1064 nm all-solid-state laser based on beam homogenization and circular polarization amplification

Abstract

The application belongs to the technical field of laser, and proposes a 1064nm all-solid-state laser based on beam homogenization and circular polarization amplification, which comprises an oscillator, a pre-amplifier, a first main amplifier, a second main amplifier, a third main amplifier and a fourth main amplifier arranged along an optical path in sequence, the beam homogenization technology is introduced to control and optimize the laser beam after the second main amplifier, the circular polarization amplification technology is used to optimize the energy amplification process of the third main amplifier and the fourth main amplifier, and the high-stability compact high-energy 1064nm laser output is completed without using a spatial filter and a stimulated Brillouin scattering phase conjugation mirror.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lasers, in particular to a 1064 nm all-solid-state laser based on beam homogenization and circular polarization amplification. BACKGROUND

[0002] The statements in this section merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] With the development of laser technology, it has been widely used in many fields such as industrial processing, medical devices, scientific research, etc., especially in precision machining, illumination detection, identification tracking, etc., and the demand for high repetition frequency, high beam quality, large energy laser is becoming more and more urgent. However, it is a technical bottleneck to achieve single pulse energy output of joule level and above while maintaining high beam quality under high repetition frequency conditions. At present, most large energy lasers usually face the following problems:

[0004] (1) Trade-off between beam quality and single pulse energy output: In the process of improving the output energy of traditional lasers, the beam quality is often degraded, such as the increase of beam divergence angle, serious spot distortion, etc., which seriously affects the actual application effect of laser; In order to maintain high efficiency and high precision in long-distance ranging, active detection and other fields, the laser output by the laser needs to have good beam quality and spot shape, and be able to maintain stable output under high repetition frequency;

[0005] (2) System stability: In the process of long-time running, the output power of the laser is easily affected by environmental factors, aging of components, etc., resulting in large energy fluctuation and affecting the application effect; Especially in the fields of industry and scientific research, the power stability and the consistency of the spot shape of the laser are crucial; For example, in laser processing, power fluctuation will directly affect the cutting or welding quality; In laser ranging, unstable spot shape will reduce the measurement accuracy;

[0006] (3) Reliability and maintainability: The existing laser usually has complex structure, and often uses spatial filter and stimulated Brillouin scattering phase conjugation mirror (SBS-PCM) and other optical field improvement elements in the optical path, but they are easy to be damaged, not only difficult to maintain, but also easy to be damaged during transportation and use; Especially in high-vibration environments such as vehicle-mounted and airborne, the laser is difficult to maintain long-term stable working state; In addition, the optical path debugging of the laser requires high technical level, which increases the difficulty of use and maintenance;

[0007] (4) Limited scalability: The design of the laser often stops at meeting the current use demand, lacks forward-looking scalability, and cannot further improve the energy and power output based on the existing optical path, which limits its potential in higher energy application fields. SUMMARY

[0008] In order to overcome the shortcomings of the prior art on high repetition frequency, high beam quality, joule-level and above single pulse energy laser, the application provides a compact, high repetition frequency, high beam quality, joule-level single pulse energy 1064nm all-solid-state laser based on beam homogenization technology and circular polarization amplification technology, which uses a near-diffraction-limited fundamental mode seed light output by an all-solid-state Gauss mirror plano-convex cavity oscillator, further amplifies the single pulse energy on the basis of pre-amplification (almost without deterioration of spot shape and beam quality), and then introduces the beam homogenization technology after one-stage and two-stage main amplification to control and optimize the laser beam, without using complex devices such as spatial filters and stimulated Brillouin scattering phase conjugation mirrors (SBS-PCM), and finally uses the circular polarization amplification technology to optimize the large energy amplification process at the three-stage and four-stage main amplification, so as to realize high repetition frequency, high beam quality and joule-level single pulse energy laser output.

[0009] In order to achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0010] In a first aspect, the application provides a 1064nm all-solid-state laser based on beam homogenization and circular polarization amplification.

[0011] A 1064nm all-solid-state laser based on beam homogenization and circular polarization amplification, comprising an oscillator, a pre-amplifier, a one-stage main amplifier, a two-stage main amplifier, a three-stage main amplifier and a four-stage main amplifier arranged in sequence along the optical path, the oscillator is used to provide a fundamental mode seed light, and the pre-amplifier is used to amplify the single pulse energy of the fundamental mode seed light output by the oscillator;

[0012] The one-stage main amplifier, the two-stage main amplifier, the three-stage main amplifier and the four-stage main amplifier sequentially amplify the seed light amplified by the pre-amplifier and output 1064nm laser, and a beam homogenizer is arranged on the optical path between the two-stage main amplifier and the three-stage main amplifier;

[0013] In the three-stage main amplifier and the four-stage main amplifier, the horizontal polarization state of the light beam is first converted into a circular polarization state, and the light in the circular polarization state is amplified and then converted back to a horizontal polarization state.

[0014] In an implementation form of the first aspect of the application, the oscillator comprises, in sequence along the optical path, a full reflection mirror, an electro-optic Q-switch KD * P crystal, a first 1064nm λ / 4 wave plate, a 1064nm polarization beam splitter prism, a 3mm Nd:YAG crystal rod oscillation side pump module and an output mirror.

[0015] In an implementation form of the first aspect of the present application, the pre-amplifier comprises, in sequence along the light path, a pre-amplification beam-shaping lens group, a first optical isolator, a front 1064 nm λ / 2 wave plate, a first 1064 nm λ / 2 and λ / 4 wave plate, a pre-amplification side-pumped module of a 3 mm Nd:YAG crystal rod, and a first compensation lens.

[0016] In an implementation form of the first aspect of the present application, the first-stage main amplifier comprises, in sequence along the light path, a first-stage main amplification beam-shaping lens group, a second optical isolator, a front 1064 nm λ / 2 wave plate, a second 1064 nm λ / 2 and λ / 4 wave plate, a first-stage side-pumped module I of a 5 mm Nd:YAG crystal rod, a second compensation lens, a first quartz rotator, a first-stage side-pumped module II of a 5 mm Nd:YAG crystal rod, and a third compensation lens.

[0017] The second-stage main amplifier comprises, in sequence along the light path, a second-stage main amplification beam-shaping lens group, a third optical isolator, a front 1064 nm λ / 2 wave plate, a third 1064 nm λ / 2 and λ / 4 wave plate, a second-stage side-pumped module I of an 8 mm Nd:YAG crystal rod, a fourth compensation lens, a second quartz rotator, a second-stage side-pumped module II of an 8 mm Nd:YAG crystal rod, and a fifth compensation lens.

[0018] The third-stage main amplifier comprises, in sequence along the light path, a third-stage main amplification beam-shaping lens group, a fourth optical isolator, a front 1064 nm λ / 2 wave plate, a fourth 1064 nm λ / 2 and λ / 4 wave plate, a third-stage side-pumped module I of a 12 mm Nd:YAG crystal rod, a sixth compensation lens, a third quartz rotator, a third-stage side-pumped module II of a 12 mm Nd:YAG crystal rod, a seventh compensation lens, and a second 1064 nm λ / 4 wave plate.

[0019] The fourth-stage main amplifier comprises, in sequence along the light path, a fifth optical isolator, a front 1064 nm λ / 2 wave plate, a fifth 1064 nm λ / 2 and λ / 4 wave plate, a fourth-stage side-pumped module I of a 12 mm Nd:YAG crystal rod, an eighth compensation lens, a fourth quartz rotator, a fourth-stage side-pumped module II of a 12 mm Nd:YAG crystal rod, a ninth compensation lens, and a third 1064 nm λ / 4 wave plate.

[0020] As a further limitation of the first aspect of the present application, the first-stage main amplification beam-shaping lens group is a spherical concave-convex lens group for expanding and collimating a Gaussian light beam by a factor of 2, the second-stage main amplification beam-shaping lens group is a spherical concave-convex lens group for expanding and collimating a Gaussian light beam by a factor of 1.5, and the third-stage main amplification beam-shaping lens group is a spherical concave-convex lens group for expanding and collimating a Gaussian light beam by a factor of 1.75.

[0021] As a further limitation of the first aspect of the application, the first, second, third and fourth quartz rotators each use the birefringence effect of a quartz crystal to rotate the polarization of the laser light by 90 degrees.

[0022] In an implementation form of the first aspect of the application, a polarization splitting switch is arranged in the optical path between the first main amplifier and the second main amplifier.

[0023] In an implementation form of the first aspect of the application, the laser light output by the second main amplifier is first processed by a depolarization splitter and then by a beam homogenizer.

[0024] In an implementation form of the first aspect of the application, the beam homogenizer comprises, in sequence along the optical path, a 1064 nm λ / 2 wave plate, a 1064 nm beam homogenizer plate (effective action diameter of 8 mm) and a 1064 nm polarization splitting prism.

[0025] In a second aspect, the application provides a method for generating 1064 nm laser light.

[0026] A method for generating 1064 nm laser light using the 1064 nm all-solid-state laser based on beam homogenization and circularly polarized amplification according to the first aspect of the application comprises the following processes:

[0027] Starting the oscillator and outputting the fundamental mode seed light from the oscillator;

[0028] Inputting the fundamental mode seed light output by the oscillator into the pre-amplifier and amplifying the single pulse energy of the fundamental mode seed light by the pre-amplifier;

[0029] Inputting the seed light amplified by the pre-amplifier into the first main amplifier and the second main amplifier in sequence and sequentially amplifying the energy by the first main amplifier and the second main amplifier;

[0030] Introducing the laser light amplified by the second main amplifier into the beam homogenizer and homogenizing the laser beam by the beam homogenizer;

[0031] Inputting the homogenized laser light into the third main amplifier, converting the horizontal polarization state of the beam into a circularly polarized state by the λ / 4 wave plate before the third main amplifier, amplifying the energy of the circularly polarized laser light, and then converting it back to a horizontal polarization state by the λ / 4 wave plate;

[0032] Inputting the laser light processed by the third main amplifier into the fourth main amplifier, converting the horizontal polarization state of the beam into a circularly polarized state by the λ / 4 wave plate before the fourth main amplifier, amplifying the energy of the circularly polarized laser light, and then converting it back to a horizontal polarization state by the λ / 4 wave plate, and finally outputting the 1064 nm laser light.

[0033] Compared with the prior art, the application has the beneficial effects that:

[0034] The application introduces a beam homogenization process after the second main amplification to control and optimize the high-energy laser beam. Generally, when the single-pulse energy amplification of the high-repetition-rate high-energy laser amplification process reaches a certain degree, a certain strong core and peripheral distortion will be generated, especially the strong core, which further aggravates the self-focusing effect and leads to serious spot distortion in subsequent amplification, even hollow, and also easily damages the subsequent amplification crystal rod, and the process will be aggravated with further subsequent amplification, leading to rapid deterioration of beam quality and spot. Finally, even if a large single-pulse energy output is achieved, the poor beam quality and extremely deformed spot have lost their application significance. The application introduces a beam homogenization technology after the second main amplification. The beam homogenization technology can filter out the dark and weak distortion part of the outermost part of the spot while appropriately filtering out the core intensity of the spot, so as to obtain a nearly ideal laser beam, and then improve the amplification efficiency and spot shape of the third and fourth main amplifications under high-energy amplification, and well control the beam quality.

[0035] The third and fourth main amplifiers of the application adopt a circular polarization amplification process, which can effectively reduce the self-focusing intensity in high-energy pulse amplification, and in combination with the de-strong core process of the beam homogenization technology, the beam quality and spot deterioration caused by thermal distortion can be well controlled and optimized. In the circular polarization amplification process, the electric field vector rotates with time, equivalent omnidirectional excitation, weak polarization dependence, approximately isotropic amplification, and the electric field is averaged, the nonlinearity accumulation is suppressed, and the fault tolerance to polarization drift is large, which can obviously weaken the thermal birefringence and extract energy more uniformly. Therefore, in the further amplification of the third and fourth high-energy signals, the circular polarization amplification can more effectively control the deterioration to realize high-quality spot laser output under high beam quality.

[0036] The application successfully balances the demand for high repetition frequency and high beam quality, so that the laser can maintain good beam quality and laser spot at high repetition frequency, and is suitable for high-demand application scenarios such as precision measurement and long-distance detection. Through the technical design of oscillation and amplification, especially the beam homogenization process and the circular polarization amplification process, the application realizes the maintenance of good spot shape when stable output of joule-level and above single-pulse energy laser is realized.

[0037] The application has the advantages of full solid-state side pump module, light beam homogenization technology and circular polarization amplification technology, removes the commonly used spatial filter and stimulated Brillouin scattering phase conjugation mirror (SBS-PCM) and other vulnerable devices in system design, so that the whole system is more stable and reliable, the modular design not only simplifies the maintenance process, but also can maintain high stability in high vibration environment (such as vehicle-mounted and airborne), and is very suitable for application on mobile platform; the application can increase the output power to 900W, the single pulse energy to 3.0J, and the beam quality factor M 2 2 BRIEF DESCRIPTION OF DRAWINGS

[0038] The drawings constituting a part of the specification of the application are used to provide further understanding of the application, the illustrative embodiments of the application and the description thereof are used to explain the application, and do not constitute improper limitation on the application.

[0039] Figure 1 The structure schematic diagram of the 1064nm full solid-state laser based on light beam homogenization and circular polarization amplification provided for an exemplary embodiment of the application is shown in the following figure:

[0040] Figure 2 The spectrum and spectral line width of the oscillator output laser are shown in the following figure, the center wavelength is 1064.4nm, and the full width at half maximum is 0.06nm;

[0041] Figure 3 The average power and single pulse energy of the output laser when the pump current is increased from 20A to 80A in the two modules of the four-stage main amplifier of the laser provided for an exemplary embodiment of the application are shown in the following figure, wherein the four-stage LD I amplification average power represents the amplification average power of the four-stage side pump module I of the 12mm Nd:YAG crystal rod of the four-stage amplifier, the four-stage LD II amplification average power represents the amplification average power of the four-stage side pump module II of the 12mm Nd:YAG crystal rod of the four-stage amplifier, the four-stage LD I amplification single pulse energy represents the amplification single pulse energy of the four-stage side pump module I of the 12mm Nd:YAG crystal rod of the four-stage amplifier, and the four-stage LD II amplification single pulse energy represents the amplification single pulse energy of the four-stage side pump module II of the 12mm Nd:YAG crystal rod of the four-stage amplifier;

[0042] Figure 4The laser output linear polarization single pulse energy 1.68J laser spot and beam quality when the laser light is provided for an exemplary embodiment of the present application;

[0043] Figure 5 The pulse width when the laser output linear polarization single pulse energy 1.68J laser is provided for an exemplary embodiment of the present application, full width at half maximum 65ns;

[0044] Figure 6 The beam homogenization process schematic diagram provided for an exemplary embodiment of the present application simply demonstrates the change of the light spot before and after the beam homogenization from left to right;

[0045] Figure 7 The single pulse energy increase situation schematic diagram of the homogenized beam and the non-homogenized beam when the single pulse energy is incident under the same single pulse energy provided for an exemplary embodiment of the present application;

[0046] Among them,

[0047] 1, oscillator; 1-1, full mirror; 1-2, electro-optic Q KD * P crystal; 1-3, first 1064nm λ / 4 wave plate; 1-4, 1064nm polarization beam splitter prism; 1-5, 3mm Nd:YAG crystal rod oscillation side pump module; 1-6, output mirror;

[0048] 2, pre-amplifier; 2-1, pre-amplification beam transformation lens group; 2-2, first optical isolator and front 1064nm λ / 2 wave plate; 2-3, first 1064nm λ / 2 and λ / 4 wave plate; 2-4, 3mm Nd:YAG crystal rod pre-amplification side pump module; 2-5, first compensation lens;

[0049] 3, primary amplifier; 3-1, primary amplification beam transformation lens group; 3-2, second optical isolator and front 1064nm λ / 2 wave plate; 3-3, second 1064nm λ / 2 and λ / 4 wave plate; 3-4, 5mm Nd:YAG crystal rod primary side pump module I; 3-5, second compensation lens; 3-6, first quartz rotator; 3-7, 5mm Nd:YAG crystal rod primary side pump module II; 3-8, third compensation lens;

[0050] 4, secondary amplifier; 4-1, secondary amplification beam transformation lens group; 4-2, third optical isolator and front 1064nm λ / 2 wave plate; 4-3, third 1064nm λ / 2 and λ / 4 wave plate; 4-4, 8mm Nd:YAG crystal rod secondary side pump module I; 4-5, fourth compensation lens; 4-6, second quartz rotator; 4-7, 8mm Nd:YAG crystal rod secondary side pump module II; 4-8, fifth compensation lens;

[0051] 5, third stage main amplifier; 5-1, third stage main amplifier beam expander lens group; 5-2, fourth optical isolator and pre-1064nm λ / 2 wave plate; 5-3, fourth 1064nm λ / 2 and λ / 4 wave plate; 5-4, third stage side-pumped module I of 12mm Nd:YAG crystal rod; 5-5, sixth compensation lens; 5-6, third quartz rotator; 5-7, third stage side-pumped module II of 12mm Nd:YAG crystal rod; 5-8, seventh compensation lens; 5-9, second 1064nm λ / 4 wave plate;

[0052] 6, fourth stage main amplifier; 6-1, fifth optical isolator and pre-1064nm λ / 2 wave plate; 6-2, fifth 1064nm λ / 2 and λ / 4 wave plate; 6-3, fourth stage side-pumped module I of 12mm Nd:YAG crystal rod; 6-4, eighth compensation lens; 6-5, fourth quartz rotator; 6-6, fourth stage side-pumped module II of 12mm Nd:YAG crystal rod; 6-7, ninth compensation lens; 6-8, third 1064nm λ / 4 wave plate;

[0053] 7, polarization splitting switch;

[0054] 8, depolarization splitter;

[0055] 9, beam homogenizer; 9-1, 1064nm λ / 2 wave plate; 9-2, 1064nm beam homogenization sheet; 9-3, 1064nm polarization splitting prism. DETAILED DESCRIPTION

[0056] The application will be further described below in conjunction with the accompanying drawings and embodiments.

[0057] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0058] As described in the background, there is an urgent need for a high-repetition-frequency, high-beam-quality, joule-level and above single-pulse-energy laser with compact structure, stable performance, easy maintenance and good scalability. The present application provides a 1064nm all-solid-state laser based on beam homogenization and circularly polarized amplification, which can realize high-beam-quality, joule-level single-pulse-energy stable laser output at high repetition frequency, and has good anti-vibration performance and scalability.

[0059] As Figure 1As shown, the compact high-repetition high-beam-quality large-energy 1064nm all-solid-state laser based on the beam homogenization and circular polarization amplification technology of the application comprises an oscillator 1, a pre-amplifier 2, a first main amplifier 3, a second main amplifier 4, a third main amplifier 5 and a fourth main amplifier 6 arranged in sequence along the optical path.

[0060] The oscillator 1 of the application comprises a total reflection mirror 1-1, an electro-optic Q-switching KD * P crystal 1-2 (wherein KD * P crystal refers to potassium dideuterium phosphate crystal), a first 1064nm λ / 4 wave plate 1-3, a 1064nm polarization beam splitter prism 1-4, a 3mm Nd:YAG crystal rod oscillation side pump module 1-5 and an output mirror 1-6. The oscillator 1 outputs near-diffraction-limited fundamental mode seed light, and appropriate single-pulse energy output under appropriate pulse width can be obtained by using appropriate cavity length oscillation of the 3mm Nd:YAG crystal rod oscillation side pump module 1-5 and electro-optic Q-switching.

[0061] More specifically, the oscillator 1 of the application is a 3mm single-module electro-optic Q-switching Gaussian output mirror plano-convex cavity structure, which can output near-diffraction-limited fundamental mode seed light. Specifically, the average output power is 2.4W, the single-pulse energy is 8mJ, the beam quality M 2 In the horizontal direction and the vertical direction, the values are 1.03 and 1.02 respectively, and the out-of-cavity spot diameter is 1mm; the total reflection mirror 1-1 is a 1064nm high-reflection plane mirror; the output mirror 1-6 is a 1064nm gradually-changing-transmittance plano-convex Gaussian mirror, the Gaussian coating diameter is 2a=2.5, the minimum transmittance is 70%, the convex surface points to the inside of the cavity, and the curvature radius is 1.5m; the 1064nm polarization beam splitter prism 1-4 is used to realize single-polarized laser oscillation in the cavity, which can keep the oscillation path axis from geometrically deviating, and the pulse laser oscillation is realized by using the pressurized electro-optic Q-switching process, and the near-diffraction-limited fundamental mode laser output is realized by using appropriate cavity length, cavity type and Gaussian output mirror.

[0062] In the present embodiment, preferably, the atomic doping concentration of the 3mm Nd:YAG crystal rod in the oscillator 1 is 0.6%, the oscillation plano-convex cavity length is 850mm, and the oscillation seed light center wavelength is 1064.4nm, as shown in Figure 2 The spectral line width is 0.06nm, the oscillation seed light pulse width is 41ns, the oscillation seed light repetition frequency is 300Hz, and the oscillator depolarization light is 15mW.

[0063] The pre-amplifier 2 of the present application comprises a pre-amplification beam expander lens group 2-1, a first optical isolator and a front 1064nm λ / 2 wave plate 2-2, a first 1064nm λ / 2 and λ / 4 wave plate 2-3, a pre-amplification side pump module 2-4 of a 3mm Nd:YAG crystal rod and a first compensation lens 2-5, and the seed light is further amplified to have a single pulse energy.

[0064] In the present application, the pre-amplifier 2 is for further single pulse energy amplification of the seed light output by the oscillator 1, and the seed light with a single pulse energy of 8mJ is amplified by the pre-amplifier 2 after stripping and depolarizing the light, and the average output power is 5.8W when the pump current is 65A, the single pulse energy reaches 19mJ, and the beam quality M 2 The output spot diameter is 2mm in the horizontal direction and the vertical direction, respectively.

[0065] In the present embodiment, the seed light output by the oscillator 1 is expanded and collimated by the pre-amplification beam expander lens group 2-1, and then enters the pre-amplification side pump module 2-4 of the 3mm Nd:YAG crystal rod through the first optical isolator and the front 1064nm λ / 2 wave plate 2-2, and is amplified by the first 1064nm λ / 2 and λ / 4 wave plate 2-3, and the single pulse energy of the seed light is amplified on the basis of almost no deterioration of the spot shape and the beam quality, and the light output by the pre-amplification side pump module 2-4 of the 3mm Nd:YAG crystal rod is output through the first compensation lens 2-5.

[0066] More specifically, the pre-amplifier 2 of the present application has a front 1064nm λ / 2 and λ / 4 wave plate, which controls the polarization of the light beam to realize thermal-induced depolarization adjustment of the amplification process, so as to ensure the minimum depolarized light intensity; the pre-amplification side pump module 2-4 of the 3mm Nd:YAG crystal rod of the pre-amplifier 2 has the same specification parameters as the oscillation side pump module 1-5 of the 3mm Nd:YAG crystal rod of the oscillator 1, so as to ensure the minimum deterioration of the spot shape and the beam quality after pre-amplification; the first compensation lens 2-5 is introduced after pre-amplification, and the output light beam is well controlled through thermal lens compensation of a suitable concave mirror, which reduces the spherical aberration caused by the thermal lens, collimates the light beam with appropriate size, and improves the beam wavefront distortion at the far field.

[0067] In the present embodiment, preferably, the 3mm Nd:YAG crystal rod in the pre-amplifier 2 has an atomic doping concentration of 0.6%; the pre-amplification beam expander lens group is a spherical concave-convex lens group for expanding and collimating a Gaussian light beam by 2 times, and the oscillation seed light spot is expanded and collimated to 2mm after entering the optical isolator and the front 1064nm λ / 2 wave plate 2-2; the pulse width after pre-amplification is 45ns, and the pre-amplification depolarized light is 39mW.

[0068] The first-stage main amplifier 3, the second-stage main amplifier 4, the third-stage main amplifier 5 and the fourth-stage main amplifier 6 are used for completing step-by-step amplification of laser pulses.

[0069] The first-stage main amplifier 3 comprises a first-stage main amplification variable-beam lens group 3-1, a second optical isolator and a front 1064nm λ / 2 wave plate 3-2, a second 1064nm λ / 2 and λ / 4 wave plate 3-3, a first-stage side-pumped module I of a 5mm Nd:YAG crystal rod 3-4, a second compensation lens 3-5, a first quartz rotator 3-6, a first-stage side-pumped module II of a 5mm Nd:YAG crystal rod 3-7 and a third compensation lens 3-8 arranged in sequence along an optical path.

[0070] The second-stage main amplifier 4 comprises a second-stage main amplification variable-beam lens group 4-1, a third optical isolator and a front 1064nm λ / 2 wave plate 4-2, a third 1064nm λ / 2 and λ / 4 wave plate 4-3, a second-stage side-pumped module I of an 8mm Nd:YAG crystal rod 4-4, a fourth compensation lens 4-5, a second quartz rotator 4-6, a second-stage side-pumped module II of an 8mm Nd:YAG crystal rod 4-7 and a fifth compensation lens 4-8 arranged in sequence along an optical path.

[0071] The third-stage main amplifier 5 comprises a third-stage main amplification variable-beam lens group 5-1, a fourth optical isolator and a front 1064nm λ / 2 wave plate 5-2, a fourth 1064nm λ / 2 and λ / 4 wave plate 5-3, a third-stage side-pumped module I of a 12mm Nd:YAG crystal rod 5-4, a sixth compensation lens 5-5, a third quartz rotator 5-6, a third-stage side-pumped module II of a 12mm Nd:YAG crystal rod 5-7, a seventh compensation lens 5-8 and a second 1064nm λ / 4 wave plate 5-9 arranged in sequence along an optical path.

[0072] The fourth-stage main amplifier 6 comprises a fifth optical isolator and a front 1064nm λ / 2 wave plate 6-1, a fifth 1064nm λ / 2 and λ / 4 wave plate 6-2, a fourth-stage side-pumped module I of a 12mm Nd:YAG crystal rod 6-3, an eighth compensation lens 6-4, a fourth quartz rotator 6-5, a fourth-stage side-pumped module II of a 12mm Nd:YAG crystal rod 6-6, a ninth compensation lens 6-7 and a third 1064nm λ / 4 wave plate 6-8 arranged in sequence along an optical path.

[0073] In the present implementation, the first quartz rotator 3-6, the second quartz rotator 4-6, the third quartz rotator 5-6 and the fourth quartz rotator 6-5 have the same function, i.e., rotating the polarization of laser by 90 degrees by using the birefringence effect of quartz crystal.

[0074] In the present implementation, the laser beam output by the secondary main amplifier 4 is controlled and optimized by the beam homogenizer 9, including a 1064nm λ / 2 wave plate 9-1, a 1064nm beam homogenization sheet 9-2 and a 1064nm polarization beam splitter prism 9-3 arranged in sequence along the optical path, the effective diameter of the 1064nm beam homogenization sheet 9-2 is 8mm, and the homogenized spot diameter is 5.5mm.

[0075] In the present application, the laser beam output by the preamplifier 2 is expanded and collimated by the first main amplification beam expander lens group 3-1 after amplification, then passes through the second optical isolator and the front 1064nm λ / 2 wave plate 3-2, and is controlled by the second 1064nm λ / 2 and λ / 4 wave plate 3-3, and then enters the first side-pumped module I 3-4 of the 5mm Nd:YAG crystal rod for amplification, and then passes through the second compensation lens 3-5, and then passes through the first quartz rotator 3-6 for polarization vertical rotation, and then enters the first side-pumped module II 3-7 of the 5mm Nd:YAG crystal rod for amplification, and then passes through the third compensation lens 3-8 for output;

[0076] The laser beam output by the first main amplifier 3 passes through the polarization beam splitter switch 7, and then passes through the second main amplification beam expander lens group 4-1 for expansion and collimation, and then passes through the third optical isolator and the front 1064nm λ / 2 wave plate 4-2, and is controlled by the third 1064nm λ / 2 and λ / 4 wave plate 4-3, and then enters the second side-pumped module I 4-4 of the 8mm Nd:YAG crystal rod for amplification, and then passes through the fourth compensation lens 4-5, and then passes through the second quartz rotator 4-6 for polarization vertical rotation, and then enters the second side-pumped module II 4-7 of the 8mm Nd:YAG crystal rod for amplification, and then passes through the fifth compensation lens 4-8 for output;

[0077] The polarization beam splitter switch 7 is composed of a 1064nm λ / 2 wave plate and a polarization beam splitter prism, which can control the laser intensity entering the secondary main amplifier 4 from complete shutdown to maximum light output without step adjustment, and can realize intensity control from zero light output to maximum light output under the condition that the secondary main amplifier 4, the tertiary main amplifier 5 and the quaternary main amplifier 6 are all powered at full power.

[0078] The laser beam output by the secondary main amplifier 4 passes through the depolarization light separator 8 to strip off the depolarization light, and then enters the beam homogenizer 9, which is controlled by the 1064nm λ / 2 wave plate 9-1, and then passes through the 1064nm beam homogenization sheet 9-2 for phase polarization conversion, and then passes through the 1064nm polarization beam splitter prism 9-3 for light splitting, to complete the beam control and optimization; by using the beam homogenization process, the intensity of the spot core can be appropriately filtered out, and the dark and weak distorted part of the outermost periphery of the spot can be removed, so that a nearly ideal beam is obtained. Although the beam homogenization process reduces the laser power, the nearly ideal beam can obtain better amplification extraction efficiency after expansion and collimation.

[0079] The homogenized laser beam is expanded and collimated by the three-stage main amplification beam expander lens group 5-1, and then passes through the fourth optical isolator and the front 1064 nm λ / 2 wave plate 5-2, and then is polarized by the fourth 1064 nm λ / 2 and λ / 4 wave plate 5-3, and then is amplified by the three-stage side-pumped module I 5-4 of the 12 mm Nd:YAG crystal rod, and then passes through the sixth compensation lens 5-5, and then is polarized vertically by the third quartz rotator 5-6, and then is amplified by the three-stage side-pumped module II 5-7 of the 12 mm Nd:YAG crystal rod, and then passes through the seventh compensation lens 5-8 and the second 1064 nm λ / 4 wave plate 5-9 to output;

[0080] The laser beam output by the three-stage main amplifier 5 passes through the fifth optical isolator and the front 1064 nm λ / 2 wave plate 6-1, and then is polarized by the fifth 1064 nm λ / 2 and λ / 4 wave plate 6-2, and then is amplified by the four-stage side-pumped module I 6-3 of the 12 mm Nd:YAG crystal rod, and then passes through the eighth compensation lens 6-4, and then is polarized vertically by the fourth quartz rotator 6-5, and then is amplified by the four-stage side-pumped module II 6-6 of the 12 mm Nd:YAG crystal rod, and then passes through the ninth compensation lens 6-7 and the third 1064 nm λ / 4 wave plate 6-8 to output.

[0081] More specifically, taking the 18 mJ single pulse energy laser after pre-amplification depolarization as an example, the subsequent four-stage amplification and homogenization process is as follows:

[0082] After amplification by the first-stage main amplifier 3, the average output power is 35.6 W when the pump current is 65 A, the single pulse energy reaches 119 mJ, and the output spot diameter is 4 mm; the 5 mm Nd:YAG crystal rod of the first-stage main amplifier 3 has an atomic doping concentration of 0.6%, and the first-stage main amplification beam expander lens group 3-1 is a spherical concave-convex lens group that expands and collimates the pre-amplified light spot by 2 times in a Gaussian beam, and after expanding and collimating the pre-amplified light spot to 4 mm, the light enters the second optical isolator and the front 1064 nm λ / 2 wave plate 3-2 of the first-stage main amplifier 3; the pulse width after processing by the first-stage main amplifier 3 is 50 ns, and the depolarization light is 0.5 W.

[0083] The 109mJ single pulse energy laser after the first main amplifier 3 stripping the depolarization light, after the polarization light splitting switch 7, and then amplified by the second main amplifier 4, the average output power is 129W when the pumping current is 85A, the single pulse energy reaches 430mJ, and the output spot diameter is 6mm. The atomic doping concentration of the 8mm Nd:YAG crystal rod of the second main amplifier is 0.6%, and the second main amplifier beam expander lens group 4-1 is a spherical concave-convex lens group for expanding and collimating the Gaussian beam by 1.5 times, which expands and collimates the first main amplifier spot to 6mm into the third optical isolator and the front 1064nm λ / 2 wave plate 4-2 of the second main amplifier 4. The pulse width after the second main amplifier processing is 55ns, and the depolarization light is 6W.

[0084] The laser beam output by the second main amplifier 4 is stripped of the depolarization light by the depolarization separator 8, and then passes through the beam homogenizer 9, and the single pulse energy is reduced to 283mJ, the average power is 85W, and the laser spot diameter after beam homogenization is 5.5mm. The power of the strong core and the weak ring part removed in the beam homogenization process is 37.7W.

[0085] The depolarization separator 8 is composed of a 1064nm λ / 2 wave plate and a polarization light splitting prism, which mainly filters out the depolarization light generated in the second main amplification process to avoid interference and influence on the subsequent beam homogenization process.

[0086] The 283mJ single pulse energy laser after homogenization is amplified by the third main amplifier 5, the average output power is 264W when the pumping current is 80A, the single pulse energy reaches 880mJ, and the output spot diameter is 10mm. The atomic doping concentration of the 12mm Nd:YAG crystal rod of the third main amplifier 5 is 0.6%; the third main amplifier beam expander lens group 5-1 is a spherical concave-convex lens group for expanding and collimating the Gaussian beam by 1.75 times, which expands and collimates the beam homogenization spot to 10mm into the fourth optical isolator and the front 1064nm λ / 2 wave plate 5-2. The pulse width after the third main amplifier processing is 60ns, and the depolarization light is 11W.

[0087] In the present embodiment, preferably, the third main amplifier 5 adopts a circular polarization amplification process, that is, when the third double module amplification is performed, the beam horizontal polarization state is first converted into a circular polarization state, and then enters the third side pump module I 5-4 of the 12mm Nd:YAG crystal rod for amplification. After the third side pump module II 5-7 of the 12mm Nd:YAG crystal rod, the beam is converted back to the horizontal polarization state. Compared with the horizontal polarization state, the circular polarization state can effectively weaken the self-focusing intensity under the large energy pulse and optimize the amplification process because of the rotation of the electric vector, and combined with the beam homogenization process, the beam quality and spot deterioration caused by thermal distortion can be well controlled.

[0088] The 843mJ single pulse energy laser after depolarization is amplified by the fourth main amplifier 6, the output average power is 525W under the pump current of 80A, the single pulse energy reaches 1.75J, and the average power of linearly polarized laser output is 505W after 20W depolarization, as shown in Figure 3 Fig. 1, the single pulse energy is 1.68J, and the beam quality M 2 The output spot diameter is 10mm in the horizontal and vertical directions, and the far field divergence angle is 0.24mrad, as shown in Figure 4 Fig. 1, the pulse width of the 12mm Nd:YAG crystal rod of the fourth main amplifier is 65ns, as shown in Figure 5 Fig. 1, and the depolarization is 20W.

[0089] In the present embodiment, the fourth main amplifier 6 adopts a circular polarization amplification process, that is, when the fourth double module amplification is performed, the beam is first converted from a horizontal polarization state to a circular polarization state, then enters the fourth side pump module I 6-3 of the 12mm Nd:YAG crystal rod for amplification, and then the beam is converted back to a horizontal polarization state after passing through the fourth side pump module II 6-6 of the 12mm Nd:YAG crystal rod. Compared with the horizontal polarization state, the circular polarization state has a rotation of the electric vector, which can effectively weaken the self-focusing intensity under the large energy pulse and optimize the amplification process, and in combination with the beam homogenization process, the beam quality and spot deterioration caused by thermal distortion can be well controlled.

[0090] As shown in Figure 6 Fig. 1, it is a schematic diagram of the beam homogenization process, which simply demonstrates the change of the spot before and after the beam homogenization; as shown in Figure 7 Fig. 1, under the same single pulse energy, the single pulse energy increases when the homogenized beam and the non-homogenized beam pass through the third main amplifier, the single pulse energy is 283mJ after homogenization, and the average power is 85W, after the third main amplifier double module amplification (black represents the single pulse energy of the third side pump module I of the 12mm Nd:YAG crystal rod after homogenization, red represents the single pulse energy of the third side pump module II of the 12mm Nd:YAG crystal rod after homogenization, blue represents the single pulse energy of the third side pump module I of the 12mm Nd:YAG crystal rod without homogenization, and green represents the single pulse energy of the third side pump module II of the 12mm Nd:YAG crystal rod without homogenization), the single pulse energy increases to 880mJ under the pump current of 80A, and the average power is 264W, while the same single pulse energy and average power laser beam without homogenization increases to 793mJ after the third main amplifier double module amplification, and the average power is 238W under the pump current of 80A.

[0091] In comparison, the homogenized laser beam has a 10.9% increase in single pulse energy after the next stage of amplification at the same single pulse energy. In order to more intuitively illustrate, the present application uses two modules of the three-stage main amplification to reflect the amplification growth process of the homogenized beam and the non-homogenized beam, respectively. After the homogenized beam is sequentially amplified by the two modules of the three-stage main amplification, the fitting slope of the single pulse energy growth to the increase of the pump current is 3.87 mJ / A for LD I and 5.83 mJ / A for LD II, which can be regarded as the average growth rate of the amplification process. After the non-homogenized beam with the same single pulse energy is sequentially amplified by the two modules of the three-stage main amplification, the fitting slope of the single pulse energy growth to the increase of the pump current is 3.27 mJ / A for LD I and 5.03 mJ / A for LD II. Under the same single pulse energy, the average growth rate of the homogenized beam in the amplification process is increased by 18.3% (LD I) and 15.9% (LD II) compared with the non-homogenized beam, which fully illustrates the control and optimization of the homogenization process on the beam. At the same time, the reduction of the core intensity of the beam and the elimination of the dark and weak distortion part at the outermost periphery are more conducive to reducing the deterioration of the spot shape after the three-stage main amplification, thereby ensuring the extraction efficiency of the four-stage main amplification and the spot shape and beam quality after amplification.

[0092] In the present embodiment, preferably, a compensation lens is introduced after each amplification module (i.e., each side-pumping module), and the output beam is well controlled through appropriate thermal lens compensation of the concave mirror, which reduces the spherical aberration caused by the thermal lens, collimates the beam with appropriate size, and improves the beam wavefront distortion at the far field.

[0093] In the present embodiment, preferably, the four-stage main amplifiers are designed as double modules with the same specification parameters, and a quartz rotator is introduced between the two modules to vertically rotate the polarization, so that the same amplification process with vertically polarized polarization can well compensate the thermal depolarization caused by the amplification process to reduce the depolarized light intensity.

[0094] In the present embodiment, preferably, the four-stage main amplifiers use the same 12mm crystal module as the three-stage main amplifiers. Firstly, from the theoretical analysis, the 12mm crystal module can completely realize the output power of Joule level and above. Secondly, from the technical analysis, if a larger size crystal module is used, the beam needs to be further expanded and collimated, and the larger the size of the beam, the faster the beam quality deteriorates during the amplification process. Thirdly, using a lower energy consumption and smaller device makes the output more reliable and stable. Fourthly, using the 12mm crystal module is easy to expand to five-stage main amplification.

[0095] The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1.A 1064nm all-solid-state laser based on beam homogenization and circular polarization amplification, characterized in that, it comprises, in sequence along an optical path, an oscillator for providing a fundamental mode seed light, a pre-amplifier for amplifying the single pulse energy of the seed light output by the oscillator, a first main amplifier, a second main amplifier, a third main amplifier and a fourth main amplifier, the first main amplifier, the second main amplifier, the third main amplifier and the fourth main amplifier sequentially amplify the seed light amplified by the pre-amplifier and output 1064nm laser light, and a beam homogenizer is arranged on the optical path between the second main amplifier and the third main amplifier; in the third main amplifier and the fourth main amplifier, the horizontal polarization state of the light beam is first converted into a circular polarization state, and the circularly polarized light is amplified and then converted back into a horizontal polarization state. 2.The 1064nm all-solid-state laser based on beam homogenization and circular polarization amplification according to claim 1, characterized in that, 3.The 1064nm all-solid-state laser based on beam homogenization and circular polarization amplification according to claim 1, characterized in that, the pre-amplifier comprises, in sequence along an optical path, a pre-amplification beam-shaping lens group, a first optical isolator, a front 1064nm λ / 2 wave plate, a first 1064nm λ / 2 and λ / 4 wave plate, a pre-amplification side pump module of a 3mm Nd:YAG crystal rod, and a first compensation lens. 4.The 1064nm all-solid-state laser based on beam homogenization and circular polarization amplification according to claim 1, characterized in that, The oscillator comprises a total reflection mirror, an electro-optic Q-switching KD * P crystal, a first 1064 nm λ / 4 wave plate, a 1064 nm polarization beam splitter prism, a 3 mm Nd:YAG crystal rod oscillation side pump module, and an output mirror. the first main amplifier comprises, in sequence along an optical path, a first main amplification beam-shaping lens group, a second optical isolator, a front 1064nm λ / 2 wave plate, a second 1064nm λ / 2 and λ / 4 wave plate, a first side pump module I of a 5mm Nd:YAG crystal rod, a second compensation lens, a first quartz rotator, a second side pump module II of a 5mm Nd:YAG crystal rod, and a third compensation lens; the second main amplifier comprises, in sequence along an optical path, a second main amplification beam-shaping lens group, a third optical isolator, a front 1064nm λ / 2 wave plate, a third 1064nm λ / 2 and λ / 4 wave plate, a second side pump module I of an 8mm Nd:YAG crystal rod, a fourth compensation lens, a second quartz rotator, a second side pump module II of an 8mm Nd:YAG crystal rod, and a fifth compensation lens; the third main amplifier comprises, in sequence along an optical path, a third main amplification beam-shaping lens group, a fourth optical isolator, a front 1064nm λ / 2 wave plate, a fourth 1064nm λ / 2 and λ / 4 wave plate, a third side pump module I of a 12mm Nd:YAG crystal rod, a sixth compensation lens, a third quartz rotator, a third side pump module II of a 12mm Nd:YAG crystal rod, a seventh compensation lens, and a second 1064nm λ / 4 wave plate. ​ ​ ​ The fourth-stage main amplifier comprises, in sequence along the light path, a fifth optical isolator, a front 1064nm λ / 2 wave plate, a fifth 1064nm λ / 2 and λ / 4 wave plate, a four-stage side-pumped module I of a 12mm Nd:YAG crystal rod, an eighth compensation lens, a fourth quartz rotator, a four-stage side-pumped module II of a 12mm Nd:YAG crystal rod, a ninth compensation lens, and a third 1064nm λ / 4 wave plate. 5.The 1064nm all-solid-state laser based on beam homogenization and circular polarization amplification according to claim 4, wherein, The first-stage main amplification variable-beam lens group is a spherical concave-convex lens group for expanding and collimating a Gaussian light beam by 2 times. The second-stage main amplification variable-beam lens group is a spherical concave-convex lens group for expanding and collimating a Gaussian light beam by 1.5 times. The third-stage main amplification variable-beam lens group is a spherical concave-convex lens group for expanding and collimating a Gaussian light beam by 1.75 times. 6.The 1064nm all-solid-state laser based on beam homogenization and circular polarization amplification according to claim 4, wherein, The first, second, third, and fourth quartz rotators all rotate the polarization of laser light by 90 degrees by using the birefringence effect of a quartz crystal. 7.The 1064nm all-solid-state laser based on beam homogenization and circular polarization amplification according to claim 1, wherein, A polarization beam splitter is arranged on the light path between the first-stage main amplifier and the second-stage main amplifier. 8.The 1064nm all-solid-state laser based on beam homogenization and circular polarization amplification according to claim 1, wherein, The laser output by the second-stage main amplifier is first processed by a depolarization light separator and then subjected to beam homogenization processing. 9.The 1064nm all-solid-state laser based on beam homogenization and circular polarization amplification according to claim 1, wherein, The beam homogenizer comprises, in sequence along the light path, a 1064nm λ / 2 wave plate, a 1064nm beam homogenization sheet, and a 1064nm polarization beam splitter prism. 10.A 1064nm laser generation method using the 1064nm all-solid-state laser based on beam homogenization and circular polarization amplification according to any one of claims 1-9, comprising the following processes: Start the oscillator, and output a fundamental mode seed light from the oscillator; Input the fundamental mode seed light output by the oscillator into the pre-amplifier, and perform single-pulse energy amplification on the fundamental mode seed light by the pre-amplifier; Input the seed light amplified by the pre-amplifier into the first-stage main amplifier and the second-stage main amplifier in sequence, and perform step-by-step energy amplification by the first-stage main amplifier and the second-stage main amplifier in sequence; Introduce the laser amplified by the second-stage main amplifier into the beam homogenizer, and perform homogenization processing on the laser beam by the beam homogenizer; Input the homogenization-processed laser into the third-stage main amplifier, first convert the horizontal polarization state of the light beam into a circular polarization state by the λ / 4 wave plate in front of the third-stage main amplifier, perform energy amplification on the laser in the circular polarization state, and then convert it back into a horizontal polarization state by the λ / 4 wave plate. The laser processed by the three-stage main amplifier is input into a four-stage main amplifier, the horizontal polarization state of the light beam is first converted into a circular polarization state by a λ / 4 wave plate in front of the four-stage main amplifier, the circular polarization state laser is amplified in energy, and then the λ / 4 wave plate is used to convert it back to the horizontal polarization state, and finally the 1064nm laser is output.

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