Passive high energy Q-switched laser system with optical synchronous multi-stage / multi-pass amplification

Abstract

A subnanosecond laser system is disclosed. The subnanosecond laser system may include a pump laser source operable to generate a pump laser beam having a pump wavelength; a first pump beam splitter operable to receive the pump laser beam and to split the pump laser beam into at least a first split pump laser beam and a second split pump laser beam; a passively Q-switched seed laser operable to receive the first split pump laser beam and generate a seed laser beam; and an amplifier assembly operable to receive the second separate pump laser beam and the seed laser beam. The amplifier assembly may include one or more amplifiers arranged in series in a multi-stage configuration, in a multi-pass configuration, or a combination thereof.

Description

Technical Field

[0001] The present system relates to a passive high energy Q-switched laser system, and in particular to a passive high energy Q-switched laser system with optically synchronized multi-stage / multi-pass amplification. Background Art

[0002] Lasers are used in many applications in industry, research, and medicine. Of particular interest are lasers that produce high energy and short duration pulses (e.g., nanosecond and sub-nanosecond pulses). Such lasers would facilitate material microprocessing applications with high precision. Such lasers could also address many scientific and technological applications and certain medical procedures where a brief interaction time with tissue can reduce heating effects, increase mechanical stress, and improve the quality of the interaction.

[0003] Q-switched solid-state lasers are currently used to generate short-duration laser pulses. These pulses typically have a duration as short as a few nanoseconds. More generally, active optical components (acousto-optic or electro-optic) are involved to generate Q-switched pulses. However, due to the limitations of the fast switching time of the active Q switch and the large physical size that leads to a longer cavity length, the pulse duration of the active Q-switched laser is limited to a few nanoseconds or longer. In order to further reduce the pulse duration, a mode-locked laser or a special type of Q-switched laser (commonly referred to as a microchip laser) will be used. Although mode locking can produce ultrashort laser pulses, its cavity involves a complex optical arrangement and is susceptible to environmental disturbances. In addition, the typical pulse energy generated from the mode-locked resonator is on the order of nanojoules (nJ). In order to generate millijoule energy for meaningful applications, the regenerative amplifier involving complex optical arrangements and precise electronic synchronization makes the entire system bulky, expensive and less reliable. Passively Q-switched short cavity lasers can provide a compact and cost-effective alternative to generate pulses in the sub-nanosecond region. A typical Q-switched short cavity laser consists of a laser medium, a saturable absorber as a passive Q switch, and two cavity mirrors (a high reflector and an output coupler). The cavity is designed in such a way that the crystal length is minimized, so the cavity length is on the order of millimeters. The short cavity length leads to an extremely short cavity lifetime and may produce much shorter Q-switched pulses. In the case of a high energy pump source combined with a saturable absorber with low initial transmittance, it is possible to produce >mJ. It has been demonstrated that a Q-switched short cavity laser can produce output pulses shorter than 150ps, as short as the pulses produced by large mode-locked lasers.

[0004] Since the energy from the Q-switched short cavity oscillator is high enough (in the millijoule level), it is not necessary to introduce a complex amplifier system (i.e., a regenerative amplifier) ​​to obtain a significantly large amplification factor as in a mode-locked laser for practical applications. In contrast, a master oscillator power amplifier (MOPA) system is typically used to generate sub-nanosecond, high-energy laser pulses. MOPA systems, especially those with high amplifier gain, are sensitive to parasitic reflections, which can lead to problems with spontaneous lasing. Spontaneous lasing can severely limit the amplification that can be achieved in a power amplifier. A single-stage amplifier with one-way amplification is a simple configuration. However, extracting high energy (>1J) is problematic. For a one-way or single-stage amplifier, in order to store higher gain for amplification, the amplifier must be strongly pumped. At the same time, the higher gain established in the amplification medium tends to promote the generation of amplified spontaneous emission (ASE) or spontaneous lasing, which in turn depletes the gain and limits the amplified output energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] For a more complete understanding of the present disclosure and its features, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like elements:

[0006] Figure 1 is an example of a sub-nanosecond laser system with an optically synchronized multi-stage / multi-pass amplifier assembly.

[0007] Figure 2 is an example of a passively Q-switched short-cavity seed laser.

[0008] Figure 3 is an example of an optically synchronized MOPA system with dual amplifier stages and a forward pumping configuration.

[0009] Figure 4 is an example of an optically synchronized MOPA system with dual amplifier stages and a backward pumping configuration.

[0010] Figure 5 is an example of an optically synchronized MOPA system with dual amplifier stages and a double-ended pumping configuration.

[0011] Figure 6 is an example of an optically synchronized MOPA system with three amplifier stages and a forward pumping configuration.

[0012] Figure 7 is an example of an optically synchronized MOPA system with a double-pass amplifier and backward pumping configuration.

[0013] Figure 8 is an example of an optically synchronized MOPA system with a combined double-pass and bipolar amplifier and backward pumping configuration.

[0014] Fig. 9 The principle of optical synchronization of a fully passive MOPA system with a two-stage amplifier is shown.

[0015] Fig. 10A is an example of self-energy stabilization achieved by optical synchronization of a passive QS seed laser with a two-stage amplifier at higher total pump energy.

[0016] Fig. 10B is an example of self-energy stabilization achieved by optical synchronization of a passive QS seed laser with a two-stage amplifier at low total pump energy.

[0017] Fig.11A is an example graph showing energy control by adjusting the Q-switching delay time in conjunction with optical synchronization for higher seed pump energy and constant amplifier pump energy.

[0018] Fig. 11B is an example graph showing energy control by adjusting the Q-switching delay time in conjunction with optical synchronization for lower seed pump energy and constant amplifier pump energy. DETAILED DESCRIPTION

[0019] It will be understood that, in order to make the description simple and clear, where appropriate, reference numerals may be repeated between different figures to indicate corresponding or similar elements. In addition, many specific details are set forth in order to provide a thorough understanding of the examples described herein. However, it will be appreciated by those of ordinary skill in the art that the examples described herein may be practiced without these specific details. In other cases, methods, procedures, and components are not described in detail to avoid blurring the related features described. Moreover, this description should not be construed as limiting the scope of the embodiments described herein. The accompanying drawings are not necessarily drawn to scale, and the proportions of certain parts may be enlarged to better show the details and features of the present disclosure.

[0020] Several definitions applicable throughout the above disclosure will now be presented.

[0021] As used herein, "about" refers to numerical values, including integers, fractions, percentages, etc., whether or not explicitly stated. The term "about" generally refers to a numerical range, for example, ±0.5%-1%, ±1%-5%, or ±5%-10% of the value, which will be considered equivalent to the value, for example, having the same function or result.

[0022] The term "coupled" is defined as connected, whether directly or indirectly through intervening components, and is not necessarily limited to physical connections. The connection may be such that the objects are permanently connected or releasably connected.

[0023] The term "substantially" is defined as conforming substantially to a particular size, shape, or other wording modified substantially such that the component need not be exact.

[0024] The terms "comprising," "including," and "having" are used interchangeably in this disclosure. The terms "comprising," "including," and "having" mean including but not necessarily limited to the things so described. The term "consisting essentially of is more restrictive than "comprising," but not as strict as "consisting of." Specifically, the term "consisting essentially of limits membership to the specified materials or steps and those that do not materially affect the basic characteristics of the claimed invention. The terms "a," "an," and "the" should be understood to cover the plural as well as the singular.

[0025] As used herein, the term "high energy, sub-nanosecond laser" or "sub-nanosecond laser" may refer to a laser that can provide energy of 0.1 J to 10 J and pulse duration of 10 picoseconds to 900 picoseconds. In general, high energy, sub-nanosecond lasers can provide, for example, more efficient micromachining, scientific spectroscopy, and medical treatments than commonly used nanosecond lasers. Thus, the availability of high energy, sub-nanosecond lasers can facilitate improvements in existing applications and support the development of new laser applications.

[0026] The terms used in this specification generally have their common meanings in the art in the context of the present disclosure and in the specific context in which each term is used. For any one or more of the terms discussed herein, alternative language and synonyms can be used, and no matter whether the terms are described or discussed in detail in this article, special meanings should not be given. In some cases, synonyms are provided for some terms. Enumerating one or more synonyms does not exclude the use of other synonyms. The use of examples (including examples of any terms discussed herein) anywhere in this specification is only illustrative, and is not intended to further limit the scope and meaning of the present disclosure or any example terms. Similarly, the present disclosure is not limited to the various embodiments provided in this specification.

[0027] A sub-nanosecond laser system having a passively Q-switched seed laser and an amplifier assembly is disclosed herein. The laser system described herein may overcome one or more of the problems described herein above with respect to previous Q-switched lasers by using a multi-stage or multi-pass amplifier in the amplifier assembly.

[0028] Multi-stage amplification involves two or more amplifiers arranged in series and separated by an isolator. For such a MOPA system, instead of depositing the pump energy into a single laser medium, the strong pump energy is distributed into multiple amplifier mediums, so the ASE or spontaneous lasing process can be mitigated. Therefore, it is a relatively simple and reliable solution to achieve high energy amplification. For a multi-pass MOPA system, since the seed beam travels back and forth through the amplifying medium multiple times, the gain can be efficiently extracted and used for the amplification of the seed laser. The efficient gain extraction will suppress the unwanted ASE or spontaneous lasing, thereby depleting the gain. Therefore, it can be a compact and cost-effective approach.

[0029] Typically, a MOPA with a multi-stage amplifier includes at least three pump sources, one of which pumps the master oscillator and the other pump sources pump the power amplifier. The pump may include a flash lamp or other light source. In the case of a commonly used multi-pass or multi-stage MOPA system, multiple separate pump sources are used. For proper MOPA operation, the pump sources and Q-switching operations must be tightly synchronized. However, synchronization requires a complex electronic system. Any electronic noise or fluctuations may cause significant unwanted energy variations. In addition, the use of complex electronic devices for timing synchronization may increase the complexity and cost of the system. The laser system described herein provides optical synchronization of a single pump laser for pumping a seed laser and a multi-pass and multi-stage amplifier, thereby avoiding all these problems. In addition, a laser system with a single pump laser can be cheaper than a laser system with a separate pump laser configured to pump a seed laser and one or more separate pump lasers configured to pump an amplifier system.

[0030] The MOPA laser system and method disclosed herein realizes optically synchronized multi-stage / multi-pass amplification with a short cavity Q-switched laser as a seed to produce a Joule-level sub-nanosecond laser beam. The entire MOPA system includes a passively Q-switched laser with a cavity length of several millimeters used as a seed laser, and the laser is followed by two or more amplifiers arranged in series or multi-pass configuration, or a combination of multi-pass and multi-stage amplifiers. In the disclosed MOPA laser system, there are no active components involved in achieving proper laser operation. Therefore, it is a fully passive method. The seed laser can produce millijoule-level laser pulses with nearly perfect beam quality and pulse duration as short as 50ps-150ps. One or more isolators can be positioned between the seed laser and the amplifier assembly. In an example, an isolator can be positioned between the seed laser and the amplifier assembly. In a multi-stage system, an additional isolator can be used between two adjacent stages. The isolator is operable to prevent any unwanted feedback from the current stage to the immediately preceding stage in order to prevent optical damage or passive Q-switching timing failure. A single pump source is used to pump both the seed laser and the amplifier. Therefore, synchronization of the seed laser with the multi-stage amplifier is achieved optically and automatically.

[0031] Some advantages of the disclosed method are: fully passive approach, optical synchronization for proper operation of multi-stage / multi-pass amplification, self-energy compensation, reliable performance and / or energy scaling. For example, the disclosed laser system can have much higher energy stability and can have less performance dependence on environmental changes (i.e., temperature, electronic noise, etc.) than electronically synchronized amplifier systems. It can also help reduce COG by eliminating any expensive optics used to achieve time synchronization and their expensive electronic drivers.

[0032] The fully passive approach means that no active components are used in the system. Q-switching is achieved using passive attenuators (i.e., saturable absorbers). No electronic drivers are required for timing synchronization of the seed laser pulses with the amplifier. Optical synchronization means that a single pump source is used for both the seed laser and the amplifier, which enables timing synchronization to be achieved optically without introducing any electronic components. This also allows for proper operation of multi-stage / multi-pass amplification. Self-energy compensation means that optical synchronization can help mitigate any amplified output energy variations due to pump energy fluctuations. Fig. 10A As shown in , higher pump energies will result in a shorter time for the stored energy to overcome the Q-switching threshold to generate Q-switched laser pulses from the seed laser. For the amplifier, a shorter Q-switching delay time helps to balance the higher gain in the amplifying medium due to the higher pump energy. Therefore, the available stored energy for extraction can be the same and no greater amplified energy may be produced. On the other hand, as Fig. 10BAs shown, if the pump energy is low, the longer QS delay time will leave enough time for energy storage in the amplifying medium to offset the reduction in gain. Therefore, this passive Q-switching and optical synchronization of the amplifier serves as an energy self-stabilization mechanism to mitigate pump laser energy fluctuations. The reliable performance means that the fully passive optically synchronized system is insensitive to electronic noise and less susceptible to environmental changes compared to electronically synchronized MOPA systems. Energy scaling is provided by a modular amplifier configuration of multi-stage amplifier components. Since each stage can be regarded as an independent amplifier, energy scaling can be achieved more easily by adding more stages of amplifiers without complicating the system setup (especially synchronization) and alignment of the previous stages.

[0033] Figures 1 to 8 Various exemplary embodiments of a high energy, sub-nanosecond laser system are presented. The disclosed high energy, sub-nanosecond laser system 100 includes: a pump laser source 102, the pump laser source operable to generate a pump laser beam having a pump wavelength; a first pump beam splitter 104, the first pump beam splitter operable to receive a pump laser beam 103 and separate the pump laser beam into at least a first separate pump laser beam 105 and a second separate pump laser beam 107; a passively Q-switched seed laser 110, the passively Q-switched seed laser operable to receive the first separate pump laser beam 105 and generate a seed laser beam 109; and an amplifier assembly 120, the amplifier assembly operable to receive the second separate pump laser beam 107 and the seed laser beam 109, the amplifier assembly 120 comprising one or more amplifiers. The one or more amplifiers may be arranged in series in a multi-stage configuration, in a multi-pass configuration, or a combination thereof. The first separate pump laser beam 105 and the second separate pump laser beam 107 are simultaneously delivered to both the seed laser 110 and the amplifier assembly 120 for automatic time synchronization of the seed laser and the amplifier assembly in an optical manner.

[0034] Additionally, the system 100 may further include pump splitting optics such as a beam splitter 104 , one or more turning mirrors 106 at the pump wavelength, and an isolator 108 interposed between the seed laser 110 and the amplifier assembly 120 . Figure 1 A typical all-passive high energy laser system 100 is shown having an amplifier assembly 120 optically synchronized with a single pump laser source 102. For practical reasons, for the multi-stage amplification assembly, a two-stage or three-stage amplifier may be used. Pump Laser

[0035] In an embodiment, a high energy pulsed laser is used to provide a common pump laser source 102 to pump the disclosed high energy (joule level) sub-nanosecond laser system 100 with a multi-stage / multi-pass amplifier. More specifically, the pump laser source 102 can simultaneously pump the seed laser 110 and each individual amplifier in the amplifier assembly 120, thereby achieving automatic synchronization of the passively Q-switched seed laser 110 with all amplifiers.

[0036] The pump laser source 102 may be operable to generate a pump laser beam 103 having a pump wavelength, which is at a certain pump energy and pulsed with a pump pulse duration. At the pump wavelength, the seed laser 110 and the gain medium 115 in the amplifier may absorb a large amount of pump energy. In various embodiments, for a neodymium (Nd) doped gain medium, the pump wavelength may range from about 730 nm to about 900 nm. The selection of the pump wavelength depends on several factors, such as a sufficiently high absorptivity of the gain medium, an available pump source, and considerations for reducing quantum defects. In at least one example, the pump wavelength may be about 750 nm. For efficient pumping, the pump pulse duration may be selected to be comparable to the fluorescence lifetime of the gain medium in the seed and amplifier. In some embodiments using a Nd doped gain medium, the pump pulse duration may be about 200 μs to about 500 μs. In at least one example, the pump pulse duration may be about 250 μs. The pump energy of the pump laser source 102 can be high enough to achieve passive Q-switching of the seed laser 110 and to supply sufficient energy storage in the gain medium in each amplifier stage, thereby achieving efficient amplification. In various embodiments, the pump energy can range from about 50 mJ to about 10 J. For example, the pump laser source emits a pump laser beam pulse having a pump energy greater than or equal to 1 J, greater than or equal to 2 J, greater than or equal to 3 J, greater than or equal to 4 J, greater than or equal to 5 J, greater than or equal to 6 J, greater than or equal to 7 J, greater than or equal to 8 J, or less than or equal to 10 J. In at least one example, the pump energy can be about 8 J.

[0037] In one example, the pump laser source 102 can be a flashlamp-pumped chrysoberyl laser emitting a pulsed laser of about 753 nm. In other examples, the gain medium for the seed laser or amplifier can include a neodymium-doped crystal or ceramic material. For neodymium-doped crystals or ceramic materials (i.e., yttrium aluminum garnet (YAG), yttrium aluminum perovskite (YAP), or yttrium lithium fluoride (YLF)), their lifetime is about 230 μs-500 μs, which gives a pump pulse duration that is roughly in the same range. For a Joule-level MOPA laser system based on Nd:YAG, a pump energy of about 8 J may be required.

[0038] In some embodiments, the pump laser source 102 may be fiber coupled, or free space propagated to the disclosed MOPA system. Passively Q-switched seed laser

[0039] In an embodiment, the passively Q-switched seed laser 110 may include a cavity including a gain medium 115 and a passive attenuator (eg, a saturable absorber 116).

[0040] In some embodiments, the passively Q-switched seed laser 110 may further include a pair of laser mirrors (e.g., a high reflector 113 and an output coupler 114) to form a laser resonator. The passively Q-switched seed laser 110 may further include an attenuator 111 for adjusting the pump energy and one or more pump beam shaping lenses 112 for producing an appropriate pump spot size in the gain medium. The attenuator 111 is positioned in the split pump beam path 105 before the pump beam enters the passively Q-switched laser resonator. For example, Figure 2 It is shown that the passively Q-switched seed laser 110 cavity can be formed by a high reflector laser mirror 113 and an output coupler laser mirror 114, with a gain medium 115 and a saturable absorber 116 in between. Unlike actively Q-switched lasers, there is no active Q-switching mechanism (i.e., acousto-optic or electro-optic) in a passively Q-switched laser resonator that requires an external electronic driver. Instead, Q-switching is achieved by a passive attenuator / optical device (e.g., saturable absorber 116) that acts as a fast-switching optical shutter. Passive Q-switching can provide better advantages to generate shorter pulses (i.e., sub-nanoseconds) compared to active Q-switching because the physical size of the saturable absorber is smaller and the switching time is faster than its compartmentalized, active counterpart. In addition, highly doped laser media are often used to reduce the thickness of the gain material, resulting in a shorter cavity length. In some embodiments, the exit surface of the gain medium can be coated with a high reflective coating at the pump wavelength to achieve a double-pass pumping geometry, thereby further reducing the gain medium length, resulting in an even shorter cavity length. The passively Q-switched short cavity seed laser 110 is arranged as a linear cavity to achieve compactness for generating sub-nanosecond laser pulses. In various embodiments, the passively Q-switched seed laser cavity can have a length of less than 10 mm, less than 8 mm, less than 6 mm, or less than 4 mm.

[0041] In an embodiment, the gain medium 115 and the passive attenuator 116 can be bonded together to form a monolithic structure. The front surface of the gain medium 115 can be coated with a highly reflective coating, and the back surface of the passive attenuator 116 can be coated with a partially reflective coating.

[0042] Typically, such as Figure 1As seen in FIG. 1 , a small amount of pump energy can be separated from the pump laser beam 103 by a beam splitter 104 to produce a first split pump laser beam 105. A second split pump laser beam 107 having the majority of the energy can be delivered to an amplifier assembly 120. For example, the pump laser beam 103 can be separated into 10% or less of the pump laser beam 103 energy directed to the seed laser 110 as a split pump laser beam 105, and 90% or more of the pump laser beam 103 energy directed to the amplifier assembly 120 as a split pump laser beam 107. In some embodiments, the split pump laser beam 105 is deflected by a mirror 106 to direct it to the seed laser 110. The beam splitter 104 can be any suitable beam splitter, such as, for example, a cube beam splitter, a partial reflector, a high refractive index plate, and a fiber connector. In an exemplary embodiment, the beam splitter 104 can be an uncoated sapphire plate or window.

[0043] Return to reference Figure 2 , the separated pump laser beam 105 can be received by the seed laser 110 and can pass through an attenuator 111 to adjust the pump energy to the seed cavity, which is followed by one or more pump beam shaping lenses 112 to provide an appropriate pump spot size in the gain medium 115. The attenuator 111 can be a variable neutral density filter or a rotating polarizer cube. The attenuator is used to adjust the Q-switched pulse time delay relative to the start of the pump laser pulse.

[0044] The seed laser beam 109 emitted from the seed laser 110 may have an energy of about several hundred μJ to about 20 mJ. The seed laser beam may be a sub-nanosecond laser pulse with a pulse duration as short as about 50 ps or 100 ps. The seed laser beam may have a seed wavelength in a range from about 1 μm to about 1.1 μm.

[0045] In some embodiments, a fast photodetector 117 can be placed near or in the seed laser 110 to monitor the Q-switched pulses and their time delays. Once the Q-switched pulses are detected, the photodetector 117 can provide a feedback signal to the pump laser source 102 and trigger the pump laser source 102 to shut down to prevent double or multiple pulses. In some examples, the photodetector 117 can communicate with a control system for the pump laser source 102. The communication can be wireless.

[0046] Several factors may affect the Q-switched pulse energy. These factors include the pump spot size in the gain medium 115, the initial transmittance of the saturable absorber 116, and the reflectivity of the output coupler laser mirror 114. In one example, the seed laser 110 may be a Cr 4+:YAG as a passive Q-switched chrysoberyl laser pumped Nd:YAG laser. When the pump pulse is about 50mJ and ~250μs and the laser cavity parameters (i.e., cavity length, pump spot size, initial transmittance of Cr4+:YAG and reflectivity of output coupler) are appropriate, the Q-switched Nd:YAG short cavity laser can generate millijoule sub-nanosecond laser pulses with a pulse duration as short as about 100ps. In another example, the laser medium can be Nd:YAP or Nd:YLF. Multi-stage amplifier assembly

[0047] In an embodiment, one or more amplifiers of the amplifier assembly 120 can be arranged in a multi-stage configuration including a first stage and a second stage. The amplifier assembly 120 can further include a seed laser beam shaping lens 121 and a second pump beam splitter 122, which is operable to split a portion of the second split pump laser beam 107 to pump a first amplifier 126 in the first stage, while the remaining portion of the second split pump laser beam 107 is directed to a second amplifier 128 in the second stage. In some embodiments, the amplifier assembly 120 can further include one or more dichroic mirrors 124 and 131 to combine the pump beam and the seed beam / pre-amplified seed beam.

[0048] Return to reference Figure 1 , pulses of the sub-nanosecond seed laser beam 109 may propagate through an isolator 108 (e.g., a Faraday isolator) before being sent to the multi-stage amplifier assembly 120 for amplification. The use of the isolator 108 may prevent any feedback from the amplifier assembly 120 from being sent back to the seed laser 110. If feedback from the amplifier assembly 120 is sent back to the seed laser 110, it may cause optical damage or Q-switching timing fluctuations. The multi-stage amplifier assembly 120 may also be operable to receive a majority of the pump energy (e.g., a split pump laser beam 107) from the same pump laser source 102 used to pump the seed laser 110.

[0049] Figures 3 to 6 1 shows an example of a fully passive sub-nanosecond MOPA system 100 with a dual-stage amplifier in the amplifier assembly 120. In some embodiments, the amplifier assembly 120 can have two inputs, namely, a seed laser beam 109 from after the isolator 108 and a separated pump laser beam 107 from after the beam splitter 104. The sub-nanosecond seed laser beam 109 generated by the seed laser 110 propagates through the optical isolator 108 and then enters the first stage of the amplifier assembly 120.

[0050] In an embodiment, the seed laser beam shaping lens 121 can be positioned in front of the amplifying laser medium of the first stage amplifier 126 to produce a preferred seed beam spot size and divergence to achieve better spatial overlap with the second separated pump laser beam 107 in the amplifying laser medium (i.e., the first stage amplifier 126). The remaining majority of the pump energy (i.e., the second separated pump laser beam 107) after being separated by the beam splitter 104 for pumping the seed laser 110 is used as a single pump source to excite the amplifier assembly 120. The amplifier assembly 120 can include an amplifier beam splitter 122 to separate a portion of the incident second separated pump laser beam 107 energy to pump the first stage, while the remaining pump energy is diverted to the second stage amplifier 128. The pump energy ratio of these two stages can be set to achieve the best final extraction efficiency. In terms of the pump laser beam propagation direction relative to the input seed laser, Figures 3 to 5 Three examples of configurations are shown in FIG.

[0051] Figure 3 A front-end pumping configuration is depicted, where the pump laser beam propagates forward through the amplifying medium (i.e., the first stage amplifier 126 and the second stage amplifier 128), respectively co-linear with the seed laser of the first stage and the amplified seed laser of the second stage leaving the first stage. A first pump beam shaping lens 123 can be used to shape the beam to achieve optimal spatial mode matching between the second separated pump laser beam 107 and the seed laser beam 109 in the amplifying medium of the first stage amplifier 126. A second pump beam shaping lens 130 can be introduced to provide mode matching between the pre-amplified seed laser for the second stage in the second stage amplifier 128 and the pump beam. A first dichroic mirror 124 and a second dichroic mirror 131 can be used to combine the pump beam with the seed laser beam of the first stage and the pre-amplified seed laser of the second stage, respectively. They are coated to be highly reflective at the pump wavelength and highly transmissive at the seed laser wavelength.

[0052] In some embodiments, an additional optical isolator 125 may be inserted between the first stage amplifier 126 and the second stage amplifier 128 to avoid any crosstalk between the two amplifiers causing undesirable optical damage and lower extraction efficiency. In order to prevent any residual pump energy from leaking through the amplification medium before being output from the system, the amplifier assembly may include one or more dichroic mirrors 133 and a beam dump 132 so that only the amplified sub-nanosecond laser beam is output as a single output.

[0053] In another embodiment, Figure 4Another pump laser configuration is shown in . In this embodiment, the pump beam enters the amplifier from the rear end surface of the amplifying medium so that the pump beam counter-propagates through the amplifying medium (i.e., the first stage amplifier 126 or the second stage amplifier 128) with the seed laser beam or the pre-amplified seed laser.

[0054] In some embodiments, the amplifying medium may also be pumped from both the front and back ends to provide a more uniform pump energy distribution and thus a uniform gain distribution across the length of the crystal / amplifying medium, e.g. Figure 5 As shown. For each amplification stage, the incident split pump laser beam 107 split by the amplifier beam splitter 122 is further split into two parts with the same or different energy ratios by the second beam splitter 134 or the third beam splitter 135. The pump beam shaping lenses 123 and 130 can be configured to produce appropriate spot sizes and beam divergences to achieve optimized mode matching in the forward and backward directions with the incident seed beam of the first stage. The same function is achieved by the pump beam shaping lenses 138 and 139 of the second stage. The dichroic mirrors 124 and 133 are operable to combine the pump beam with the seed laser beam of the first stage, and to combine the pump beam with the amplified seed laser beam of the second stage, respectively. Another set of dichroic mirrors 131 and 140 can be used to send another part of the pump beam to the rear surface of the amplification medium of the first stage amplifier 126 and the second stage amplifier 128, and to transmit the seed laser beam of the pre-amplifier and the amplified seed laser beam, respectively.

[0055] In an embodiment, the multi-stage amplifier component 120 may include more than 2 stages of amplifiers. In various embodiments, the amplifier component 120 may include 1, 2, 3, or 4 amplifiers. In at least one example, the amplifier component 120 may include three stages, the three stages including three amplifiers. As an example, Figure 6 A three-stage amplifier assembly 120 with a forward pumping configuration is shown. Pump beam splitters 122 and 134 for the amplifier can be used to separate the pump beam energy available to the amplifier assembly into three parts to pump three amplifiers, namely, a first stage amplifier 126, a second stage amplifier 128, and a third stage amplifier 142. Pump beam shaping lenses 123, 130, and 138 are positioned in the pump beam path to achieve mode matching of the pump beams of the three stages with their corresponding seed laser beams. The same function can be achieved using seed laser beam shaping lenses 121, 127, and 136 for the seed laser beam. Similar to the two-stage system, other pumping configurations (i.e., backward pumping and double-ended pumping) can also be associated with this configuration. Multi-pass amplification

[0056] Figure 7 and Figure 8 In a single stage ( Figure 7 ) or dual level ( Figure 8) in an example optical synchronized MOPA system with a multi-pass amplifier assembly and a backward pumping configuration. In some embodiments, the high energy laser system 200 includes a passively Q-switched short cavity seed laser 210, a multi-pass amplifier assembly 220, and a pump laser 202. In addition, the system can further include a pump beam splitting optical device 204, a steering mirror 206, and an isolator 208 inserted between the seed laser 210 and the amplifier assembly 220. The amplifier assembly 120 can include: one or more amplifiers 226, 236; one or more seed laser beam shaping lenses 221, 227; one or more pump beam shaping lenses 223, 235; polarization optics 222; one or more dichroic mirrors 224, 231; one or more steering mirrors 229, 230, 232; and a quarter wave plate 228. In an embodiment, the amplifier assembly 120 includes one amplifier and is arranged in a multi-pass configuration. Figure 7 A typical all-passive high energy laser system 200 is shown having a multi-pass amplifier assembly 220 optically synchronized with a single pump laser 202 .

[0057] Similar to the multi-stage amplifier assembly, the multi-pass amplifier assembly 220 receives the first separated pump laser beam 207 and the seed laser beam 209 after the isolator 208. In this configuration, only one laser amplification medium (e.g., amplifier 226) is used. The seed laser beam 209 is arranged to pass back and forth through the amplifier 226 multiple times before being emitted from the amplifier 226 to obtain efficient amplification. The seed laser beam 209 travels back and forth in the amplification medium colinearly or spatially separated. For a colinear multi-pass system, the control of the output beam relies on polarization differences. An example is Figure 7The collinear double-pass amplifier shown. The seed laser 210 and the isolator 208 are arranged in such a way that the seed laser beam 209 after the isolator 208 is P polarized. The polarization optical component 222 is operable to allow the P polarized seed laser to pass through it and propagate through the amplifier 226 as a first pass, and then be reflected by the dichroic mirror 224. The reflected amplified seed laser beam further passes through the quarter wave plate 228 and is reflected back by the mirror 232 (which can be flat or curved) in the exact opposite propagation direction. When the amplified seed laser beam passes through the quarter wave plate 228 for the second time, its polarization is turned 90 degrees and becomes an S polarized beam, which is once again redirected by the dichroic mirror 224 into the amplifier 226 as a second pass to obtain further amplification. After the second pass through the amplifying medium, the S polarized beam is reflected by the polarization optical device 222. It should be noted that the polarization optical device 222 can be a thin film polarizer or a polarization cube. A dichroic mirror 224 may be used as a beam combiner to transmit the pump beam and combine it with the reflected seed beam so that the two beams propagate co-linearly toward the amplifying medium. The multi-pass amplifier assembly also includes one or more pump beam steering mirrors 229 , 230 and a pump beam shaping lens 223 .

[0058] In some cases where further amplification is desired, an amplifier assembly 220 having a combined multi-pass and multi-stage amplifier is involved. For example, the amplifier assembly 220 may include two or more amplifiers arranged in a combined multi-pass and multi-stage configuration. In some embodiments, the first amplifier and / or the second amplifier is pumped from the front end or the back end of the amplifier medium. In some embodiments, the first amplifier and / or the second amplifier is pumped from both the front end and the back end to provide a uniform pump energy distribution. In other embodiments, the amplifier assembly 120 includes a dual-pass amplifier in the first stage followed by a single-pass amplifier in the second stage. Figure 8 An example of an amplifier assembly 220 is shown, which includes a double pass amplifier 226 as a first stage followed by a second stage amplifier 236. Similar to a typical two-stage amplifier system, this hybrid amplifier system uses a double pass amplifier to replace a typical single pass amplifier as the first stage. A common feature of all the configurations disclosed is that the pump beam for each stage or pass and the seed laser are derived from the same pump laser, which is necessary to achieve optical synchronization and fully passive operation of the laser system.

[0059] The above configurations are not exclusive but provided as examples. Other configurations for multi-stage / multi-pass MOPA systems with optical synchronization should be considered part of the present disclosure. Optical synchronization

[0060] The advantage of a sub-nanosecond laser system is that a common pump laser optically synchronizes the passively Q-switched laser with its multi-stage / multi-pass amplifier assembly. As an example, Fig. 9 The principle of how a two-stage amplifier assembly works synchronously is shown. The start of the pump laser pulse sets time zero for the clock of the entire system. As pumping proceeds, the gain of the seed laser gain medium and the two amplifiers begin to accumulate simultaneously. If no Q-switching occurs, all gain curves will reach a maximum and then deplete to zero simultaneously. The magnitude of the gain value for a given gain medium depends on its pump energy and doping concentration. The time required to reach the peak of the gain curve is determined by the fluorescence lifetime of the gain medium and other depletion mechanisms such as amplified spontaneous emission (ASE) or spontaneous lasing.

[0061] In the presence of a passive Q-switching mechanism in the seed laser, short Q-switched pulses can be generated when the stored gain value overcomes the cavity losses. The Q-switching delay is the time required for the gain of the seed gain medium to exceed the losses. In some embodiments, control of the amplified laser energy can be achieved by adjusting the Q-switching time delay of the seed laser while maintaining a constant pump energy for each amplifier stage to achieve a stable thermal distribution in the amplifying medium. The Q-switching delay time can be changed by adjusting the attenuation of the pump energy of the seed laser.

[0062] The sub-nanosecond Q-switched pulse serves as the end time point of the gain accumulation of the amplified gain medium. And this end time point can be considered to be roughly the same for all amplified media. Although the optical paths for each stage may differ by several meters, when compared on a scale of hundreds of microseconds set by the fluorescence time of the gain medium, it takes roughly the same time for the light to travel through each amplification stage. The gain stored in each amplification medium during the Q-switched delay time can be used for extraction. Therefore, synchronization can be achieved by a pump laser pulse, whose rising edge defines time zero and a passive Q-switched pulse sets the end time. In some embodiments, the same principles can be applied to multi-pass amplification and combined multi-pass and multi-stage amplification systems. Energy control by adjusting the Q-switching time delay

[0063] Most commonly, output energy regulation of MOPA systems is achieved primarily by adjusting the pump power / energy passed to the amplifier. However, this energy control scheme may encounter several problems. First, for MOPA systems that require a wide range of energy tunability, the pump power / energy passed to the amplifier must change dramatically from low to high. Therefore, thermal lensing and depolarization will vary significantly and cause problems for some applications that require stable beam polarization. Some examples are harmonic generation, pumping anisotropic laser media, polarization-sensitive measurements, etc. The second problem comes from the instability of the amplified laser energy at very low energy levels. Low output energy involves low pump energy. However, the most commonly used pump lasers can become less stable, and their energy fluctuates much more at very low energies than at higher energy levels. Therefore, large fluctuations in pump energy will directly translate into unstable energy of the amplified laser at the low end of the energy level. In addition, unstable pump energy will cause fluctuations in the Q-switched seed laser pulse delay relative to the start of the pump pulse, which will lead to further unstable output energy.

[0064] To overcome these problems, control of the pump energy to the seed rather than the pump energy to the amplifier can achieve energy control while maintaining a constant pump energy to the amplifier components. In this case, the pump energy to the amplifier is set to a level that can achieve stable operation. An example is to operate the pump at a maximum constant energy level to pump the amplifier.

[0065] In an embodiment, optical synchronization of the disclosed laser system can achieve energy control by adjusting the Q-switching time delay while maintaining the same pump energy for each amplifier stage. Figure 2 As shown in FIG. 1 , an attenuator is placed in the pump beam path of the seed laser to adjust the pump beam energy. When the pump beam energy to the seed laser is set to a lower value, more time is required to generate the Q-switched pulse, so the Q-switching delay is longer. Fig. 11B As shown in , due to optical synchronization, longer Q-switching delays will result in greater gain storage in the amplifying medium available for extraction, leading to higher amplified output energy. Fig.11A It was shown that lower output energies can be obtained by adjusting the Q-switching delay time to a short time with higher pump energy to the seed. Fig.11A and Fig. 11BEnergy tuning of the amplification by controlling the Q-switched seed laser pulse delay by adjusting the pump energy to the seed is demonstrated for a two-stage amplifier assembly. It should be noted that the gain profile in the amplifying medium remains unchanged due to the constant pump energy to the amplifier assembly, but the gain in the seed laser varies due to the change in the pump energy to the seed laser. The same principle can be applied to amplifier assemblies consisting of single-pass single-stage amplifiers, or multi-pass amplifiers, and combinations of multiple and multi-pass amplifiers.

[0066] It will be understood by those skilled in the art that the present disclosure is not limited to what is specifically shown and described above. Rather, the scope of the laser system includes combinations and sub-combinations of the various features described above, as well as modifications and variations thereof that would occur to those skilled in the art upon reading the foregoing description and that are not in the prior art.

[0067] The disclosure shown and described above is merely an example. Although many features and advantages of the present technology, as well as details of the structure and function of the present disclosure have been set forth in the foregoing description, the present disclosure is merely illustrative and may be varied in detail, particularly in shape, size, and arrangement of parts, within the principles of the present disclosure and within the full range indicated by the broad general meaning of the terms used in the appended claims. It will be understood, therefore, that the above examples may be modified within the scope of the appended claims.

[0068] Many examples are provided herein to enhance the understanding of the present disclosure. A specific set of statements is provided below.

[0069] Statement 1. A sub-nanosecond laser system comprising: a pump laser source operable to generate a pump laser beam having a pump wavelength; a first pump beam splitter operable to receive the pump laser beam and to split the pump laser beam into at least a first split pump laser beam and a second split pump laser beam; a passively Q-switched seed laser operable to receive the first split pump laser beam and to generate a seed laser beam, the passively Q-switched seed laser comprising a cavity comprising a gain medium and a passive attenuator; and an amplifier assembly operable to receive the second split pump laser beam and the seed laser beam and to generate an amplified laser beam, the amplifier assembly comprising one or more amplifiers, wherein the one or more amplifiers are arranged in series in a multi-stage configuration, in a multi-pass configuration, or a combination thereof, wherein the first split pump laser beam and the second split pump laser beam are simultaneously delivered to both the seed laser and the amplifier assembly for optically automatically time synchronizing the seed laser and the amplifier assembly.

[0070] Statement 2. The system of statement 1, wherein the one or more amplifiers are arranged in a multi-stage configuration including a first stage and a second stage, and wherein the amplifier assembly further includes a seed laser beam shaping lens and a second pump beam splitter, the second pump beam splitter being operable to split a portion of the second split pump laser beam to pump a first amplifier in the first stage, while a remaining portion of the second split pump laser beam is directed to a second amplifier in the second stage.

[0071] Statement 3. The system of statement 2 wherein the amplifier assembly further comprises one or more dichroic mirrors.

[0072] Statement 4. The system of statement 2, wherein the pump laser beam enters the first amplifier and / or the second amplifier from a front end surface of the amplifier such that the pump laser beam propagates through the first amplifier or the second amplifier colinearly with the seed laser beam or the pre-amplified seed laser beam.

[0073] Statement 5. The system of statement 2, wherein the pump laser beam enters the first amplifier and / or the second amplifier from a rear end surface of the amplifier such that the pump laser beam propagates through the first amplifier or the second amplifier in a counter-propagation manner with the seed laser beam or the pre-amplified seed laser beam.

[0074] Statement 6. The system of statement 5, wherein the first amplifier and / or the second amplifier is pumped from both the front surface and the back surface to provide a uniform pump energy distribution across the length of the amplifying medium.

[0075] Statement 7. The system of statement 2 wherein the amplifier assembly further comprises a third stage, the third stage comprising a third amplifier.

[0076] Statement 8. The system of statement 1 wherein the amplifier assembly comprises one amplifier and is arranged in a multi-pass configuration.

[0077] Statement 9. The system of statement 8, wherein the seed laser beam is arranged to pass back and forth through the amplifier multiple times before being emitted from the amplifier to achieve efficient amplification.

[0078] Statement 10. The system of statement 9 wherein the seed laser beam travels back and forth in the amplifier either co-linearly or spatially separated.

[0079] Statement 11. The system of statement 1 wherein the amplifier assembly comprises two or more amplifiers arranged in a combined multi-pass and multi-stage configuration.

[0080] Statement 12. The system of statement 11 wherein the amplifier assembly includes a two-pass amplifier in a first stage followed by a second stage amplifier.

[0081] Statement 13. The system of statement 1 wherein the passively Q-switched seed laser cavity has a length of less than 10 mm.

[0082] Statement 14. The system of statement 1 wherein the seed laser is operable to generate millijoule-level laser pulses and a pulse duration of 100 ps or less.

[0083] Statement 15. The system of statement 1 further comprising one or more isolators positioned between the seed laser and the amplifier assembly.

[0084] Statement 16. The system of statement 1 wherein the amplifier assembly further comprises an additional isolator between two adjacent stages.

[0085] Statement 17. The system of statement 1 wherein the passive attenuator is a saturable absorber.

[0086] Statement 18. The system of statement 1 wherein the passively Q-switched seed laser further comprises a pair of laser mirrors for forming a laser resonator.

[0087] Statement 19. The system of statement 18 wherein the pair of laser mirrors comprises a high reflector and an output coupler.

[0088] Statement 20. The system of statement 1 wherein the passively Q-switched seed laser comprises a separate gain medium and a passive attenuator.

[0089] Statement 21. The system of statement 1 wherein the passively Q-switched seed laser comprises a gain medium and a passive attenuator coupled together to form a monolithic structure.

[0090] Statement 22. The system of statement 21 wherein a front surface of the gain medium is coated with a highly reflective coating and a rear surface of the passive attenuator is coated with a partially reflective coating.

[0091] Statement 23. The system of statement 1 wherein the passively Q-switched seed laser further comprises a pump beam shaping lens and an attenuator for adjusting pump energy.

[0092] Statement 24. The system of statement 23 wherein the attenuator comprises a variable neutral density filter or a rotating polarizer cube.

[0093] Statement 25. The system of statement 1 wherein the passively Q-switched seed laser further comprises a photodetector operable to: monitor Q-switched pulses from the seed laser and their time delays; provide a feedback signal to the pump laser source; and trigger the pump laser source to shut down to prevent double or multiple pulses.

[0094] Statement 26. The system of statement 1 wherein the pump laser source emits pump laser beam pulses having a pump energy greater than 1J.

[0095] Statement 27. The system of statement 26 wherein the pump energy is sufficiently high to achieve passive Q-switching of the seed laser and to supply sufficient energy storage in the gain medium in each amplifier to achieve efficient amplification.

[0096] Statement 28. The system of statement 26 wherein the pump laser beam pulses have a pulse duration of approximately 100 μs-500 μs.

[0097] Statement 29. The system of statement 1 wherein the gain medium for the seed laser or the amplifier comprises a neodymium-doped crystal or a ceramic material.

[0098] Statement 30. The system of statement 29 wherein the gain medium is selected from yttrium aluminum garnet (YAG), yttrium aluminum perovskite (YAP), or yttrium lithium fluoride (YLF).

[0099] Statement 31. The system of statement 1 wherein the pump laser source is a flash lamp pumped chrysoberyl laser emitting a pulsed laser beam at approximately 753 nm.

[0100] Statement 32. The system of statement 1 wherein control of the amplified laser energy is achieved by adjusting a time delay of the seed laser while maintaining a constant pump energy for each amplifier stage and achieving a stable thermal profile in the amplifying medium.

[0101] Statement 33. The system of statement 32 wherein the delay time is varied by adjusting the attenuation of pump energy to the seed laser.

Claims

1. A sub-nanosecond laser system, comprising: a pump laser source operable to generate a pump laser beam having a pump wavelength; a first pump beam splitter operable to receive the pump laser beam and split the pump laser beam into at least a first split pump laser beam and a second split pump laser beam; a passively Q-switched seed laser operable to receive the first split pump laser beam and generate a seed laser beam, the passively Q-switched seed laser comprising a cavity including a gain medium and a passive attenuator; as well as an amplifier assembly operable to receive the second separate pump laser beam and the seed laser beam and produce an amplified laser beam, the amplifier assembly comprising one or more amplifiers, wherein the one or more amplifiers are arranged in series in a multi-stage configuration, in a multi-pass configuration, or a combination thereof, wherein the first separate pump laser beam and the second separate pump laser beam are simultaneously delivered to both the seed laser and the amplifier assembly for automatically time synchronizing the seed laser and the amplifier assembly optically.

2. The system according to claim 1, wherein: The one or more amplifiers are arranged in a multi-stage configuration including a first stage and a second stage, and wherein the amplifier assembly further includes a seed laser beam shaping lens and a second pump beam splitter, the second pump beam splitter being operable to split a portion of the second split pump laser beam to pump a first amplifier in the first stage, while a remaining portion of the second split pump laser beam is directed to a second amplifier in the second stage.

3. The system according to claim 2, wherein: The amplifier assembly further includes one or more dichroic mirrors.

4. The system according to claim 2, wherein: The pump laser beam enters the first amplifier and / or the second amplifier from a front end surface of the first amplifier or the second amplifier, so that the pump laser beam and the seed laser beam or the pre-amplified seed laser beam propagate through the first amplifier or the second amplifier in a colinear manner.

5. The system according to claim 2, wherein: The pump laser beam enters the first amplifier and / or the second amplifier from a rear end surface of the first amplifier or the second amplifier, so that the pump laser beam and the seed laser beam or the pre-amplified seed laser beam counter-propagate through the first amplifier or the second amplifier.

6. The system according to claim 5, wherein: The first amplifier and / or the second amplifier are pumped from both the front surface and the back surface to provide a uniform pump energy distribution across the length of the amplifying medium.

7. The system according to claim 2, wherein: The amplifier assembly further comprises a third stage comprising a third amplifier.

8. The system according to claim 1, wherein: The amplifier assembly includes an amplifier and is arranged in a multi-pass configuration.

9. The system according to claim 8, wherein: The seed laser beam is arranged to pass back and forth through the amplifier multiple times before being emitted from the amplifier to obtain efficient amplification.

10. The system according to claim 9, wherein: The seed laser beams travel back and forth in the amplifier either collinearly or spatially separated.

11. The system according to claim 1, wherein: The amplifier assembly includes two or more amplifiers arranged in a combined multi-pass and multi-stage configuration.

12. The system according to claim 11, wherein: The amplifier assembly comprises a two-pass amplifier in a first stage followed by a second stage amplifier.

13. The system of claim 1, wherein: The passively Q-switched seed laser cavity has a length of less than 10 mm.

14. The system of claim 1, wherein: The seed laser is operable to generate millijoule-level laser pulses with a pulse duration of 100 ps or less.

15. The system of claim 1, further comprising one or more isolators positioned between the seed laser and the amplifier component.

16. The system of claim 1, wherein: The amplifier assembly further comprises an additional isolator between two adjacent stages.

17. The system of claim 1, wherein: The passive attenuator is a saturable absorber.

18. The system of claim 1, wherein: The passively Q-switched seed laser further includes a pair of laser mirrors for forming a laser resonator.

19. The system of claim 18, wherein: The pair of laser mirrors includes a high reflector and an output coupler.

20. The system of claim 1, wherein: The passively Q-switched seed laser includes a separate gain medium and a separate passive attenuator.

21. The system of claim 1, wherein: The gain medium and the passive attenuator are coupled together to form a monolithic structure.

22. The system of claim 21, wherein: The front surface of the gain medium is coated with a high reflective coating, and the rear surface of the passive attenuator is coated with a partially reflective coating.

23. The system of claim 1, wherein: The passively Q-switched seed laser further includes an attenuator and a pump beam shaping lens, wherein the attenuator is positioned in the pump beam path before entering the laser resonator for adjusting the pump energy.

24. The system of claim 23, wherein: The attenuator includes a variable neutral density filter or a rotating polarizer cube.

25. The system of claim 1, wherein: The passively Q-switched seed laser further comprises a photodetector operable to: monitoring the Q-switched pulses from the seed laser and their time delays; providing a feedback signal to the pump laser source; and Trigger the pump laser source off to prevent double pulsing or multiple pulsing.

26. The system of claim 1, wherein: The pump laser source emits a pump laser beam pulse having a pump energy greater than 1J.

27. The system of claim 26, wherein: The pump energy is high enough to achieve passive Q-switching of the seed laser and to supply sufficient energy storage in the gain medium in each amplifier to achieve efficient amplification.

28. The system of claim 26, wherein: The pump laser beam pulse has a pulse duration of about 100 μs-500 μs.

29. The system of claim 1, wherein: The gain medium for the seed laser or the amplifier includes a neodymium-doped crystal or a ceramic material.

30. The system of claim 29, wherein: The gain medium is selected from yttrium aluminum garnet (YAG), yttrium aluminum perovskite (YAP), or yttrium lithium fluoride (YLF).

31. The system of claim 1, wherein: The pump laser source is a flash lamp pumped chrysoberyl laser that emits a pulsed laser beam of about 753 nm.

32. The system of claim 1, wherein: Control of the amplified laser energy is achieved by adjusting the time delay of the seed laser while maintaining a constant pump energy for each amplifier stage and achieving a stable thermal distribution in the amplifying medium.

33. The system of claim 32, wherein: The delay time is varied by adjusting the attenuation of the pump energy to the seed laser.

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