According to another non- limiting example, the system for providing a laser beam 10 according to some embodiments of the invention may be handheldable. According to further embodiments of the invention, the system 10 may be characterized by weight and size properties which are comparable with typical vehicle mounted equipment, including vehicles such as, but not limited to, reconnaissance vehicles and tanks.

[060] It should be appreciated that the reference made in the description of some embodiments of the invention to a military use and/or to military personnel equipment is non-limiting, and that further embodiments of the invention contemplate using the system for providing a laser beam 10 discussed herein for other purposes and by non-military personnel and/or while being mounted on non-military equipment or vehicles.

[061] Having discussed in general the system for providing a laser beam 10, there is now provided a description of some the components of the system 10. As mentioned above, the system for providing a laser beam 10 may include a semiconductor laser module 20, a portable energy unit 30, a control unit 40 and a cooling unit 80. The system 10 may further include a collimating module 50. According to some embodiments of the invention, the semiconductor laser module 20 may be adapted to produce at least one beam of laser energy having a wavelength that is longer than 3μm and whose characteristics render it detectable by a thermal imaging unit (not shown in FIG. 1). According to further embodiments of the invention, the semiconductor laser module 20 may be configured to produce the beam(s) of laser energy such that it is visible through the TIU to the human eye.

[062] As would be appreciated by those of ordinary skill in the art, and as will be explained in further detail below, in order for the beam(s) of laser energy generated by the semiconductor laser module 20 detectable by a TIU, and in particular such that it would be visible through a TIU to the human eye, the beam needs to comply with a sensitivity parameter of the TIU. Thus, the system 10 should at least be able to provide a beam of laser energy that is characterized by a wavelength that is within the spectral range that is detectable by a typical TIU. Since typical TIUs operate within defined atmospheric windows, the first being within the Mid Wave IR spectral range (or MWIR), typically between 3μm-5μm, and the second being within the Long Wave IR spectral range (or LWIR), typically between 8μm-12μm, the system 10 should be able to provide a beam of laser energy that is characterized by a wavelength that is at least within one of these atmospheric windows. FIG. 2A, which is a schematic diagram of atmospheric transmittance as a function of wavelength, and to which reference is now made, clearly shows the above referenced atmospheric windows (above 5μm and below 8μm where there is high absorbance by H₂O molecules). Additional reference is made to FIG. 2B, which is a schematic diagram of blackbody radiation as a function of wavelength, for blackbodies at different temperatures. As is illustrated by FIG. 2B, for temperatures typical to ambient outdoor scenes there is a significant blackbody emission within the MWIR and especially within the LWIR spectral range.

[063] It would be further appreciated, that in order for a thermal signature that is displayed by a thermal imaging unit to be noticeable by the human eye, the semiconductor laser module 20 may be required to provide a beam(s) of laser energy whose characteristics render it noticeable or visible through the thermal imaging unit. Such characteristics may include according to one non-limiting example, a certain level of intensity and a certain level of beam divergence. For example, in case that the system 10 is used in standoff-marking mode, the laser radiation reflected from the target to which the laser is aimed needs to be comparable or stronger than the radiation difference between different objects in the scene. Considering a typical thermal radiation contrast, a required range between the system and the target, a given resolution of the TIU and its wavelength, the laser beam divergence and the minimum level of laser intensity may be deduced.

[064] For example, according to some embodiments of the invention, and taking into account typical conditions and operational situations, the semiconductor laser module 20 may be configured to provide sufficient laser energy so as to enable the system 10 to provide a total throughput that is in the order of tens to hundreds of milliwatts. Further by way of example and in accordance with some embodiments of the invention, the proposed system 10 may be configured to provide a total throughput that is in the order of tens to hundreds of milliwatts while maintaining a total power consumption that is in the order of a few watts up to a few tens of watts. Such power levels coupled with a beam divergence of less than one milliradian, in a typical distance between a system and a diffusive target of hundreds to thousands of meters, create a radiation difference which is distinguishable to the human eye when compared to the radiation difference between other objects in the scene which result from temperature or emissivity differences. Divergence of the laser beam output of the system may be adjusted using a collimating module 50. The collimating module is described in further detail below.

[065] As is illustrated by FIG. 2B, for temperatures typical to outdoor scenes, the blackbody emission peaks between 9-1 lμm. The radiation within the 3-5μm is lower by a large factor. Therefore, the laser radiation intensity required to achieve the same signal to clutter radiation at the TIU is much higher for lasers emitting in the LWIR for LWIR TIUs than for lasers emitting in the MWIR for MWIR TIUs (in scenarios which are identical in other respects).

[066] According to some embodiments of the invention, the semiconductor laser module 20 may provide a source of laser energy that is compatible with the size and weight characteristics of the typical personal gear of a foot soldier. According to further embodiments of the invention, the semiconductor laser module 20 may provide a source of laser energy that is compatible with the size and weight characteristics of typical vehicle mounted equipment, including vehicles such as, but not limited to, reconnaissance vehicles and tanks. More details about size and weight characteristics of a semiconductor laser module, which may be used as part of a system for providing a laser beam according to some embodiments of the invention, shall be provided below.

[067] As mentioned above, the system for providing a laser beam 10 may further include an optical collimating module 50. According to some embodiments of the invention, the optical collimating module 50 may be adapted for changing the beam shape or the cross section of the beam(s) of laser energy produced by the semiconductor laser unit 20. According to further embodiments of the invention, the optical collimating module 50 may be adapted to reduce the divergence of the beam(s) of laser energy exiting the semiconductor laser module 20. Thus, it would be appreciated that according to some embodiments of the invention, the optical collimating module 50 may be utilized so as to provide a laser beam(s) output of said system 10 that is characterized by a beam divergence that is substantially smaller than the divergence of the beam(s) of laser energy exiting the semiconductor laser module 20. For example, according to one embodiment of the invention, the optical collimating module 50 may be adapted to provide a laser beam(s) output of said system 10 whose divergence is less than approximately 1 milliradian. According to some embodiments of the invention the collimating module 50 may be used selectively as will be described in greater detail below.

[068] According to some embodiments of the invention, a portable energy unit 30 may also be incorporated into the system 10. The portable energy unit 30 may be configured and operable for providing energy and powering components of the system 10. For example, the portable energy unit 30 may be configured to provide the electric power that is needed to enable the operation of each one of the semiconductor laser module 20 and the control unit 40. As will be discussed in further detail below, the system for providing a laser beam 10 according to some embodiments of the invention, may be designed (e.g., include components) and be adapted to implement configurations which are power efficient, so that the system 10 is able to provide good performance and versatile utility while maintaining substantially low power consumption. It would be appreciated, that a design which combines relatively low power consumption characteristics with functionality and versatility is highly synergetic with a portable utility.

[069] It would be appreciated that a laser system which includes a semiconductor laser unit(s) and which utilizes a semiconductor laser unit to generate a laser energy output that is characterized by a wavelength longer than 3μm and which is expected to provide output power that is in the order of tens to hundreds of milliwatts, would require a cooling unit in order to be able to operate effectively and for a meaningful period of time at ambient temperatures. According to one non-limiting example, the laser should be capable of emitting laser energy for a total duration of several tens of minutes every 24 hours, using a single battery set, and should be ready for operation within few tens of seconds to seconds from receiving an instruction or request or otherwise being activated by a user.

[070] It would be further appreciated that in some laser systems, the laser unit is cooled down to a substantially constant temperature and for relatively long periods of time. Cooling is usually not directly related to the activation of the laser unit. Rather, the laser is continuously kept cooled-down to a certain constant temperature. This cooling regime is intended to achieve substantially constant (and usually best or optimal) output power and substantially constant wavelength, almost instantly upon request. However, in order to maintain the laser unit at a substantially low-temperature (e.g., compared to ambient temperatures) for a substantially long period of time, and not only during or around activation, an abundant energy source is required. Therefore, such systems are typically non-portable. Usually such systems are also not characterized by being required to provide short periods of laser energy within a long period of idle time using a portable energy source.

[071] In a portable unit, where low power consumption is an important design feature, the need to cool the laser unit over long periods of time may be a significant drawback. As will be described in further detail below, according to some embodiments of the invention, a control unit 40 of the proposed system 10 may be adapted to control the activation of the cooling unit 80 so that it is activated during or around the activation of the semiconductor laser unit 22 (this principle is sometimes referred to herein as "transient cooling"). While the semiconductor laser unit 22 is not active, the control unit 40 may keep the cooling unit 80 substantially inactive. It would be appreciated that compared to the steady-state approach, the proposed laser activation-related approach may enable to reduce the average amount of power that is consumed by the laser system 10. Thus, a smaller and lighter energy unit may be used within the proposed system. Furthermore, by implementing this approach it may also be possible to design a laser system 10 which is relatively small in dimensions and which is relatively light, particularly when compared to other laser systems which are intended to provide a laser beam output.

[072] Furthermore, according to some embodiments of the invention, in order to reduce activation lag and to provide substantially optimal output power or power-to-light efficiency, the control unit 40 may be configured to dynamically control the drive parameters of the semiconductor laser unit 22. It would be appreciated, that since according to some embodiments of the invention, the laser system 10 would not be implementing, at least some of the time, the steady-state approach described above, and instead may substantially limit the activation of the cooling unit 80 to about the period of time during which the semiconductor laser unit 22 is activated, when a request to activate the laser (for example, an operator of the system pressing an activation button) is received, a preliminary cooling process may be implemented by the control unit 40 before activating the laser unit 22. The preliminary cooling process may be implemented, for example, in order to bring the laser's temperature below a thermal damage threshold or, in accordance with another example, in order to bring the laser's temperature below a threshold related to a minimal efficiency parameter. According to further embodiments of the invention, either in addition or as an alternative to the above threshold, the preliminary cooling process may be implemented in order to bring the laser's temperature below a threshold related to a minimal output power threshold.

[073] It would be further appreciated, that since according to some embodiments of the invention, the laser system 10 would not be implementing, at least part of the time, the steady-state approach described above, and instead may substantially limit the activation of the cooling unit 80 to the time of the activation of the semiconductor laser unit 22 (or to some time around such activation), the temperature of the laser unit 22 may vary significantly during the activation period of the laser unit 22. For example, according to embodiments of the invention, prior to the request for laser energy, the laser unit's 22 temperature may be substantially equal to the ambient temperature. When a request to activate the laser is received, the control unit 40 may initiate the preliminary cooling process in order to bring the laser's 22 temperature below a minimal output power threshold. Once the laser unit 22 unit is below the minimal output power threshold, the control unit 40 may begin to activate the laser. During the time the laser unit 22 is being activated the temperature of the laser unit 22 may vary. For example, according to some embodiments of the invention and as will be discussed below, initially the temperature of the laser unit 22 may gradually decrease and if the laser unit 22 remains activated for a substantially long period of time its temperature may, at some point, begin to rise gradually.

[074] It should be further noted, that the performance of semiconductor lasers emitting in the MWIR and LWIR spectral range is sensitive to operating temperatures. Generally, the lower the temperature, the better the performance. Moreover, the driving parameters which would extract the maximum optical power or the maximum power-to-light power efficiency, are temperature dependent. Thus, according to some embodiments of the invention, the control unit 40 may be configured to adapt or otherwise control the drive parameters of the semiconductor laser unit 22 based upon information related to the temperature of at least the semiconductor laser unit 22. It would be appreciated that based on information related to a temperature of the semiconductor laser unit 22 and taking into account a thermal damage threshold of at least one component of the laser system 10 the laser unit 22 (e.g. the laser unit), the control unit 40 may be adapted to determine optimal drive parameters for the laser unit 22, as will be described in further detail below. The control unit 40 may be sensitive to thermal damage information which relates to any one of the following: a laser unit(s), a mirror or any other optical element of the system, a casing, a cooling unit, an electronic component used within the system, etc. According to some embodiments of the invention, the optimal drive parameters may be intended to maximize the output power of the system 10 and/or to maximize the power- to-light efficiency of the system 10. [075] The inventors of the present invention propose in accordance with some embodiments of the invention, a system for providing a laser beam 10 which includes a control unit 40 that is configured to limit the activation of the cooling unit 80 to the time of the activation of the semiconductor laser unit 22 (or around that period) while maintaining good functionality. Furthermore, the inventors of the present invention discovered that with efficient optical design, proper configuration of the control unit 40 and an efficient design of the cooling unit 80 (a proposed design for the cooling unit is provided below), the lag time (due to the preliminary cooling) can be kept relatively low and would be acceptable in many cases. Still further, the inventors of the present invention discovered that with efficient optical design, proper configuration of the control unit 40 and an efficient design of the cooling unit 80 (a proposed design for the cooling unit is provided below), the output power of the laser system 10 or its power-to-light efficiency can reach and even exceed performance requirements which represent many real-life scenarios at which the proposed system 10 may be required to operate. As mentioned above by way of example, the performance parameters may be similar to the following: a total throughput that is in the order of tens to hundreds of milliwatts with a total power consumption that is in the order of a few watts up to a few tens of watts. Such power levels coupled with a beam divergence of less than a milliradian, in a typical distance between a system and a diffusive target of hundreds to thousands of meters, are expected to create a radiation difference which is normally distinguishable to the human eye (when viewed over a TIU' s display) compared to the radiation difference between other objects in the scene which result from temperature or emissivity differences. A similar effect may be achieved at the self-marking mode, where the laser beam output diverges over a wide sector, for example, between 5-90 degrees wide, and the TIU is located within that sector at a distance of tens to ten thousands of meters from the system. Furthermore, the system according to the invention may provide such performance without placing a heavy penalty in terms of size or weight of the system.

[076] Having described in some detail certain aspects which are related to the cooling of the system 10 according to some embodiments, the description of further embodiments of the invention continues with a description of further measures which may be implemented by the proposed system 10 in order to improve utility, efficiency and portability and/or other aspects of the system 10.

[077] According to a further aspect of the invention, control unit 40 may be adapted to directly or indirectly control a laser unit 22 based on a temperature related input which is directly or indirectly related to the temperature of the laser unit 22. According to some embodiments, the control unit 40 may be adapted to set or change the drive parameters or the drive signal that are used to control the laser unit's 22 operation based on data relating to the laser unit's 22 temperature. The control unit 40 may determine or estimate, based on the laser unit's 22 temperature, or based on some other information that is related to the laser unit's 22 temperature, which drive parameters would provide a preferred result in terms of laser output power.

[078] Reference is now made to FIG. 3, which is a block diagram illustration of a system for providing a laser beam which includes a control unit that is adapted to control at least a laser unit within the laser system based on a parameter that is related to a temperature of the laser unit and/or based on a parameter that is related to an output light power parameter that is related to the output of the laser system, according to some embodiments of the invention. Various embodiments of the system 10 illustrated in FIG. 3, and a description of the operation of its components is provided below.

[079] According to some embodiments of the invention, the control unit 40 may be adapted to determine drive parameters for the semiconductor laser unit 22 based at least on a temperature related input that is associated directly or indirectly with the temperature of the semiconductor laser unit 22. As is shown in FIG. 3, and according to some embodiments of the invention, the laser control unit 40 may be in communication with a temperature detector 44 that is adapted to measure, for example, the temperature of the semiconductor laser unit 22 (more than one temperature sensor or detector may be used). In accordance with one example, the temperature detector 44 may be thermally coupled to the semiconductor laser unit 22, and thus may be adapted to read the temperature of the semiconductor laser unit 22 (or the temperature of some portion of the semiconductor laser unit 22). The temperature detector 44 may be configured to provide laser temperature indication signals to the laser control unit 40, and based on the laser temperature indication signals from the temperature detector 44 the laser control unit 40 may calculate or otherwise derive a signal indicative of laser drive current level or shape or any other appropriate drive control signal. This process may be carried out continuously so that the data with respect to the temperature of the laser unit 22 is up-to- date. The laser control unit 40 may be adapted to provide drive control signals to a laser driver 42 that is functionally associated with the laser unit 22, and thus the laser control unit 40 may adapt the drive signals which are used to drive the laser unit 22. According to a further embodiment, the laser control unit 40, may generate the drive signals itself and may be used as both the laser driver and the control unit.

[080] Reference is now made to FIG. 4A and to FIG. 4B. FIG. 4A shows the light power dependence of a typical QCL laser on input current, for different laser temperature settings. The maximum power in each temperature is obtained for a different current level. Drawing the current which maximizes light power as a function of temperature yields FIG. 4B, which is an example of drive parameters dependence on temperature of a typical QCL laser for maximizing output power of the QCL laser. Similar methodology may be implemented over a multi-dimensional dependence of power on current, DC and pulse repetition rate (sometime referred to herein as: "PRR") which shall be discussed below. One may also impose constraints such as damage threshold and power efficiency in order to obtain the desired relations between drive parameters and temperature parameters while further taking into account the predefined constraints. A discussion with respect to the relation between damage threshold and power efficiency is also provided below.

[081] According to some embodiments of the invention, when calculating, or otherwise determining the drive parameters, the control unit 40 may take into account one or more thermal damage thresholds. The thermal damage threshold(s) may relate to a certain temperature(s) at which the laser unit 22 and/or other components of the system 10 or components that are associated with the system 10 may begin to sustain damage. In accordance with an embodiment of the invention, the control unit 40 may be configured to search for, or otherwise determine, which drive parameters would provide relatively high laser output power, or relatively high laser power-to-light efficiency (or a parameter derived from a mix of the two), given the temperature related input and the one or more thermal damage inputs. In accordance with a further embodiment, the control unit 40 may be configured to search for drive parameters which are expected to substantially maximize one or more of the output parameters without violating the thermal damage constraint(s). In accordance with one embodiment the control unit 40 may be configured to search for drive parameters which, based at least on a thermal damage threshold of the laser unit 22 (and possibly of the components of the laser system), would substantially optimize laser output power, or laser power-to-light efficiency. It should be appreciated that in addition or as an alternative to the thermal damage constraint(s) discussed hereinabove, other constraints may also be defined and the control unit 40 be configured to search for drive parameters which are expected to substantially maximize output parameters of the system 10 without violating these constraint(s).

[082] The output power of semiconductor lasers emitting photons in the MWIR and LWIR spectral range is related to the laser unit's operating temperature. Thus, in case a semiconductor laser unit 22 is operated under varying temperatures, in order to achieve optimal optical power or best electricity to light-power efficiency, the control unit 40 needs to take into account temperature related parameters when calculating control or drive signals (either independently or in cooperation with a dedicated laser driver unit). Furthermore, in case drive parameters that are optimal for relatively low temperatures are used at high temperatures, the laser power may be significantly reduced, and in some cases, the laser may be irreversibly damaged. This is because high current and/or high duty cycle, which may be optimal for low temperatures, may heat the laser or related components beyond a thermal damage threshold. As a result, a control unit 40 which does not take into account the temperature related data, cannot provide good laser output efficiency at a varying temperatures environment. Furthermore, in order to avoid damage, operating a laser unit at different temperatures may require consideration of and protection against thermal damage due to excess heat.

[083] According to some embodiments of the invention, the control unit 40 may be adapted to generate control signals which are intended to adapt or otherwise influence a duty cycle and/or a pulse repetition rate (abbreviated: "PRR") of the semiconductor laser unit 22 according to variations in the temperature of the laser unit 22 or of some other component that is associated with the laser unit 22. The temperature of such other component(s), e.g. the laser system casing (not shown), may be used as an indication with regard to the temperature of the laser unit 22 and/or it may also be used to indicate the temperature of other components that are part of or which are otherwise associated with the system 10 (and which may also suffer damage due to overheating).

[084] According to a further embodiment of the invention, the control unit 40 may adapt the current level which is used to drive the laser unit according to variations in the temperature of the semiconductor laser unit 22 or of some other component that is associated with the laser unit 22. The control unit 40 may include a laser driver interface (not shown) for facilitating provisioning of drive parameters to a laser driver 42 that is associated with the semiconductor laser unit 22. The drive parameters may be effective for controlling the operation of the laser driver 42 and thus for controlling the operation of the semiconductor laser unit 22.

[085] The temperature and/or other parameters which are related to the laser unit's 22 output may be sampled repeatedly (e.g., at a certain frequency) and the drive signal or the drive parameters may be continuously adjusted as necessary based upon the updated readings. According to still further embodiments of the invention, when the semiconductor laser unit 22 is inactive and possibly also in-between two pulses, the current flow to the semiconductor laser unit 22 may be close to zero. This is an implicit result of the control signal which may be provisioned by the control unit 40. For example, the control unit 40 may issue control signals to the laser driver 42, the laser driver 42 may translate the control signals to drive signals, according to which the semiconductor laser unit 22 would be intermittently activated according to a certain pulse scheme that is related to the control signals provided by the control unit 40. For example, the control unit 40 may adapt the PRR or DC or both of the semiconductor laser unit 22.

[086] In accordance with yet further embodiments of the invention, the temperature related data, and according to a specific example, the temperature of the laser unit 22, may also be inferred by measuring the laser beam output wavelength. There is a known dependency of wavelength on the temperature of the laser unit 22 (particularly, this dependency is known for semiconductor lasers, and specifically in QCL). For example, according to one implementation, the system 10 may further include a light tap 45 and a wavelength analyzer (not shown). The light tap 45 may divert a (typically small) portion of the laser light that has been produced by the system 10 for being analyzed by the wavelength analyzer, which in turn may provide an indication regarding the wavelength of the laser light that is being produced by (and about to be emitted out of) the system 10. This process may be carried out continuously so that the data with respect to the wavelength of the laser light output is up-to-date. The wavelength analyzer may continuously provide laser light wavelength indications to the control unit 40. The control unit 40 may be adapted to calculate or otherwise derive appropriate drive control signals or appropriate drive signals for adapting the operation of the laser unit(s) 22. According to one embodiment of the invention, the control unit 40 may receive information relating to the wavelength of the laser beam output of the system 10 as an indication of the temperature of the laser unit(s) 22. Optionally, the control unit 40 may calculate or evaluate or otherwise determine what is the temperature of the laser unit or units 22 based on the information relating to the wavelength of the laser beam output.

[087] The control unit 40 may be adapted to calculate the optimal current level, and if pulsed mode is used, the optimal PRR and DC is based on the information relating to the wavelength of the laser beam output. For example, the laser management module (or the laser control unit 40) may determine which current level or which PRR and DC would yield the highest output power without risking the laser reliability. According to a further embodiment, the control unit 40 may also take into account the laser unit's 22 or the system's 10 output power or the output power-to-light efficiency. According to some embodiments of the invention, the relation between the inputs (the uncontrolled parameters — temperature, power and wavelength), and the drive parameters (the controlled parameters - e.g. the driver current, the PRR, etc.) may be determined in advance. This relation may be influenced by the damage threshold mechanisms of the laser (maximum temperature at the core, Catastrophic Mirror Damage and other damage mechanisms), and by the dependence of the output power on the input current characteristics, at different temperatures.

[088] According to some embodiments of the invention, in addition to the indication with respect to the laser unit's 22 temperature (whether provided directly or derived from some other input) the control unit 40 may also receive information related to the output light power parameter or some other parameter which is related to the output power of the laser unit 22 or of the laser system 10. For example, according to some embodiments of the invention, the light tap 45 mentioned above, may divert a (typically small) portion of the laser light that has been produced by the system 10 through a light detector (as an example), and the light detector 46 may infer or otherwise determine based on the diverted light some measure related to the laser light power that is produced by the system 10 (at a certain instant). The light detector 46 may generate a laser light power indication signal based on its measurement(s) and may provide the laser light power indication signal to the laser control unit 40. The control unit 40 may then calculate drive control signals or actual drive signals based on the laser light power indication and some light power optimization criterion or formula, in order to adapt the operation of the laser unit(s) 22 so that it becomes optimal. According to further embodiments of the invention, the control unit 40 may use a predefined relationship between the output light power of the laser unit 22 or of the system 10 and the laser unit's 22 temperature or some other parameter which is related to the laser unit's 22 temperature in order to adapt the operation of the laser unit(s) 22 so that it becomes optimal. Thus, for example, given a certain temperature and an actual output light power reading, the control unit 40 may determine drive parameters (or control signals for adapted the drive parameters of the laser unit 22) which would bring the laser unit's 22 output closer to optimal. This process may also continue repeatedly. According to further embodiments of the invention, at least in some cases, optimizing the laser drive parameters may be based upon laser light power indications alone or based on laser light power indications and some other parameter which is not related to the temperature of the laser unit 22. For example, in case damage threshold(s) are associated with higher current level than the current that is needed for achieving maximum power at any given case, optimization of the laser driver parameters may be based on laser light power measurements alone.

[089] Reference is now made to FIG. 5, which is a flowchart illustration of a method of managing a laser unit's drive parameters, according to some embodiments of the invention. According to some embodiments of the invention, an output power light maximization formula may be obtained (block 510). According to other embodiments of the invention, the relation between the temperature of the laser unit (or some other information which is related to the temperature of the laser unit), the output power light of the laser unit or system and the optimal drive parameters may take any other form, and is not necessarily limited to being expressed by a mathematical formula. For example, a look-up table (LUT) may be used to organize the relation, such that given a certain temperature value and a certain output power, light value designated drive parameter may be obtained.

[090] During operation of the laser unit, data related to the temperature of the laser unit and data related to the temperature of the laser unit may be obtained (block 520). According to a further embodiment, output of laser light power may also be measured. As mentioned above, in accordance with some embodiments of the invention, the data related to the temperature of the laser unit may include any data which is indicative of the temperature of the laser unit and is not limited to an explicit reading of the laser unit's temperature. For example, the temperature of the casing of the laser system may be used as the indication with respect to the temperature of the laser unit. In accordance with another example, the wavelength of the output laser beam of the laser system may be used as an indication with respect to the temperature of the laser unit.

[091 ] Based on the maximizing formula (or any other data expressing the temperature to output-power-light relation) and based on the input data, one or more drive parameters may be calculated (block 530) and may be used to adapt the drive parameters of the laser unit (block 535). The control unit or some other laser management module within the laser system may be adapted to repeatedly measure or sample the laser unit's temperature of the laser unit (or some related parameter) (block 540). According to further embodiments, the control unit may be adapted to measure the output light power of the laser system.

[092] It would therefore be appreciated, that using a control unit that is capable of controlling a laser unit based on a temperature related input which is directly or indirectly related to the temperature of the laser unit, can provide significant advantages in terms of portability and utility of the laser system, energetic efficiency or power-to-light efficiency, responsiveness, reliability and more. According to some embodiments of the invention, the control unit may enable to provide initial laser energy output within a relatively short period of time after such laser energy is requested without having to wait for the laser unit to cool down to optimal or otherwise designated operating temperature, and afterwards as the laser unit(s) gradually cools down, the control unit 40 may cause the output power of the laser unit to be increased. According to some embodiments, the control unit 40 may continuously seek to optimize the output power of the laser unit according to its current temperature.

[093] A further aspect of the invention relates to a device for managing operation of a semiconductor laser unit which includes a laser management module and a laser driver interface. According to some embodiments of the invention, the laser management module may be adapted to implement the functionality of the control unit that is part of the laser system. Unless specifically stated or otherwise apparent from the text, any reference made herein to the control unit may be interchanged with a reference to the laser management module that is part of the device for management operation of the semiconductor laser unit. The laser driver interface may be adapted to facilitate provisioning of drive parameters selected or otherwise determined by the laser management module to the laser driver that is associated with the semiconductor laser unit.

[094] As part of its functionality, the laser management module may be adapted, according to some embodiments of the invention, to continuously adjust the drive signal or the drive parameters which control the operation of the laser unit according to the laser unit's temperature. The laser management module may be associated with one or more sensors which may be used to measure temperature that is related to the temperature of the laser unit. The laser management module may take into account information related to the temperature of the laser unit and may adapt the drive signal or the drive parameters which are related to the laser unit according to the present temperature of the laser unit (or some temperature value related to the laser unit). In accordance with some embodiments of the invention, the laser management module may be adapted to optimize the output power of the laser unit per a given operation temperature of the laser unit. Thus, incorporating the proposed laser management module within a laser system may enable the laser system to respond to a request to provide laser energy within a relatively short time, while maintaining good power-to-light efficiency. Specifically, the laser management module may enable to optimize the output of the laser energy according to the dynamically changing temperature of the laser unit. As mentioned above with reference to the control unit of the laser system, the laser management module may be further adapted to take into account other parameters which are related to the output or the operation of the laser unit, either in addition or as an alternative to the input related to the temperature of the laser unit. Further details regarding the operation of the laser management module were provided above with reference to the control unit that is part of the system for providing a laser beam.

[095] Having described in some detail certain aspects of the present invention which are related to controlling of the operation of the laser module, the description of further embodiments of the invention continues with a description of further measures which may be implemented by the proposed system 10 in order to improve utility, efficiency and portability of the system 10.

[096] Reference is now made back to FIG. 1. According to some embodiments of the invention, the control unit 40 may also be configured to implement a modulation scheme with respect to a laser beam(s) output of the system 10. According to one example, the modulation scheme may be applied by a laser driver based on control signals received from the control unit 40. It would be appreciated that by implementing a modulation scheme and activating the laser unit(s) intermittently, the overall power consumption of the system may be reduced. This is because when the input current is turned off, the laser consumes no power, and does not generate heat (and thus reduces the cooling requirements from the cooling unit). However, surprisingly, the benefit in terms of power efficiency does not necessarily mean a penalty in terms of detectability. Rather, according to some embodiments of the invention, a modulation scheme may be implemented by the control unit 40 which renders the laser beam output of the system 10 compatible with a visual sensitivity parameter of the human eye and thus increases detectability of the laser beam output when viewed by a human (through a thermal imaging unit). This aspect of the invention is also described in further detail below.

[097] According to some embodiments of the invention, the control unit 40 may be configured to provide a specific target modulation scheme by applying, directly or indirectly an intermittent activation protocol with respect to the semiconductor laser unit(s) 22. For example, according to the modulation scheme, the control unit 40 may be configured to cause the semiconductor laser unit(s) 22 to be intermittently activated and deactivated according to a specific activation protocol. Further by way of example, in accordance with the modulation scheme, the control unit 40 may be configured to cause the semiconductor laser unit(s) 22 to be intermittently activated and deactivated, so that a substantial portion of the energy of the laser beam output of the system 10 is in a frequency band between 0.1-25Hz. In accordance with a further example, based on the modulation scheme, the semiconductor laser unit(s) 22 may be intermittently activated and deactivated, so that within a frequency range that is between 0.0 IHz - 10,000Hz, a substantial portion of the energy of the laser beam output of the system 10 is in a frequency band between 0.1-25Hz. Yet further by way of example, the semiconductor laser unit(s) 22 may be intermittently activated and deactivated, such that within the 0.01Hz - 10,000Hz frequency range, a substantial portion of the energy of the laser beam output of the system 10 is in a frequency band between 0.3-3Hz.

[098] Reference is now additionally made to FIG. 6A which provides an illustration of a possible modulation scheme in a constant frequency and of its respective frequency power distribution. Take for example a modulation scheme where the laser is on for a time duration which is equal to Δt within any period of τ. The Fourier Transform of such a modulation scheme can be generally described by peaks which are 1/τ apart, constrained by an envelope which is about 1/Δt wide, peaking around zero.

[099] It would be appreciated that by implementing the proposed modulation scheme as described above, the overall power consumption of the system may be reduced. This is because when the input current is turned off, the laser consumes no power, and does not generate heat (and thus reduces the cooling requirements from the cooling unit). Therefore, implementing a modulation scheme with a relatively short duty cycle (e.g. duty cycle of 25%) may contribute towards a reduced power consumption, without reducing (or with only slightly reducing) the detectability of the laser beam by or through a TIU.

[0100] Furthermore, as will be described in further detail below, the inventors of the present invention have discovered that in addition to power savings, the modulation may contribute to the detectability of the laser beam output by the human eye (when viewing the laser beam output through a thermal imaging device). Specifically, providing a laser beam output that is pulsed or modulated at a frequency band between approximately 0.1- 25Hz, and according to further embodiments, between 0.3-3Hz, may increase the detectability of the laser beam output of the system 10 when viewed by a human (through a thermal imaging unit). Reference is now made to FIG. 6B which provides a schematic illustration of the sensitivity of the human eye to flicker. As is shown in FIG. 6B, the sensitivity of the human eye to flicker increases up to a frequency of about 1 IHz, and then begins to drop. Research has led to somewhat different results, and according to this research, sensitivity of about to 1.5Hz is the optimal flicker frequency for the human eye.

[0101] Thus, modulating the semiconductor laser unit(s) 22 at a relatively short duty cycle may, in the context of some embodiments of the present invention, contribute both to a reduction in the power consumption of the system and to the detectability of the laser beam output produced by the system 10. It would be appreciated that having a system which is characterized by relatively low power consumption and which maintains good output detectability is in line with what is expected from a portable, small, efficient system that is able to provide good performance and versatility. It would be further appreciated that semiconductor lasers can be readily modulated at high frequencies. Furthermore, while semiconductor lasers can be turned on and off at high frequencies of MHz, heat plates and black-bodies have thermal time constants which are typically much slower, in the order of seconds to minutes.

[0102] According to some embodiments of the invention, the control unit 40 may control the activation (and deactivation) of the semiconductor laser unit(s) 22 through modulating the input current to the laser. According to some embodiments of the invention, the control unit 40 may provide control signals to a laser driver unit (not shown) that is adapted to activate the laser unit 22, and thus a certain pulse repetition rate (PRR) may be enforced.

[0103] According to further embodiments of the invention, the control unit 40 may be configured to provide a specific target modulation scheme by intermittently blocking the optical path of the laser beam and thus prevent laser energy from being emitted out of the system 10. For example, according to the modulation scheme, the control unit 40 may be configured to repeatedly block and unblock the optical path of the laser beam out of the system, such that the laser beam that is actually allowed to propagate out of the system 10 appears to be pulsed or modulated according to the modulation scheme implemented by the control unit 40. The control unit 40 may include or may be associated with various mechanical and/or electromechanical components which are collectively adapted to repeatedly block and unblock a laser beam from propagating in a certain direction, including, but not limited to, electromechanical shutter systems, acousto-optical shutters, electro-optical shutters and polarization-modulated shutters.

[0104] Having described some aspects of the invention which are related to the control unit 40, there is now provided a description of various embodiments of the invention which are related to the semiconductor laser module 20. According to some embodiments of the invention, the semiconductor laser module 20 may be adapted to produce a beam of laser energy at least within a first and a second wavelength bands, the first wavelength band being between approximately 3μm-5μm and said second wavelength band being between approximately 8μm-12μm.

[0105] It would be appreciated by those of ordinary skill in the art, that many thermal imaging units operate within the Mid Wave IR spectral range (or MWIR), typically between 3μm-5μm, and/or within the Long Wave IR spectral range (or LWIR), typically between 8μm-12μm. Such thermal imaging units include, for example, but are not limited to, InSb (Indium-antimonide) or MCT (Mercury Cadmium Telluride) cooled arrays which typically operate within the MWIR spectral range (3μm-5μm), and/or bolometric arrays which typically operate within the LWIR spectral range (8μm-12μm).

[0106] According to some embodiments of the invention, the semiconductor laser module 20 may include one or more semiconductor laser unit(s) 22 that is/are capable of producing at least one beam of laser energy having a wavelength that is between approximately 3μm-5μm or that is between approximately 8μm-12μm. According to a non-limiting example, the semiconductor laser unit(s) 22 may utilize one of the following laser technologies: Lead Salt lasers diodes, Antimonide lasers, Quantum Cascade Lasers (QCL) and Interband Cascade lasers (ICL). [0107] According to further embodiments of the invention, the semiconductor laser module 20 may include a QCL laser unit(s). It would be appreciated that currently QCL and ICL are capable of room temperature operation (or TEC cooled temperatures of typically -3O⁰C and above) while providing a power level of hundreds of milliwatts. Currently, QCL has some performance advantages over ICL, especially in the 8-12μm wavelength band. Moreover, QCL is currently easier and cheaper to manufacture compared to ICL, especially where units that are configured for providing an output at the 3-5μm band are concerned. Accordingly, QCL lasers may be used as part of some embodiments of the invention. It should be noted however, that further embodiments of the invention are not limited in this respect and that other types of semiconductor lasers may be used to provide at least one beam of laser energy having a wavelength that is between approximately 3μm-5μm or that is between approximately 8μm-12μm.

[0108] Having discussed various aspects of the laser technology which may be implemented as part of some embodiments of the invention, various implementations of the semiconductor laser module 20 and of other components of the system 10, are now described. According to further embodiments of the invention, the semiconductor laser module 20 may include one or more semiconductor laser units 22, and each of the semiconductor laser units 22 is configured to produce a laser energy with a wavelength that is between either the MWIR wavelength band (between approximately 3μm-5μm) or the LWIR wavelength band (between approximately 8μm-12μm). For example according to some embodiments of the invention, the semiconductor laser module 20 may include a QCL which is configured to emit laser energy in the MWIR or in the LWIR band. The QCL may include a plurality of active regions (for example, tens of active regions) in a cascaded design separated by a region that is commonly referred to as "an injector". The active regions may be tuned to emit light at substantially the same wavelength, for example, at a wavelength that is within the MWIR or in the LWIR band and thus produce laser energy at the desired wavelength.

[0109] According to further embodiments of the invention, the semiconductor laser module 20 may include a QCL that is configured to simultaneously produce laser energy that is characterized by a wavelength that is between the MWIR and LWIR wavelength bands. The QCL may include split active regions, for example, the QCL may include two (or more) segments of active regions. Each segment of the active regions may be tuned to emit photons in a different wavelength, a first segment may be tuned to emit photons at wavelength that is within the MWIR band, and a second may be tuned to emit photons at wavelength that is within the LWIR band.

[0110] As a further embodiment of the invention, the semiconductor laser module 20 may include (at least) a first and a second QCL, where the first QCL is configured to provide photons at a wavelength that is within the MWIR band and the second QCL be tuned to emit photons at a wavelength that is within the LWIR band, and a laser module controller (not shown) may be used to determine which one or whether both QCLs should be activated at any time instance. The laser module controller may be configured to control the semiconductor laser unit's output according to a predefined rule or criterion and/or the laser module controller may operate according to a manual selection made by an operator of the system 10. The laser module controller may be part of the system's control unit 40 or a dedicated separate component may be used.

[0111] Reference is now made to FIG. 7, which is a block diagram illustration of a system for providing a laser beam comprising at least a first and second semiconductor laser unit(s), the first semiconductor laser unit being configured for producing laser energy which is characterized by a wavelength that is between approximately 3μm-5μm, and the second semiconductor laser unit being configured for producing laser energy which is characterized by a wavelength that is between approximately 8μm-12μm, according to some embodiments of the invention. As is shown in FIG. 7, and according to some embodiments of the invention, the semiconductor laser module 220 may include at least a first and a second semiconductor laser units 222 and 224, the first semiconductor laser unit 222 may be configured to produce a beam of laser energy having a wavelength that is between approximately 3μm-5μm, and the second semiconductor laser unit 224 may be configured to produce a beam of laser energy having a wavelength that is between approximately 8μm-12μm.

[0112] Further with reference to FIG. 7, according to some embodiments of the invention, the system for providing a laser beam 20 may include a laser beam combining module 260. According to some embodiments of the invention, the laser beam combining module may be adapted to aim a laser beam produced by at least one of said first and second semiconductor laser units 222 and 224, such that a laser energy produced by the first semiconductor laser unit 222 and a laser energy produced by the second semiconductor laser unit 224 substantially overlap in the far-field.

[0113] According to some embodiments of the invention, and as is shown in FIG. 7, the beam combining module 260 may include a dichroic element. As is well known, a dichroic element is configured to selectively pass light or laser energy that is characterized by a wavelength that is within a specific wavelength band while reflecting light or laser energy having a different wavelength (this is outside the specific wavelength band). Thus, according to some embodiments of the invention, the beam combining module 260 may include a dichroic element which is configured to pass laser energy whose wavelength is approximately between 3μm-5μm while reflecting light or laser energy having a different wavelength (including the 8μm-12μm wavelength band). According to still further embodiments of the invention, the dichroic element may be configured to reflect light or laser energy whose wavelength is approximately between 8μm-12μm while allowing laser energy having a different wavelength (including the 3μm-5μm wavelength band) to pass through (or vice-versa).

[0114] It would be appreciated that the beam combining module 260 may include other elements which are able to selectively redirect laser energy from different sources and coming from different directions so as to enable a laser energy produced by a first semiconductor laser unit 222 and a laser energy produced by a second semiconductor laser unit 224 to substantially overlap or converge in the far-field. According to a further embodiment of the invention, the first and/or the second laser units 222 and 224 may be configured to produce a laser energy output that is characterized by a specific polarization state or orientation and the beam combining module 260 may include a polarization beam combiner, which is configured to reflect laser energy (or light) having a certain polarization state or orientation and to transmit or pass laser energy having a different polarization. Thus, according to some embodiments of the invention, the laser energy output of the first laser unit 222, for example, may be reflected by the polarization beam combiner at a certain angle, so that it substantially converges or overlaps with the laser energy output of the second laser unit 224, which the polarization beam combiner is configured to simply allow to pass through.

[0115] It would be appreciated that in case more than one semiconductor laser unit is included as part of the semiconductor laser module 220 by using combining optics 260 to converge in the far-field on the laser energy outputs of the semiconductor units, it may be possible to use a common optical collimating module 50 for collimating the output of each one of the semiconductor laser units. According to some embodiments of the invention, the laser energy output of each of the semiconductor laser units after being collimated by the common optical collimating module 50 may substantially overlap in the far field with one another.

[0116] Reference is now made to FIG. 8 which is a block diagram illustration of a system for providing a laser beam comprising a plurality (two or more) semiconductor laser units, and in association with each one of the a plurality of semiconductor laser units the system includes an optical collimating module, according to some embodiments of the invention. As is shown in FIG. 8 and according to some embodiments of the invention, a system for providing a laser beam may include a plurality of semiconductor laser units 322A-322C and each of the semiconductor laser units 322A-322C may be associated with an optical collimating module 350A-350C. It would be appreciated that by including a plurality of semiconductor laser units in the system 10 each with its own optical collimating module, a combining module may not be required.

[0117] As is shown in FIG. 7, and according to some embodiments of the invention, the system for providing a laser beam 10 may include an optical manipulation module 470. The optical manipulation module 470 may be adapted for being accommodated within said system 10 so that it can be selectively positioned in or out of an optical path of the laser beam(s) produced by the semiconductor laser module 20. According to further embodiments of the invention, the optical manipulation module 470 may be positioned in succession to the optical collimation module 50, so that the optical manipulation module (while in the optical path of the laser beam(s)) actually receives the beam(s) of laser energy output of the semiconductor laser module 20 after it has been collimated. According to some embodiments of the invention, the optical manipulation module 470 may be adapted to change the beam profile of a beam of light or of a laser beam that is incident thereupon. For example, according to one embodiment of the invention, the optical manipulation module 470 may be adapted to increase the divergence of a beam of laser that is incident thereupon. Thus, according to some embodiments of the invention, by inserting or removing the optical manipulation module 470 from the optical path of the laser beam(s) output of the semiconductor laser module 20, the divergence of the laser beam output of the system 10 may be modified.

[0118] According to some embodiments of the invention, the optical manipulation module 470 may include a negative optical element (e.g., a negative single element, or an assembly of optical elements which collectively form a negative optical element, or a diffractive element). When the optical manipulation module 470 is in a first operation mode, the negative optical element or assembly is positioned in the optical path of the laser beam(s) produced by the semiconductor laser module 20, whereas when the optical manipulation module 470 is in a second operation mode, the negative optical element or assembly is positioned out of the optical path of the laser beam(s) produced by the semiconductor laser module 20.

[01 19] According to some embodiments of the invention, the negative optical element or assembly may be positioned in the optical path of the laser beam produced by the semiconductor laser module 20 and may be positioned out of (removed from) the optical path of the laser beam produced by the semiconductor laser module 20 in accordance with and based upon an instruction or a selection by an operator of the system 10. The optical manipulation module 470 may include or may be associated with mechanical or electronic components which may be effective for moving the negative optical element or assembly into or out of the optical path of the laser beam energy produced by the semiconductor laser module 20. The negative optical element or assembly may be shifted into or out of the optical path of the laser beam energy produced by the semiconductor laser module 20 upon an appropriate selection by or instruction of an operator of the system 10 typically through an appropriate user interface. It would be appreciated that as mentioned above, according to some embodiments of the invention, the laser energy produced by the semiconductor laser module 20 is typically passed through a collimator and thus, when the negative optical element or assembly is in the path of the laser energy output of the semiconductor laser module 20, the laser energy will remain substantially focused and shall be characterized by a substantially small divergence angle.

[0120] According to some embodiments of the invention, the system for providing a laser beam may be configured to operate in a stand-off marking mode and in a self-marking mode, and the system 10 may be selectively switched between the stand-off marking mode and the self-marking mode. Switching from the target-market mode to the self- marking mode may involve modifying the shape or the cross-section or the divergence of the laser beam output of the system 10. According to some embodiments of the invention, the optical manipulation module 470 may enable the modification of the shape, cross-section or divergence of the laser beam output of the system 10.

[0121] According to some embodiments of the invention, the system for providing a laser beam 10 may be selectively operated at either a self-marking mode or at a stand-off marking mode. Additional reference is now made to FIGs. 9A and 9B. FIG. 9A is a graphical illustration of the system for providing a laser beam according to some embodiments of the invention, while being used in the stand-off marking mode. FIG. 9B is a graphical illustration of the system for providing a laser beam according to some embodiments of the invention, while being used in the self-marking mode.

[0122] As is shown in FIG. 9A, while in the stand-off marking mode, the system 10 may be used to provide a relatively narrow, focused laser beam 402. For example, at stand-off mode the system 10 may provide a laser beam output 402 that is characterized by a divergence angle that is less than 1 milliradian.

[0123] As mentioned above, the divergence angle of the laser energy is relatively narrow coming out of the optical collimating module 50. According to some embodiments of the invention, in case an optical manipulation module 470 is used to enable a selective modification of the beam profile or the shape of a laser beam output of the system 10, while the system 10 is in the target-marking mode, the optical manipulation module 470 may be operated so that it does not interfere with the collimated laser beam and thus the relatively narrow divergence angle of the laser beam coming out of the collimator 50 is maintained. For example, in case the optical manipulation module 470 is configured to selectively introduce a negative optical element or assembly 470 into the optical path of the laser energy (or laser beam) after the laser energy is passed through the collimating module 50, the negative element 470 may be positioned outside the optical path of the laser energy while the system 10 is in the stand-off marking mode.

[0124] As is illustrated by FIG. 9A, the system for providing a laser beam 10 may be located some distance away from the target 404. According to some embodiments of the invention, the throughput of the system for providing a laser beam 10 may be in the order of tens to hundreds of milliwatts. It would be appreciated that a throughput of this magnitude may enable an operator of a thermal imaging unit to detect a signature 406 of a laser beam produced by the system and aimed at the target, when the system is within hundreds to thousands of meters from the target and the thermal imaging unit 408 is within hundreds to thousands of meters from the target. The laser beam 404 signature is illustrated in FIG. 9A as a dark spot 406 on a display screen 412 of the TIU 408.

[0125] As an example for computing the required laser power, one may obtain from FIG. 10, which provides a Spectral Radiance Contrast graph, the value 0.02W-m^"2-λ^"'-μm^'1-sr^"1 of 300⁰K at 4μm, which represents the spectral irradiance contrast dL_λ /dT, meaning the change of the plank curve as a function of temperature. Taking into account an ITU with pixel resolution of d==30cm at the target, a laser spot at the target covering »=10 pixels, a target emissivity of 77=0.8 (thus reflectivity of 0.2), assuming that the weighted average spectral coverage of the ITU within the 3-5μm is Δλ~lμm, and that we would like that the laser matches the contrast of ΔT~1°K at the ITU, we can calculate the laser power (P) from:

[0126] ^P^^~Φ = η^ATAλ eq. 1

[0127] Plugging the mentioned parameters, we obtain P=226mW. This calculation neglects the effect of atmosphere (which may be different for the blackbody emission of the target and for the laser), and it assumes that the detection of the laser spot is possible if it creates a difference in radiation which is equivalent to the difference in radiation between two objects whose temperature difference is approximately ΔT~1°K. Similar calculation can demonstrate that the laser power in the LWIR which is required to generate the same thermal contrast in the ITU is about an order of magnitude higher.

[0128] As mentioned above, in accordance with some embodiments of the system for providing a laser beam, it is possible to provide the aforementioned relatively high throughput without imposing a substantial penalty, neither in terms of excessive power consumption, nor at the expense of access weight or cumbersome physical dimensions. For example, divergence of 0.5milliradian, and two lasers each with output laser power of 200mwatt working at a laser temperature of O⁰C can be implemented with a collimator with a diameter of a 20mm, and with a system power consumption of less than 20Watts. The volume of the entire system will then be of the order of 1-2 liters, and the weight will be approximately 2kg. It would be appreciated that all of the above values were provided by way of example only.

[0129] In FIG. 9B, there is illustrated a usage of the system for providing a laser beam 10 while in the self-marking mode, to signal a location of a unit (e.g., a person or a vehicle) that is associated with the system 10 to a other unit, which in the case of FIG. 9B happens to be a soldier 411 (top section) and a helicopter 413 (bottom section). According to some embodiments of the invention, while in the self-marking mode, the system for providing a laser beam 10 may be used to provide a relatively wide, diffused laser beam 403 that is characterized by a relatively wide divergences angle. For example, while in the self-marking mode, the system 10 may be used to provide a laser beam whose divergence angle is between 5-90 degrees. The divergence angle is wider because it is intended to be operated by a user who may not know precisely where the thermal imager 409 is located, and will not be able to aim the beam 403 with precision at the thermal imager 409. However, the wider the beam divergence, the smaller the angular laser intensity, and therefore the detection spectral range of the laser beam 403. As will be described in further detail below, embodiments of the present invention make use of innovative solutions which enable sufficient energy to be transmitted (and possibly reflected) over significant distances while complying with challenging requirements which may include any one of the following: portability, size, power consumption, performance, versatility and compatibility.

[0130] As mentioned above, the divergence angle of the laser energy is relatively narrow coming out of the optical collimating module 50, and an optical manipulation module 470 may be used according to some embodiments of the invention to enable a selective modification of the beam profile or the shape of a laser beam output of the system 10. As was described above, while the system 10 is in the self-marking mode, the optical manipulation module 470 may be used to increase the divergence of the relatively focused collimated laser beam. For example, in case the optical manipulation module 470 is configured to selectively introduce a negative optical element or assembly 470 into the optical path of the laser energy (or laser beam) after the laser energy is passed through the collimating module 50, the negative element 470 may be positioned in the optical path of the laser energy while the system 10 is in the self-marking mode.

[0131] As is illustrated by FIG. 9B, the system for providing a laser beam 10 may be located some distance away from the thermal imagining unit 409 to which the operator of the system 10 may be interested to signal his location. Also, since the divergence angle of the laser beam output 403 of the system 10 is relatively wide when the system 10 is in the self marking mode, the operator of the system 10 can signal his location over a relatively wide sector. For example, the system 10 may provide an effective coverage within a sector that is tens of degrees wide and over a distance of several kilometers. It would be appreciated that in order to achieve effective coverage within a sector of this magnitude, the throughput of the system 10 should be in the order of tens to hundreds of milliwatts. As mentioned above, the system for providing a laser beam 10 according to some embodiments of the invention is capable of providing a throughput that is of this magnitude without imposing a substantial penalty, neither in terms of excessive power consumption, nor at the expense of access weight or cumbersome physical dimensions. In fact, the parameters will be similar to those described above in connection with the stand-off mode, with the addition of the optical manipulation module 50 being introduced into the path of the laser energy.

[0132] Reference is now made to FIG. 11, which is a block diagram illustration of a system for providing a laser beam which includes an optical collimating module that can be selectively positioned in or out-of the optical path of the laser energy output of the semiconductor laser module, according to some embodiments of the invention. According to some embodiments of the invention, and as was mentioned above, the system for providing a laser beam may be selectively operated at a stand-off marking mode or at a self-marking mode. According to some embodiments of the invention, switching between the self-marking mode and the stand-off marking mode may be achieved by inserting or removing the optical collimating module 550 into or out of (respectively) the optical path of the laser energy output of the semiconductor laser module 20.

[0133] The optical collimating module 550, as is well known, is used to collimate laser (or light) energy that is passed therethrough. By passing the laser energy output of the semiconductor laser module 20 the divergence of the laser energy output is reduced and a collimated laser beam is achieved. As would be appreciated, the collimated laser beam may be suitable for target-marking applications, and thus, the desired beam profile for the system's 10 output laser beam may be achieved by introducing the optical collimating module 550 into the optical path of the laser energy output of the semiconductor module 20.

[0134] However, for the self-marking mode of the system 10 a wider divergence angle may be more suitable, and thus, according to some embodiments of the invention, while the system 10 is in the self-marking mode, the optical collimating module 550 may be positioned out of the optical path of the laser energy output of the semiconductor module 20, thereby allowing the laser energy exiting the semiconductor module 20 to diverge substantially according to its spontaneous divergence. It would be appreciated that allowing the laser energy to diverge substantially according to its spontaneous divergence may give rise to a laser beam output that is characterized by a divergence angle that is in the order of 30 degrees Full Width Half Max (FWHM), in both the slow and fast axes. It would be appreciated that although the term "laser beam" is sometimes used to described a beam of laser energy that is characterized by, among other things, being collimated, as part of the description of some embodiments of the invention, the term "laser beam output of the system" or the like, are not limited in terms of the divergence angle (or the level of collimation) of the laser energy.

[0135] Having described various aspects of the invention which are related to the divergence of the laser beam output of the system, there is now provided a description of some aspects of the invention which are related to the cooling of the laser system. As mentioned above, a laser system which includes a semiconductor laser unit(s) and which utilizes a semiconductor laser unit to generate a laser energy output that is characterized by a wavelength longer than 3μm and which is expected to provide output power that is in the order of tens to hundreds of milliwatts, would require a cooling unit in order to be able to operate effectively and for a meaningful period of time at ambient temperatures.

[0136] Referring back to FIG. 1, according to some embodiments of the invention, the cooling unit 80 may be configured to cool the components of the system 10. For example, according to some embodiments of the invention, each one of the semiconductor laser unit(s) 22 may be associated with the cooling unit 80 (either a common unit or two separate units), and the cooling unit 80 may be configured to cool the semiconductor laser unit 22. The cooling unit 80 may also be adapted to cool the optical collimating module 50. The cooling unit 80 may be used to cool additional components of the system 10. According to further embodiments of the invention, the system 10 may include several cooling units and each cooling unit may be used to cool one or more components of the system 10. According to still further embodiments of the invention, a single unit may be used to cool several components of the system and possibly several semiconductor lasers.

[0137] According to some embodiments of the invention, the cooling unit 80 may include a Thermo-Electric Cooling unit (abbreviated: TEC). A TEC may cool the laser from an ambient temperature of 4O⁰C to about O⁰C. The TEC may be 1, 2, or 3 stage TEC. According to one embodiment, the TEC is a single stage, in order to reduce cost, increase reliability and decrease cooling time. One example of a TEC unit which may be used as part of some embodiments of the invention for cooling the semiconductor laser units and other components of the system is disclosed in US Patent No. 5,640,407 to Freyman, et al.

[0138] According to a further aspect of the invention, there is provided a cooling system which comprises a heat-pump component that is coupled to a phase changing material. According to one embodiment, the proposed cooling system may be used as part of the proposed system for providing a laser system described above. The proposed cooling system may be used to cool the semiconductor laser unit(s) and/or other components of the system for providing a laser beam. According to a further embodiment of the invention, the proposed cooling system may be associated with the proposed device for managing operation of a semiconductor laser unit.

[0139] Reference is now made to FIG. 12 A, showing a block diagram illustration of a system for providing a laser beam, which includes a heat-sink component that is coupled to a phase changing material, according to some embodiments of the invention. Additional reference is made to FIG. 12B which is an isometric view of the system shown in FIG. 12A.

[0140] A cooling module (or unit) 80, may include a heat-pump component 81 and a phase changing material (PCM) compartment or reservoir 84. According to one example, the heat-pump 80 may be a TEC unit. The PCM compartment 84 may be substantially filled with a PCM 86, typically a PCM that is in a solid state at typical ambient temperatures. It would be appreciated that there is a wide range of commercially available PCMs, and that different PCMs may be characterized by different typical melting temperatures. For example, Rubitherm Technologies GmbH of Berlin, Germany, offers a range of latent heat paraffins, each with a different melting temperature, and the range offered covers meting temperatures from -3°c to 99°c- The specific selection of which PCM to use may depend upon the following non-limiting factor: the typical ambient temperature at the area where the system is to be used 10. As will be described in further detail below, the PCM compartment or reservoir 84 may be detachable and the specific PCM compartment 84 used at any particular time may be selected according to the specific usage profile expected for that time.

[0141] As mentioned above, the cooling unit 80 may be used to cool the semiconductor laser module 20, and specifically the semiconductor laser unit 22, and/or any other components of the system 10. The cold side 82 of the heat-pump component 81 may be thermally coupled to a semiconductor laser module 20 of the system 10 and/or to any other component of the system 10 which requires cooling. The hot side 83 of the heat- pump component may be thermally coupled to the PCM compartment 84. Thus, the heat- pump 81 may be used to draw or remove heat from the semiconductor laser module 20, for example, and to transfer the heat (or energy) to the PCM 86 within the PCM compartment 84.

[0142] According to some embodiments of the invention, the system 10 may be configured such that, while the system 10 is idle, and specifically, while the semiconductor laser unit 22 is idle, the temperature of the hot side 83 of the heat pump 81 is typically below the melting temperature of the PCM 86. Typically, while the semiconductor laser unit 22 is idle, its temperature would be close to the ambient temperature (unless it had been recently activated and has not yet sufficiently cooled down), and thus by selecting a PCM 86 that is characterized by a melting temperature that is above the typical ambient temperature, the PCM 86 would be kept in its solid state while the semiconductor laser unit 22 is idle. According to further embodiments of the invention, the system 10 may be configured such that, shortly after the system 10 is activated, and specifically, shortly after the semiconductor laser unit 22 is activated, the temperature of the hot side 83 of the heat pump 81 would cross the melting temperature of the PCM 86. If the melting temperature of the PCM 86 is moderately higher than the ambient temperature, as the hot side 83 begins to accumulate heat and its temperature rises substantially above the ambient temperature, the PCM 86 would begin to melt.

[0143] From a thermal point of view, the proposed configuration of the system 10 and of the cooling unit 80 is generally as illustrated by the graph shown in FIG. 13 to which reference is now made. As is shown in FIG. 13 and according to some embodiments of the invention, while the system 10 is idle, and specifically, while the semiconductor laser unit 22 is idle, the temperature Ti of the hot side 83 of the heat pump 81 is typically below the melting temperature of the PCM 86 and the PCM 86 is, at least in part, in its solid state. Once the semiconductor laser is activated and a temperature difference begins to develop between the hot side 83 of the heat pump 81 and the PCM 86, the PCM 86 starts to absorb heat (energy) from the hot side 83 of the heat pump 81. Initially the heat (energy) absorbed from the hot side 83 may be translated to sensible heat of the PCM 86, or in other words may increase the temperature of the PCM 86 in its solid state. At this stage, if more heat (energy) is transferred from the hot side 83 to the PCM 86, the temperature of the PCM 86 would gradually increase while the PCM 86 is in its solid state. [0144] The thermodynamic behavior of the PCM 86 changes significantly once the melting temperature is reached. If enough heat (energy) is transferred from the hot side 83 to the PCM 86 (for example, when the semiconductor laser unit 22 is activated beyond a certain period of time), at some point, the PCM's 86 temperature would reach the PCM's melting temperature and the PCM 86 would begin to melt. It would be appreciated that when a solid PCM is heated up and reaches its melting point, it goes through a state change, from solid to liquid. During this process the PCM 86 absorbs a certain amount of additional heat, known as melting enthalpy, and despite the additional heat input, the temperature of the PCM stays substantially constant, even though phase change is taking place. In other words, at the melting stage, even as more heat (energy) is removed from by the PCM 86 from the hot side 83, the temperature PCM 86 would not rise. Similarly, when the phase change process is reversed, that is from liquid to solid, the stored latent heat is released, again at a nearly constant temperature.

[0145] The thermodynamic behavior of the PCM 86 changes again when all the PCM 86 has melted. Once substantially all the PCM 86 has melted, and the PCM 86 is entirely liquid, additional heat (energy) transfer from the hot side 83 to the PCM 86 would induce more sensible heat, and the temperature of the PCM 86, this time in its liquid state, would gradually rise. At some point, depending upon the configuration of the system 10, the temperature of the PCM 86 may become substantially equal to the temperature of the hot side 83 of the heat pump 81 and the PCM's 86 ability to remove energy from the hot side 83 of the heat pump 81 may be substantially reduced and may even become close to zero.

[0146] According to some embodiments of the invention, the control unit 40 may deactivate the semiconductor laser unit 22 when the temperature of the PCM 86 crosses a predefined threshold. According to a further embodiment of the invention, the control unit 40 may be configured to deactivate the semiconductor laser unit 22, when the temperature of the PCM 86 approaches the temperature of the hot side 83 of the heat pump 81.

[0147] The specific heat capacity of latent heat paraffins is about 2,1 kJ/(kg-K). Their melt enthalpy is approximately between 120 and 160 kJ/kg. The combination of these two values results in a relatively high energy storage density. For illustration, latent heat paraffins/waxes offer four to five times higher heat capacity by volume or mass than water at low operating temperature differences.

[0148] The combination of the heat pump 81 with the PCM 86 may provide significant advantages particularly in the service of a portable system for providing a laser beam in accordance with embodiments of the invention. According to some embodiments of the invention, the combination of the heat pump 81 with the PCM 86 may be particularly advantageous for a transient cooling system. According to further embodiments of the invention, the combination of the heat pump 81 with the PCM 86 may provide fast and efficient cooling for a limited period of time (although the amount of time can be ample for many applications). According to still further embodiments of the invention, the combination of the heat pump 81 with the PCM 86 may enable to construct a transient cooling unit that is characterized by being relatively light, compact, reliable and that is highly efficient, both in terms of power consumption to heat absorption and heat storage, and in terms of thermodynamic performance. The proposed cooling unit may provide additional advantages. Some of the advantages of the proposed cooling unit shall be described below in further detail.

[0149] The combination of the heat pump 81 with the PCM 86 lends itself to efficient heat transfer mechanism design due to the good convection coefficient of the PCM 86, and the ability to design the path from the semiconductor laser module 20 to the PCM 86 such that it introduces only low thermal resistance. Efficient heat transfer may enable fast cooling of the semiconductor laser module 20 and thus may enable to achieve a relatively strong output laser beam within a relatively short period of time without being required to use constant cooling solutions. Furthermore, since throughout the melting process the temperature of the PCM 86 remains constant despite the large amount of additional energy that is evacuated from the hot side of the heat pump, an effective operating temperature can be maintained at the hot side of the heat pump. It is estimated that the operating temperature at the hot side of the heat pump can be (during the melting phase) 15-20°K lower with PCM compared to a typically heatsink and fan solution. It would be appreciated that this advantage would typically exist during or around the melting phase (as long as not all the PCM has melted and the temperature of the PCM remains substantially constant), and is therefore particularly significant for the proposed transient cooling solution. A summary of the advantages of the proposed cooling unit is provided below.

[0150] The heat pump of the proposed cooling unit can work in a more efficient regime because of the fact that the temperature at the hot side of the heat pump is determined by the PCM melting point.

[0151] The proposed cooling unit can be kept in a sleep mode while the semiconductor laser is idle without being required to preserve a low working temperature for the laser. The low laser thermal capacity of the laser, and the laser's relatively low thermal resistance to the heat pump, as well as the low thermal resistance across the heat pump being relatively low, enable fast cool-down time once the system and/or cooling unit is switched to active mode.

[0152] Constant PCM melting temperature and large contact area between the heat pump and PCM particles produce a very effective operating temperature at the hot side of the heat pump.

[0153] The need for using a cooling fan in field portable laser systems is eliminated. Instead, the proposed cooling system can be designed as a fully sealed unit without any moving parts.

[0154] Improved efficiency of the heat transfer mechanism between the heat pump and the PCM reservoir, since PCM, particularly in its liquid state, has a much better convection coefficient than ambient air. It would be appreciated that the cooling unit can be constructed, according to some embodiments of the invention, such that initial liquidation of the PCM would occur within a relatively short interval following the activation of the laser.

[0155] The heat reservoir time of operation and size/weight can be optimized and produced using the concept of "magazines". The magazines may be replaceable, and when the thermal storage of one magazine is substantially depleted it may be easily replaced with another, and thereby extend the operation time of the laser without hampering performance. A PCM magazine can be reused after it cools down.

[0156] Throughout the description of the present invention, some embodiments are described as being part of a portable unit, system or device. Further discussions describe some embodiments of the invention as being particularly advantageous for being used in conjunction with a portable unit, system or device. It should be noted however that some embodiments of the invention of the present invention are not limited in this respect. Rather, further embodiments of the invention may be implemented as part of a unit, system or device that is not intended for being hand-carried or otherwise carried by a person. For example, some embodiments of the present invention may be implemented in conjunction with or as part of a unit, system or device that is mounted on a vehicle, such as an aircraft. It would be appreciated that embodiments of the present invention which are intended for being implemented in conjunction with more complex systems or systems which are intended to be mounted on a platform that is less demanding in terms of size and weight of the payload mounted on the platform compared to a human being, may be somewhat modified compared to a portable system. For example, a modified version of the system for providing a laser beam shown in FIG. 1 or of the system for providing a laser beam shown in FIG. 12A may be provided according to some embodiments of the invention with some changes for being mounted on an aircraft. The aircraft mounted system may be used for example to counter missiles or other threats directed towards the aircraft. Further by way of example, the aircraft mounted version of the system for providing a laser beam shown in FIG. 1 may be implemented without the energy unit 30 and instead the energy source and power supply system onboard the aircraft may be used as the source of energy for the system 10.

[0157] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will occur to those skilled 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 true scope of the invention.

Claims

1. A system for providing a laser beam, said system comprising: at least one semiconductor laser unit adapted to produce laser energy having a wavelength longer than 3μm and that is detectable by a thermal imaging unit; a cooling unit adapted to cool at least said semiconductor laser unit; and a control unit adapted for activating said cooling unit in conjunction with or around activation of said semiconductor laser unit, such that said cooling unit is kept substantially inactive while said semiconductor laser is inactive.

2. The system according to claim 1, further comprising a portable electricity source configured and operable for powering components of said system.

3. The system according to any one of claims 1 or 2, wherein said control unit is adapted to determine drive parameters for controlling the operation of said semiconductor laser unit based at least on a temperature related input that is associated directly or indirectly with the temperature of said semiconductor laser unit.

4. The system according to claim 3, wherein said control unit is adapted to dynamically adapt the drive parameters for controlling the operation of said semiconductor laser unit based on a wavelength of the laser energy produced by said semiconductor laser unit.

5. The system according to claim 3, wherein said control unit is adapted to dynamically adapt the drive parameters for controlling the operation of said semiconductor laser unit based on a light power parameter related to the laser energy produced by said semiconductor laser unit.

6. The system according to any one of claims 3-5, wherein said control unit is adapted to dynamically adapt the drive parameters further based on a thermal damage parameter related to at least one component of said system.

7. The system according to any one of claims 3-6, wherein said control unit is adapted to determine drive parameters which are effective for adapting any one of the following: an input current that is used to power said semiconductor laser unit; a pulse repetition rate at which said semiconductor laser unit is operated; and a duty cycle at which said semiconductor laser unit is operated.

8. The system according to any one of claims 1-6, wherein upon receiving an instruction to activate said semiconductor laser unit, said control unit is adapted to determine whether the temperature of said semiconductor laser unit is above an initial temperature threshold, and if the temperature is above the threshold, the control unit is adapted to delay the activation of said laser unit until its temperature drops below the initial threshold.

9. The system according to any one of claims 1-8, wherein said control unit is adapted to turn-off said cooling unit at or around the time said semiconductor laser unit is turned-off.

10. The system according to any one of claims 1-3 ,where said control unit is adapted to optimize said system's laser beam output power or said system's power-to-light efficiency based at least on a temperature related input that is associated directly or indirectly with the temperature of said semiconductor laser unit.

11. The system according to any one of claims 1-10, wherein said semiconductor laser unit is adapted to produce a beam of laser energy at least within a first and a second wavelength band, said first wavelength band being between approximately 3μm-5μm and said second wavelength band being between approximately 8μm-12μm.

12. The system according to claim 11, where said at least one semiconductor laser unit comprises at least a first and a second semiconductor laser unit, said first semiconductor is adapted to produce a beam of laser energy within said first wavelength band and said second semiconductor laser unit is adapted to produce a beam of laser energy within said second wavelength band.

13. The system according to claim 12, wherein said at least one semiconductor unit comprises a semiconductor laser unit which is adapted to produce a beam of laser energy at least within said first and said second wavelength bands simultaneously.

14. The system according to any one of claims 11-13, wherein said at least one semiconductor laser unit comprises one or more one of the following laser technologies: Lead Salt lasers diodes, Antimonide lasers, Quantum Cascade Lasers (QCL) and Interband Cascade lasers (ICL).

15. The system according to any one of claims 1-14, wherein said cooling unit is a thermo electric cooler (TEC).

16. The system according to any one of claims 1-15, wherein said cooling unit comprises: a phase changing material (PCM) reservoir that is substantially filled with PCM; and a heat pump having a cold side that is thermally coupled to said semiconductor laser module and a hot side that is thermally coupled to said phase changing material (PCM) reservoir.

17. The system according to claim 16, wherein said PCM is characterized by a melting temperature that is above typical ambient temperatures, and wherein said heat pump is operated so that the operating temperature of the hot side of the heat pump is above the melting temperature of said PCM.

18. The system according to any one of claims 16 or 17, wherein said PCM reservoir is removable and replaceable.

19. The system according to any one of claims 1-18, wherein said control unit is adapted to implement in respect of a laser beam output of said system a modulation scheme, and said modulation scheme is based on an enhanced sensitivity of the human eye to changes in a scene.

20. The system according to claim 19, wherein said modulation is effective for controlling said laser beam output so that, within a frequency range that is between 0.0 IHz - 10,000Hz, a substantial portion of the energy of said laser beam output is in a frequency band between 0.1-100Hz.

21. The system according to any one of claims 1-20 wherein a total throughput of the system is in the order of tens to hundreds of milliwatts, and wherein a total power consumption of said system beam is in the order of a few watts up to a few tens of watts.

22. A system for providing a laser beam, said system comprising: at least one semiconductor laser unit adapted to produce laser energy having a wavelength longer than 3μm and that is detectable by a thermal imaging unit; and a control unit for dynamically adapting the drive parameters controlling the operation of said semiconductor laser unit based at least on a temperature related input that is associated directly or indirectly with the temperature of said semiconductor laser unit.

23. The system according to claim 22, further comprising a portable electricity source configured and operable for powering components of said system.

24. The system according to any one of claims 22 or 23,where said control unit is adapted to optimize said system's laser beam output power or said system's power-to-light efficiency based at least on said temperature related input.

25. The system according to any one of claims 22-24, wherein upon receiving an instruction to activate said semiconductor laser unit, said control unit is adapted to determine whether the temperature of said semiconductor laser unit is above an initial temperature threshold, and if the temperature is above the threshold, the control unit is adapted to delay the activation of said laser unit until its temperature drops below the initial threshold.

26. The system according to any one of claims 22-25, wherein said control unit is adapted to dynamically adapt the drive parameters further based on a thermal damage parameter related to at least one component of said system.

27. The system according to any one of claims 22-26, wherein said semiconductor laser unit is adapted to produce a beam of laser energy at least within a first and a second wavelength band, said first wavelength band being between approximately 3μm-5μm and said second wavelength band being between approximately 8μm-12μm.

28. The system according to any one of claims 22-27, wherein said cooling unit comprises: a phase changing material (PCM) reservoir that is substantially filled with PCM; and a heat pump having a cold side that is thermally coupled to said semiconductor laser module and a hot side that is thermally coupled to said phase changing material

(PCM) reservoir.