Laser side pump four-way amplifier and amplification method and device thereof

Abstract

The invention provides a laser side pump four-way amplifier and an amplification method and device thereof. The four-way amplifier comprises a laser module, an isolation module, a side pump module, an image transmission module, a nonlinear crystal module and a reflection module. Based on the image transmission structure and the spatial light modulator, wavefront phase distortion is compensated while the pass number is increased, and the high-beam-quality and high-efficiency amplification effect is achieved. By adjusting the polarization of the seed light and combining the polarization device, the seed light passes through the amplification crystal for four times, the efficiency of extracting gain by the seed light is greatly improved, and high-power output is realized in a light path with a simple structure.

Description

Technical Field

[0001] The invention belongs to the technical field of ultrafast and ultra-strong lasers, and in particular relates to a laser side-pump four-way amplifier, and an amplification method and device thereof. Background Art

[0002] Picosecond pulse lasers have been widely used in many fields due to their high peak power and simple structure. In particular, picosecond lasers with pulse energies above ten millijoules and average powers of tens of watts, which are both high energy and high power, have important applications in industrial processing, scientific research, military defense, etc. However, the energy of picosecond pulses generated by direct mode locking is mostly in the nanojoule level, which is difficult to meet the needs of industrial processing and other applications, and the pulses need to be amplified.

[0003] In high-energy picosecond laser amplification, the side pumping method of neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal can achieve extremely high pumping power and large-area water cooling on the side, and has become the main gain medium pumping solution. In addition, Nd:YAG has a high gain and can achieve high energy output through traveling wave amplification, up to hundreds of millijoules.

[0004] Generally, side-pumped traveling wave amplifiers mainly adopt single-pass or dual-pass amplification, and a few adopt four-pass amplification to increase the gain multiple. In the past, they mainly operated at 100Hz or even lower repetition frequency, and their average power was not high. When the system operates at 1kHz or even higher repetition frequency, the average power of the pump increases significantly, even reaching the kilowatt level, causing the temperature distribution in the middle of the crystal to present a radial gradient. The thermal effect is very serious, causing the incident laser to produce obvious thermally induced wavefront phase distortion, thereby affecting the output beam quality and limiting energy amplification.

[0005] In summary, the prior art has the following disadvantages:

[0006] 1. Under high repetition rate operation, thermally induced wavefront phase distortion affects the output beam quality.

[0007] 2. During picosecond laser amplification, high pulse energy is prone to nonlinear self-focusing, affecting the beam quality. Summary of the invention

[0008] Therefore, the object of the present invention is to overcome the defects in the prior art and provide a laser side-pumped four-way amplifier, and an amplification method and device thereof.

[0009] Before describing the present invention, the terms used in this article are defined as follows:

[0010] The term "HT" means: High Transmission.

[0011] The term "Nd:YAG" means: Neodymium-doped Yttrium Aluminum Garnet.

[0012] The term "SLM" refers to: Spatial light modulator, which is a diffractive optical device that modulates the wavefront of light waves. It can modulate light beams to generate a pre-designed spatial light field. It can control the input of a time-varying driving signal to achieve modulation of the polarization state, amplitude, phase and other physical quantities of the incident light field.

[0013] The term "seed light" refers to unamplified laser light.

[0014] The term "Nd:YLF" means: Neodymium-doped Yttrium Lithium Fluoride crystal.

[0015] To achieve the above object, a first aspect of the present invention provides a laser side-pumped four-way amplifier, the laser side-pumped four-way amplifier comprising:

[0016] A laser module for outputting laser light;

[0017] Side pump module for laser amplification;

[0018] Isolation module for changing laser polarization and blocking return light caused by thermal depolarization effect of side pump module;

[0019] An image transfer module for completely transferring the light spot;

[0020] Nonlinear crystal modules for compensating for beam self-focusing effects; and

[0021] A reflection module for reflecting the laser light amplified by the side pump module and then passing it through the side pump module again for a second amplification;

[0022] in:

[0023] The image transmission module includes a first image transmission module and a second image transmission module;

[0024] The nonlinear crystal module includes a first nonlinear crystal module and a second nonlinear crystal module;

[0025] The reflection module includes a first reflection module and a second reflection module.

[0026] According to the laser side pump four-pass amplifier of the first aspect of the present invention, wherein:

[0027] The output end of the laser module is connected to the input end of the isolation module;

[0028] One of the output ends of the isolation module is connected to the input end of the side pump module, the output end of the side pump module is connected to the input end of the first image transfer module, the output end of the first image transfer module is connected to the input end of the first nonlinear crystal module, and the output end of the first nonlinear crystal module is connected to the output input end of the first reflection mode; and / or

[0029] Another path of the output end of the isolation module is connected to the input end of the second image transmission module through a transmission beam reflector and / or a transmission beam thin film polarizer, the output end of the second image transmission module is connected to the input end of the second nonlinear crystal module, and the output end of the second nonlinear crystal module is connected to the output input end of the second reflection module;

[0030] Preferably, the reflection angle of the transmission light beam reflector is 30-45°, more preferably 34.4-45°.

[0032] According to the laser side-pumped four-way amplifier of the first aspect of the present invention, the isolation module comprises an optical isolator and a thin-film polarizer; wherein,

[0033] The optical isolator comprises in sequence: a thin film polarizer of the optical isolator, a Faraday rotator and a half-wave plate of the optical isolator;

[0034] The thin film polarizer is coated on both sides, one side is coated with a polarizing film with an incident angle of 55.6°, and the other side is coated with an anti-reflection film;

[0035] The number of the thin film polarizers is 3 to 5, preferably 3 to 4, most preferably 3; and / or

[0036] The picosecond laser emits P-polarized laser light, and after passing through the optical isolator, the P-polarized laser light is converted into S-polarized laser light;

[0037] Preferably, at a wavelength of 1064 nm, the polarizing film satisfies an extinction ratio greater than 1000:1, and the antireflection film has a HT>99%; and / or

[0038] Preferably, at least one thin-film polarizer is arranged after the optical isolator.

[0039] According to the laser side-pumped four-way amplifier of the first aspect of the present invention, the side-pump module comprises a side-pump module crystal; wherein,

[0040] The side pump module crystal is a Nd:YAG side pump module crystal or a Nd:YLF side pump module crystal, and the most preferred one is a Nd:YAG side pump module crystal;

[0041] The shape of the side pump module crystal is a round rod or a long strip, and the most preferred shape is a round rod;

[0042] The side and both ends of the side pump module crystal are coated with a film; wherein the wavelength of the film on the side is 808-888nm, preferably 818-868nm, and most preferably 808nm; the wavelength of the film on both ends is 1000-1100nm, preferably 1020-1080nm, and most preferably 1064nm; and / or

[0043] The pumping mode of the side pump module is end pumping and / or side pumping, and the most preferred mode is side pumping;

[0044] Preferably, a quarter wave plate for converting linearly polarized laser light into circularly polarized laser light is further included before the side pump module crystal; and / or

[0045] Preferably, the light transmittance of the film is greater than 90%, more preferably greater than 95%, and further preferably greater than 99.99%.

[0046] According to the laser side-pumped four-way amplifier of the first aspect of the present invention, the first image transfer module and the second image transfer module both include: a convex lens and a vacuum tube;

[0047] A small hole with biaxial adjustment is installed at the focus of the vacuum tube;

[0048] The convex lens is a plano-convex lens or a bi-convex lens, and is most preferably a plano-convex lens;

[0049] The number of the convex lenses is 1 to 4, preferably 2 to 3, and most preferably 2; and / or

[0050] The convex lenses have the same focal length and are confocal;

[0051] Preferably, when the number of the convex lenses is 2,

[0052] The first image transmission module and the second image transmission module further include: a first convex lens, a vacuum tube and a second convex lens, wherein the vacuum tube is located between the first convex lens and the second convex lens; and / or

[0053] The second convex lens is mounted on the translation stage.

[0054] According to the laser side pump four-pass amplifier of the first aspect of the present invention, wherein:

[0055] The first nonlinear crystal module comprises: a Faraday rotator and a nonlinear crystal; and / or

[0056] The second nonlinear crystal module includes a nonlinear crystal;

[0057] Preferably, the nonlinear crystal has a negative nonlinear refractive index.

[0058] According to the laser side-pumped four-way amplifier of the first aspect of the present invention, the first reflection module and the second reflection module both include: a spatial reflection mirror and / or a spatial light modulator;

[0059] Preferably, the spatial light modulator is selected from one or more of the following: liquid crystal spatial light modulator, electro-optical spatial light modulator, magneto-optical spatial light modulator, acousto-optical spatial light modulator, thermo-optical spatial light modulator, more preferably selected from one or more of the following: liquid crystal spatial light modulator, electro-optical spatial light modulator, magneto-optical spatial light modulator, most preferably a liquid crystal spatial light modulator;

[0060] Preferably, the reflection angle of the space reflector is 0-5°, most preferably 0°; and / or

[0061] Preferably, the space reflectors are all coated, and the reflectivity of the coating is more preferably greater than 95%, further preferably greater than 98%, and even more preferably greater than 99%.

[0062] According to the laser side-pumped four-way amplifier of the first aspect of the present invention, the laser module comprises a laser, and the laser is preferably a picosecond laser;

[0063] The pulse width of the picosecond laser is preferably 10 to 800 ps, ​​more preferably 20 to 500 ps, ​​further preferably 30 to 100 ps, ​​and most preferably 60 ps.

[0064] A second aspect of the present invention provides a laser amplification method, the laser amplification method comprising using the laser side-pumped four-pass amplifier described in the first aspect;

[0065] Preferably, the amplification method includes: the laser module emits P-polarized laser light, which is converted into S-polarized laser light through the thin-film polarizer and the optical isolator in sequence, and then is transmitted through the thin-film polarizer located behind the optical isolator and converted into circularly polarized laser light through the quarter-wave plate, and then enters the side pump module for the first amplification; the amplified light beam passes through the first image transfer module and the first nonlinear crystal module in sequence, is reflected by the first reflection module, and then passes through the first nonlinear crystal module and the first image transfer module again to enter the side pump module for the second amplification; since the seed light passes through the quarter-wave plate twice, the P polarization is converted into S polarization; then, the light beam passes through the thin-film polarizer located behind the optical isolator, the transmission beam thin-film polarizer and / or the transmission beam reflector used to connect the isolation module and the second image transfer module, the second image transfer module, and the second nonlinear crystal module in sequence, and then is reflected by the second reflection module and then returns to the side pump module along the original path for the third amplification; then, the light beam passes through the first image transfer module and the first nonlinear crystal module in sequence, is reflected by the first reflection module, and then returns to the side pump module along the original path for the fourth amplification; the laser light is converted from S polarization to P polarization again, and finally is transmitted out from the thin-film polarizer located behind the optical isolator.

[0066] A third aspect of the present invention provides a pulse laser device, the pulse laser device comprising the laser side-pumped four-way amplifier according to the first aspect;

[0067] Preferably, the pulse laser device is a picosecond pulse laser device.

[0068] To achieve the above-mentioned purpose, according to a preferred embodiment of the present invention, the four-way amplifier includes: a picosecond laser 1, a third thin-film polarizer 5, a quarter-wave plate 6, an Nd:YAG side pump module 7, a first 0° spatial reflector or spatial light modulator 11, a transfer beam reflector 12, and a second 0° spatial reflector or spatial light modulator 15, and the reflection angle of the transfer beam reflector 12 is 34.4°.

[0069] Preferably, the thin film polarizer is double-sided coated, requiring the polarizing film to be coated on the front surface of the thin film polarizer, with an incident angle of 55.6°, and more preferably, satisfying an extinction ratio greater than 1000:1 at a wavelength of 1064nm; and the anti-reflection film to be coated on the back surface of the thin film polarizer, and more preferably, HT>99% at a wavelength of 1064nm. The light beam is split on the front surface of the thin film polarizer, and the transmitted light passes through the high-transmittance film on the back surface to avoid reflection.

[0070] Preferably, the reflectors are coated with a 1064nm high-reflection film, and the reflectivity of the high-reflection film to the wavelength of incident light is more preferably 95%, and further preferably 99%.

[0071] Preferably, the Nd:YAG side pump module crystal is in the shape of a round rod, which is conducive to heat dissipation and is doped with Nd3+ The doping concentration is 0.6at%, and the side is coated with 808nm high-transmittance film, and the two ends are coated with 1064 high-transmittance film. The pump light wavelength is 808nm, and the pumping method is side pumping.

[0072] Preferably, a liquid crystal SLM spatial light modulator is used to compensate for the wavefront phase distortion in light beam transmission to obtain a high beam quality and high efficiency amplification effect.

[0073] The picosecond laser 1 emits a P-polarized seed light, which is transmitted through the third thin-film polarizer 5 and the quarter-wave plate 6 and then enters the Nd:YAG side pump module for amplification. The amplified light beam is reflected by the first 0° spatial reflector or spatial light modulator 11 and then enters the side pump module again for a second amplification. Since the seed light passes through the quarter-wave plate twice, the P polarization is converted to S polarization, so it will be reflected by the third thin-film polarizer 5, the transfer beam reflector 12 and the second 0° spatial reflector or spatial light modulator 15, and then return to the side pump module for the third amplification, and then be reflected by the first 0° spatial reflector or spatial light modulator 11 and enter the side pump module for the fourth amplification. The seed light is again converted from S polarization to P polarization and finally transmitted out from the thin-film polarizer 5.

[0074] Furthermore, it also includes an optical isolator 4, a first thin-film polarizer 2, and a second thin-film polarizer 3: the seed light emitted by the picosecond laser is reflected by the two thin-film polarizers and enters the optical isolator 4, the S polarization is converted into P polarization, enters the third thin-film polarizer and then enters the side pump module.

[0075] Furthermore, it also includes a first image transmission module 8 and a second image transmission module 13 .

[0076] Preferably, the image transfer module is composed of two plano-convex lenses with the same focal length and common focal point, and the second lens is mounted on a translation stage to facilitate the control of the spot size of the image transfer. More preferably, a vacuum tube is installed between the two lenses to prevent the laser from ionizing at the focus. It is further preferred to install a small hole with two-axis adjustment at the focus of the vacuum tube to filter and block the light spot reflected by the lens. The role of image transfer is to completely transfer the light spot at the position with good beam quality to the position required next time, thereby avoiding the deterioration of the beam in natural transmission.

[0077] Preferably, a quarter wave plate is added before the side pump module to convert linearly polarized light into circularly polarized light to reduce nonlinear effects.

[0078] Preferably, the optical isolator is composed of a thin film polarizer, a Faraday rotator and a half-wave plate, which are used to change the polarization of the laser and block the laser with impure polarization caused by thermal depolarization effect to avoid damage to the components.

[0079] The invention provides a four-pass amplifier based on a side pump module, which comprises a thin film polarizer, an optical rotator, a half-wave plate, a thin film polarizer, a quarter-wave plate, a side pump amplification module, a first image transfer, an optical rotator, a 0-degree reflector, a second spatial filter image transfer, a negative nonlinear refractive index material, a 0-degree reflector or a spatial light modulator. Based on the image transfer structure and the spatial light modulator, the invention increases the number of passes while compensating for wavefront phase distortion, thereby obtaining an amplification effect with high beam quality and high efficiency.

[0080] By adjusting the polarization of the seed light and combining it with a polarization device to allow it to pass through the amplifying crystal four times, the efficiency of seed light extraction gain is greatly improved, and high-power output is achieved in a simple optical path.

[0081] The invention relates to the field of ultrafast and ultra-strong lasers, and is suitable for energy and power amplification of ultrashort lasers, so as to more efficiently and effectively improve the output energy and power of lasers.

[0082] The prior art generally does not use phase compensation and nonlinear compensation devices. Under high repetition rate and high energy, phase distortion and self-focusing effects will be caused, and there will be no good spot output. In severe cases, crystals and components will be damaged. The present invention improves the amplification efficiency by adding two additional passes to the double-pass amplification in the existing technical solution; and uses an image transfer structure in conjunction with a spatial light modulator in the additional two passes to compensate for the thermally induced wavefront phase distortion of the side pump module under high repetition rate and high average power operation; in the additional two passes, materials with negative nonlinear refractive index can also be added to compensate for the nonlinear phase accumulated during the high energy amplification of the picosecond laser. And wavefront phase compensation and nonlinear phase compensation elements are added in between. On the basis of improving the amplification efficiency of the existing solution, the factors affecting the beam quality in high repetition rate and high energy picosecond amplification are compensated, and the final beam quality is optimized. The device has a simple and stable structure and is easy to adjust. It can fully extract the energy of the laser gain medium and optimize the beam quality of the high energy and high power picosecond laser amplification output.

[0083] The laser side pump four-pass amplifier, the amplification method and the device thereof of the present invention can be used as a high beam quality and high efficiency picosecond side pump amplifier for compensating for thermally induced wavefront phase distortion and nonlinear self-focusing in the process of picosecond laser high energy amplification, by adding two additional passes to the double-pass amplification to improve the amplification efficiency; and in the additional two passes, an image transfer structure is used in conjunction with a spatial light modulator to compensate for the thermally induced wavefront phase distortion of the side pump module under high repetition rate and high average power operation; in the additional two passes, a material with a negative nonlinear refractive index can also be added to compensate for the nonlinear phase accumulated in the process of picosecond laser high energy amplification. And wavefront phase compensation and nonlinear phase compensation elements are added between them, and on the basis of improving the amplification efficiency, the factors affecting the beam quality in high repetition rate and high energy picosecond amplification are compensated, and the final beam quality is optimized. The device has a simple and stable structure and is easy to adjust, and can fully extract the energy of the laser gain medium and optimize the beam quality of the high energy and high power picosecond laser amplification output.

[0084] Compared with the prior art, the laser side-pump four-way amplifier, the amplification method and the device thereof of the present invention can have but are not limited to the following beneficial effects:

[0085] 1. The present invention utilizes the polarization characteristics of laser to modulate the polarization of the light beam, allowing the light beam to pass through the gain medium four times to complete four-pass amplification. Compared with single-pass and double-pass amplification, the efficiency of extracting energy stored in the gain medium by the seed light is increased to the greatest extent.

[0086] 2. The installed spatial light modulator compensates for the wavefront distortion that occurs during the amplification process of the laser in the side pump module, and the nonlinear crystal alleviates the self-focusing effect of the light beam to ensure good laser output.

[0087] 3. The structure is simple and clear, and debugging is convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, wherein:

[0089] Figure 1 A schematic diagram of a four-way amplifier of a picosecond side pump according to Example 1 of the present invention is shown.

[0090] Figure 2 A schematic diagram of a four-way amplifier of a picosecond side pump according to Example 2 of the present invention is shown.

[0091] Description of reference numerals:

[0092] A. Laser module; B. Isolation module; C. Side pump module; D1. First image transfer module; D2. First image transfer module; E1. First nonlinear crystal module; E2. Second nonlinear crystal module; F1. First reflection module; F2. Second reflection module; 1. Picosecond laser; 2. First thin film polarizer; 3. Second thin film polarizer; 4. Optical isolator; 5. Third thin film polarizer; 6. Quarter wave plate; 7. Side pump module crystal; 8-1. First convex lens; 8-2. First vacuum tube; 8-3. Second convex lens; 9. Faraday rotator; 10. First nonlinear crystal; 11. First 0° space reflector or spatial light modulator; 12. Transfer beam reflector; 13-1. Third convex lens; 13-2. Second vacuum tube; 13-3. Fourth convex lens; 14. Second nonlinear crystal; 15. Second 0° space reflector or spatial light modulator; 16. Fourth thin film polarizer; 17. Fifth thin film polarizer. DETAILED DESCRIPTION

[0093] The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings. However, it should be understood that these embodiments are only used for more detailed and specific description and should not be understood as limiting the present invention in any form.

[0094] This section generally describes the materials and test methods used in the experiments of the present invention. Although many materials and operating methods used to achieve the purpose of the present invention are well known in the art, the present invention is still described as detailed as possible. It is clear to those skilled in the art that in the context, if not specifically stated, the materials and operating methods used in the present invention are well known in the art.

[0095] Example 1

[0096] This embodiment is an exemplary description of the four-way amplifier of the picosecond side pump of the present invention.

[0097] See also Figure 1The four-way amplifier of the picosecond side pump includes: a laser module A, an isolation module B, a side pump module C, a first image transfer module D1, a first image transfer module D2, a first nonlinear crystal module E1, a second nonlinear crystal module E2, a first reflection module F1, and a second reflection module F2; a picosecond laser 1, a first thin-film polarizer 2, a second thin-film polarizer 3, an optical isolator 4, a third thin-film polarizer 5, a quarter-wave plate 6, a side pump module crystal 7, a first convex lens 8-1, a first vacuum tube 8-2, a second convex lens 8-3, a Faraday rotator 9, a first nonlinear crystal 10, a first 0° space reflector or a spatial light modulator 11, a transmission beam reflector 12, a third convex lens 13-1, a second vacuum tube 13-2, a fourth convex lens 13-3, a second nonlinear crystal 14, and a second 0° space reflector or a spatial light modulator 15. The reflection angle of the transmission beam reflector 12 in this embodiment is 34.4°.

[0098] The picosecond laser 1 emits light which is reflected by the first thin-film polarizer 2 and the second thin-film polarizer 3 and then enters the optical isolator 4, and the S-polarized light is converted into P-polarized light.

[0099] Among them, this embodiment is based on a picosecond laser with a repetition frequency of 1kHz, an energy of 0.4mJ, a pulse width of about 60ps, and a central wavelength of 1064nm. The side pump module uses an Nd:YAG side pump module crystal. The optical isolator 4 is composed of a thin film polarizer, a Faraday rotator and a half-wave plate, which are used to block the return light caused by thermal depolarization of the side pump module during operation. After the P-polarized light passes through the Faraday rotator, the polarization will rotate 45° clockwise, and then after passing through the half-wave plate, it will rotate another 45° in the same direction, and then become S-polarized light.

[0100] The seed light passes through the third thin-film polarizer 5 from the optical isolator 4 and then passes through the quarter-wave plate 6. The seed light will become circularly polarized light, reducing the nonlinear effect in the amplification process, because the nonlinear effect of circularly polarized light is about 1.5 times weaker than that of linearly polarized light, in order to obtain a better light spot. Then it enters the Nd:YAG side pump module crystal 7. After the first amplification, the amplified seed light passes through the first image transfer module 8, which is composed of the first convex lens 8-1, the first vacuum tube 8-2 and the second convex lens 8-3. This is used to prevent the seed light from ionizing the air when it is focused in the air, and a small hole is installed in the vacuum tube to perform spatial filtering on the light spot. The upper structure of the vacuum tube is used to connect the vacuum pump to evacuate the tube to 10 -3 -10 -4Pa. After passing through the Faraday rotator 9, it passes through 10 and the first nonlinear crystal to compensate for the self-focusing effect of the light beam, and then it will be reflected into the side pump module by the first 0° spatial reflector or spatial light modulator 11. In this embodiment, the first 0° spatial reflector is used to complete the second amplification. Since the polarization state of the light beam that has completed the second amplification by passing through the quarter-wave plate 6 back and forth is converted from P polarization to S polarization, it passes through the third thin-film polarizer 5 and the transmission beam reflector 12 and enters the second image transmission module 13, which is also composed of two convex lenses and a vacuum tube. (Because of the image transfer module, the spot distribution near the center of the crystal will be imaged to the 0-degree mirror position. Placing a deformable mirror or a spatial light modulator at this position can directly compensate for the wavefront phase distortion caused by thermal distribution at the crystal position) After that, it is reflected by the second 0° spatial reflector or spatial light modulator 15. In this embodiment, the second 0° spatial reflector is used, and it returns along the original route, passes through the second image transfer module 13, the beam transfer reflector 12, the third thin-film polarizer 5, the quarter-wave plate 6, and enters the Nd:YAG side pump module crystal 7 again to enter the third magnification. It is then reflected by the first 0° spatial reflector or spatial light modulator 11 and enters the Nd:YAG side pump module crystal 7 for the fourth magnification. In this embodiment, the first 0° spatial reflector is used, and finally the light beam that has been magnified four times is transmitted from the third thin-film polarizer 5.

[0101] When the seed light with an input energy of 0.4mJ is amplified by a single 5mm Nd:YAG side pump module crystal, a single pulse laser output of 10.6mJ can be obtained.

[0102] Among them, the angle of the quarter-wave plate is precisely adjusted to make the incoming seed light as close to circularly polarized light as possible, so as to reduce the nonlinear effect of the light beam during the amplification process. The image transfer module is composed of two plano-convex lenses with the same focal length. The second lens is mounted on a translation stage to adjust the size and shape of the imaging spot, and the distance between the lens and the module, and between the lenses should be appropriately adjusted. In the first image transfer module 8 in the example, the distance from the first lens to the middle of the module is strictly equal to the focal length of the first lens. The inventor uses a plano-convex lens with f=150mm, so the distance between them is about 150mm. The distance between the two lenses is adjusted by adjusting the front and back of the translation stage to make the imaged light spot close to collimation. A vacuum tube is installed between the two lenses, and a small hole with dual-axis adjustment is installed in the vacuum tube to filter and block the light spots reflected due to the low lens coating.

[0103] Among them, the nonlinear crystal has a negative nonlinear refractive index, which is used to compensate for the self-focusing effect of the light beam and obtain a good output light spot.

[0104] Example 2

[0105] This embodiment is another exemplary description of the four-way amplifier of the picosecond side pump of the present invention.

[0106] like Figure 2 As shown, in this embodiment, the light beam transmission between the isolation module of the four-way amplifier and the second image transmission module is completed through the fourth thin film polarizer 16, the fifth thin film polarizer 17 and the transmission light beam reflector 12. The reflection angle of the transmission light beam reflector 12 in this embodiment is 45°. The first reflection module F1 and the second reflection module F2 use spatial light modulators, and the rest is the same as in Embodiment 1.

[0107] Similarly, when the seed light with an input energy of 0.5 mJ is amplified by a single 5 mm Nd:YAG side pump module crystal, a single pulse laser output of 13.1 ± 0.2 mJ can also be obtained.

[0108] Although the effects of some embodiments are shown above, those skilled in the art should understand that according to the concept of the present invention, the aforementioned other embodiments without specific effects or other technical solutions of the present invention not shown in the embodiments can also achieve the following technical effects stated in the invention content section that are equivalent to the embodiments:

[0109] 1. The present invention utilizes the polarization characteristics of laser to modulate the polarization of the light beam, allowing the light beam to pass through the gain medium four times to complete four-pass amplification. Compared with single-pass and double-pass amplification, the efficiency of extracting energy stored in the gain medium by the seed light is increased to the greatest extent.

[0110] 2. The installed spatial light modulator compensates for the wavefront distortion that occurs during the amplification process of the laser in the side pump module, and the nonlinear crystal alleviates the self-focusing effect of the light beam to ensure good laser output.

[0111] 3. The structure is simple and clear, and debugging is convenient.

[0112] Although the present invention has been described to a certain extent, it is obvious that appropriate changes in various conditions can be made without departing from the spirit and scope of the present invention. It is understood that the present invention is not limited to the embodiments described, but belongs to the scope of the claims, which includes equivalent replacements of each factor described.

Claims

1. A laser side-pumped four-way amplifier, It is characterized in that The laser side pump four-way amplifier comprises: A laser module for outputting laser light; Side pump module for laser amplification; Isolation module for changing laser polarization and blocking the return light caused by thermal depolarization effect of the side pump module; An image transfer module for completely transferring the light spot; Nonlinear crystal modules for compensating for beam self-focusing effects; and A reflection module for reflecting the laser light amplified by the side pump module and then passing it through the side pump module again for a second amplification; in: The image transmission module includes a first image transmission module and a second image transmission module; The nonlinear crystal module includes a first nonlinear crystal module and a second nonlinear crystal module; The reflection module includes a first reflection module and a second reflection module.

2. The laser side-pumped four-way amplifier according to claim 1, Features: The output end of the laser module is connected to the input end of the isolation module; One of the output ends of the isolation module is connected to the input end of the side pump module, the output end of the side pump module is connected to the input end of the first image transfer module, the output end of the first image transfer module is connected to the input end of the first nonlinear crystal module, and the output end of the first nonlinear crystal module is connected to the output input end of the first reflection mode; and / or Another path of the output end of the isolation module is connected to the input end of the second image transmission module through a transmission beam reflector and / or a transmission beam thin film polarizer, the output end of the second image transmission module is connected to the input end of the second nonlinear crystal module, and the output end of the second nonlinear crystal module is connected to the output input end of the second reflection module; Preferably, the reflection angle of the transmission light beam reflector is 30-45°, more preferably 34.4-45°.

3. The laser side-pumped four-way amplifier according to claim 1 or 2, It is characterized in that The isolation module includes an optical isolator and a thin film polarizer; wherein, The optical isolator comprises in sequence: a thin film polarizer of the optical isolator, a Faraday rotator and a half-wave plate of the optical isolator; The thin film polarizer is coated on both sides, one side is coated with a polarizing film with an incident angle of 55.6°, and the other side is coated with an anti-reflection film; The number of the thin film polarizers is 3 to 5, preferably 3 to 4, most preferably 3; and / or The picosecond laser emits P-polarized laser light, and after passing through the optical isolator, the P-polarized laser light is converted into S-polarized laser light; Preferably, at a wavelength of 1064 nm, the polarizing film satisfies an extinction ratio greater than 1000:1, and the antireflection film has a HT>99%; and / or Preferably, at least one thin-film polarizer is arranged after the optical isolator.

4. The laser side-pumped four-way amplifier according to any one of claims 1 to 3, It is characterized in that The side pump module includes a side pump module crystal; wherein, The side pump module crystal is a Nd:YAG side pump module crystal or a Nd:YLF side pump module crystal, and the most preferred one is a Nd:YAG side pump module crystal; The shape of the side pump module crystal is a round rod or a long strip, and the most preferred shape is a round rod; The side and both ends of the side pump module crystal are coated with a film; wherein the wavelength of the film on the side is 808-888nm, preferably 818-868nm, and most preferably 808nm; the wavelength of the film on both ends is 1000-1100nm, preferably 1020-1080nm, and most preferably 1064nm; and / or The pumping mode of the side pump module is end pumping and / or side pumping, and the most preferred mode is side pumping; Preferably, a quarter wave plate for converting linearly polarized laser light into circularly polarized laser light is further included before the side pump module crystal; and / or Preferably, the light transmittance of the film is greater than 90%, more preferably greater than 95%, and further preferably greater than 99.99%.

5. The laser side-pumped four-way amplifier according to any one of claims 1 to 4, It is characterized in that The first image transmission module and the second image transmission module both include: a convex lens and a vacuum tube; A small hole with biaxial adjustment is installed at the focus of the vacuum tube; The convex lens is a plano-convex lens or a bi-convex lens, and is most preferably a plano-convex lens; The number of the convex lenses is 1 to 4, preferably 2 to 3, and most preferably 2; and / or The convex lenses have the same focal length and are confocal; Preferably, when the number of the convex lenses is 2, The first image transmission module and the second image transmission module further include: a first convex lens, a vacuum tube and a second convex lens, wherein the vacuum tube is located between the first convex lens and the second convex lens; and / or The second convex lens is mounted on the translation stage.

6. The laser side-pumped four-way amplifier according to any one of claims 1 to 5, Features: The first nonlinear crystal module comprises: a Faraday rotator and a nonlinear crystal; and / or The second nonlinear crystal module includes a nonlinear crystal; Preferably, the nonlinear crystal has a negative nonlinear refractive index.

7. The laser side-pumped four-way amplifier according to any one of claims 1 to 6, It is characterized in that The first reflection module and the second reflection module both include: a spatial reflection mirror and / or a spatial light modulator; Preferably, the spatial light modulator is selected from one or more of the following: liquid crystal spatial light modulator, electro-optical spatial light modulator, magneto-optical spatial light modulator, acousto-optical spatial light modulator, thermo-optical spatial light modulator, more preferably selected from one or more of the following: liquid crystal spatial light modulator, electro-optical spatial light modulator, magneto-optical spatial light modulator, most preferably a liquid crystal spatial light modulator; Preferably, the reflection angle of the space reflector is 0-5°, most preferably 0°; and / or Preferably, the space reflectors are all coated, and the reflectivity of the coating is more preferably greater than 95%, further preferably greater than 98%, and even more preferably greater than 99%.

8. The laser side-pumped four-way amplifier according to any one of claims 1 to 7, It is characterized in that The laser module includes a laser, and the laser is preferably a picosecond laser; The pulse width of the picosecond laser is preferably 10 to 800 ps, ​​more preferably 20 to 500 ps, ​​further preferably 30 to 100 ps, ​​and most preferably 60 ps.

9. A laser amplification method, It is characterized in that The laser amplification method comprises using a laser side-pumped four-pass amplifier as claimed in any one of claims 1 to 8; Preferably, the amplification method includes: the laser module emits P-polarized laser light, which is converted into S-polarized laser light through the thin-film polarizer and the optical isolator in sequence, and then is transmitted through the thin-film polarizer located behind the optical isolator and converted into circularly polarized laser light through the quarter-wave plate, and then enters the side pump module for the first amplification; the amplified light beam passes through the first image transfer module and the first nonlinear crystal module in sequence, is reflected by the first reflection module, and then passes through the first nonlinear crystal module and the first image transfer module again to enter the side pump module for the second amplification; since the seed light passes through the quarter-wave plate twice, the P polarization is converted into S polarization; then, the light beam passes through the thin-film polarizer located behind the optical isolator, the transmission beam thin-film polarizer and / or the transmission beam reflector used to connect the isolation module and the second image transfer module, the second image transfer module, and the second nonlinear crystal module in sequence, and then is reflected by the second reflection module and then returns to the side pump module along the original path for the third amplification; then, the light beam passes through the first image transfer module and the first nonlinear crystal module in sequence, is reflected by the first reflection module, and then returns to the side pump module along the original path for the fourth amplification; the laser light is converted from S polarization to P polarization again, and finally is transmitted out from the thin-film polarizer located behind the optical isolator.

10. A pulse laser device, It is characterized in that The pulse laser device comprises a laser side-pump four-way amplifier as claimed in any one of claims 1 to 8; Preferably, the pulse laser device is a picosecond pulse laser device.

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