A high-energy ultrafast laser amplification system and a design method thereof

Abstract

The application provides a high-energy ultrafast laser amplification system and a design method thereof. The physical characteristics of the self-focusing phenomenon are utilized, a self-focusing component is designed to expand the spot diameter, the focus position of the self-focusing is ensured to be outside the laser crystal, and the damage inside the laser crystal is avoided. In addition, by determining the parameters of the seed light source, the laser crystal and the pump light source first, and then backstepping the parameters of the beam expander, the design of the entire system can be conveniently and quickly completed, repeated adjustment of various devices and repeated experimental tests are avoided, and the design and manufacturing efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to an ultra-short pulse laser amplifier, in particular to a high-energy ultrafast laser amplification system and a design method thereof. BACKGROUND

[0002] High-energy ultrafast laser has been widely used in laser processing, precision measurement, scientific research and other fields due to its extremely high peak power and ultra-short pulse width. In order to improve the laser output energy, it is often amplified by a multi-stage amplification system. However, with the increase of the number of amplification stages and the increase of laser energy, the self-focusing effect becomes more and more obvious.

[0003] Self-focusing is a nonlinear effect mainly caused by Kerr effect. Under the action of high peak power of ultrafast laser, the refractive index of the gain medium will change nonlinearly with the light intensity distribution, showing a center-high and edge-low nonlinear change, so that the medium is equivalent to a positive lens, resulting in continuous convergence of the light beam inside the medium. The reduction of the beam radius caused by the self-focusing effect will increase the light intensity of the beam, thereby further enhancing the effect of Kerr lens. This convergence will cause the local power density to rise sharply, which not only leads to the distortion of the beam wavefront and reduces the output beam quality, but also easily causes optical damage to the gain medium.

[0004] Therefore, how to solve the above problems existing in the prior art has become the research subject of the present application. SUMMARY

[0005] The purpose of the present application is to provide a high-energy ultrafast laser amplification system and a design method thereof. By reasonably designing the related parameters of the self-focusing suppression component, the focal point of self-focusing is located outside the crystal, thereby avoiding the damage of the laser crystal.

[0006] To achieve the above purpose, the technical scheme adopted by the present application is as follows: a design method of a high-energy ultrafast laser amplification system, comprising the following steps:

[0007] S1. According to the output target of the laser amplification system, the specifications of the seed light source, the laser crystal and the pump light source are determined, and the seed light source, the self-focusing suppression component, the laser crystal and the pump light source are sequentially arranged to form the laser amplification system, wherein the self-focusing suppression component comprises a beam expander;

[0008] S2. According to the laser crystal material used in the laser amplification system, the linear refractive index and the nonlinear refractive index of the crystal material are determined, and the self-focusing threshold power of the crystal is calculated by the formula , wherein λ is the wavelength of the laser;

[0009] S3. According to the length determining the minimum position of the self-focusing focal point of the laser in the crystal when the laser propagates in the crystal , the minimum position satisfying , wherein is a preset safety margin

[0010] S4. presetting a single pulse peak power in the laser crystal and a target beam quality factor , the single pulse peak power estimated according to the final output laser single pulse peak power, and the target beam quality factor determined according to the overall beam quality requirement

[0011] S5. combining the self-focusing threshold power obtained in step S2 , the minimum focal point position determined in step S3 , and the single pulse peak power and the target beam quality factor preset in step S4 to establish a constraint relationship by a formula transformation to deduce the spot radius incident to the laser crystal , and further to obtain the incident spot diameter , wherein is the focal point position, and the focal point position is counted from the incident end surface of the crystal

[0012] S6. according to the incident spot diameter obtained in step S5 , combining the original spot diameter of the seed laser , determining the expansion coefficient of the expander ;

[0013] S7. according to the expansion coefficient determined in step S6 , selecting the corresponding expander optical parameters, so that the seed laser is expanded by the expander to obtain the incident spot diameter meeting the requirements of step S5.

[0014] Further technical solutions, in step S3 , the value range of the preset safety margin is 10-30mm.

[0015] Further technical solutions, the expander is a Galilean expander, the expander includes a negative lens and a positive lens, the focal lengths of the negative lens and the positive lens satisfy , wherein is the expansion coefficient, is the focal length of the negative lens, is the focal length of the positive lens, and the distance between the negative lens and the positive lens .

[0016] Further technical solutions, the self-focusing inhibition component further comprises a diverging lens, and the design method further comprises:

[0017] S7. A diverging lens is added between the beam expander and the laser crystal to expand the divergence angle of the light beam, the distance between the diverging lens and the laser crystal is much smaller than the Rayleigh length of the laser beam, and the focal length of the diverging lens is determined according to experiments.

[0018] Further technical solutions, the self-focusing inhibition component further comprises a soft-edge pinhole diaphragm, and the design method further comprises:

[0019] S8. A soft-edge pinhole diaphragm is added between the beam expander and the diverging lens to suppress the high-order mode components in the light beam, the pinhole aperture of the soft-edge pinhole diaphragm is 1.8-2.2 times the spot diameter of the light beam, and the edge transition width of the soft-edge pinhole diaphragm is 10-20% of the pinhole aperture, and the edge transition adopts a Gaussian or super-Gaussian decay curve.

[0020] According to the second aspect of the present application, a high-energy ultrafast laser amplification system is provided, comprising a seed light source, a self-focusing inhibition component, a laser crystal and a pump light source arranged coaxially in sequence, and the specification parameters of the seed light source, the self-focusing inhibition component, the laser crystal and the pump light source are determined according to the design method of the high-energy ultrafast laser amplification system.

[0021] Further technical solutions, the system further comprises a coupling amplifier, the coupling amplifier is arranged between the laser crystal and the pump light source, and is used for realizing amplification of the pump laser.

[0022] Further technical solutions, the system further comprises a dichroic mirror, the seed light source, the self-focusing inhibition component and the laser crystal are arranged on one side of the dichroic mirror, the coupling amplifier and the pump light source are arranged on the other side of the dichroic mirror, the laser beam emitted by the seed light source is injected into the laser crystal after passing through the self-focusing inhibition component, the pump laser emitted by the pump light source is amplified by the coupling amplifier and then passes through the dichroic mirror to be injected into the laser crystal to realize amplification of the seed laser, and the amplified seed laser is reflected by the dichroic mirror and output.

[0023] ​According to a third aspect of the present invention, a high-energy ultrafast laser amplification system is also provided, comprising a seed source and at least two amplification units. Each amplification unit includes a self-focusing suppression component, a laser crystal, and a pump source. The specifications of the self-focusing suppression component, the laser crystal, and the pump source of each amplification unit are determined according to the design method of the high-energy ultrafast laser amplification system described above. The laser emitted by the seed source is transmitted between the amplification units through a mirror and is amplified by the multiple amplification units before being output.

[0024] A further technical solution involves the preset laser crystal single-pulse peak power of each amplification unit in this system. and target beam quality factor Increasing step by step.

[0025] The high-energy ultrafast laser amplification system and its design method provided in this application have the following technical advantages:

[0026] By utilizing the physical properties of self-focusing, a self-focusing suppression component is designed to increase the spot diameter, ensuring that the focal point of self-focusing falls outside the laser crystal and avoiding damage to the laser crystal's interior. Furthermore, by first determining the parameters of the seed source, laser crystal, and pump source, and then working backwards to deduce the beam expander parameters, the entire system design can be completed quickly and easily, avoiding repeated adjustments to individual components and numerous experimental tests, thus improving design and manufacturing efficiency. Attached Figure Description

[0027] Appendix Figure 1 This is a simplified flowchart of the design method for a high-energy ultrafast laser amplification system according to an embodiment of the present invention;

[0028] Appendix Figure 2 This is a schematic diagram of a high-energy ultrafast laser amplification system (with beam expander) corresponding to Embodiment 1 of the present invention.

[0029] Appendix Figure 3 This is a schematic diagram of the high-energy ultrafast laser amplification system (with diverging lens) corresponding to Embodiment 2 of the present invention.

[0030] Appendix Figure 4 This is a schematic diagram of the high-energy ultrafast laser amplification system (with soft-edge aperture) corresponding to Embodiment 3 of the present invention.

[0031] Appendix Figure 5 The laser beam profile and analysis diagram obtained without using the self-focusing suppression component;

[0032] Appendix Figure 6 The laser beam profile and analysis diagram obtained in Example 3;

[0033] Appendix Figure 7The schematic diagram of the high-energy ultrafast laser amplification system of the fourth embodiment of the present application (with a coupling amplifier);

[0034] The schematic diagram of the high-energy ultrafast laser amplification system of the fourth embodiment of the present application (with a coupling amplifier); Figure 8 The schematic diagram of the high-energy ultrafast laser amplification system of the fifth embodiment of the present application (with a dichroic mirror);

[0035] The schematic diagram of the high-energy ultrafast laser amplification system of the fourth embodiment of the present application (with a coupling amplifier); Figure 9 The schematic diagram of the high-energy ultrafast laser amplification system of the fourth embodiment of the present application (with a coupling amplifier);

[0036] In the above figures: 1. seed light source; 2. beam expander; 21. negative lens; 22. positive lens; 3. diverging lens; 4. soft-edge pinhole diaphragm; 5. laser crystal; 6. pump light source; 7. coupling amplifier; 8. dichroic mirror; 9. reflecting mirror; 10. first-stage amplification unit; 11. second-stage amplification unit. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0038] As to the "first", "second", etc. used herein, they do not mean to particularly indicate the order or sequence, nor to limit the present application. They are merely used to distinguish components or operations described by the same technical terms.

[0039] As to the "connection" or "positioning" used herein, it can mean that two or more components or devices are in direct physical contact with each other or in indirect physical contact with each other, or it can mean that two or more components or devices operate or act with each other.

[0040] As to the "contain", "include", "have" and the like used herein, they are all open terms, that is, they mean to include but are not limited to.

[0041] As to the "front", "back", "up", "down", "left", "right" and the like used herein, they are all directional words, which in the present application are merely used to describe the positional relationship between structures, and are not used to limit the protection scheme and the specific direction in actual implementation.

[0042] Figure 1 The laser beam spot diagram output by the existing laser amplification system is shown, and from the figure, it can be seen that there are multiple self-focusing beam filamentation phenomena.

[0043] Embodiment one: In this embodiment, the target laser output is a single pulse energy of 1.5 mJ, a pulse width of 10 ps, and a beam quality factor of 1.1. The design and construction process of a high-energy ultrafast laser amplification system is described in detail. Please refer to Figure 1 and Figure 2 wherein Figure 1 is a brief flowchart of the design method corresponding to embodiment one, Figure 2 is a structural diagram of the amplification system obtained by the design method of embodiment one.

[0044] Step S1: Preliminary determination of system device parameters.

[0045] First, according to the output target, the specification parameters of the seed light source 1, the laser crystal 5, and the pump light source 6 are determined. Since these devices are usually subject to conditions such as cost and size, the specification parameters of these devices are determined in priority according to the actual situation.

[0046] In this embodiment, the seed light source 1 is a fiber seed source with an output spot diameter of 0.8 mm. The output laser center wavelength matches the gain wavelength of the laser crystal 5, the initial beam quality factor is about 1.05, and the laser wavelength λ is 1064 nm.

[0047] The laser crystal 5 is a neodymium-doped yttrium vanadate crystal (Nd:YVO4) ), which has a high gain coefficient and good thermal stability at a wavelength of 1064 nm. The crystal length is set to 18 mm, and the cross-sectional size is 3 mm x 3 mm to meet the pumping light absorption and beam transmission requirements.

[0048] The pump light source 6 is a 115 W semiconductor laser pump source, and the output wavelength is selected to be 808 nm, 878 nm, or 888 nm. The pump method is end-pumping, wherein the pump light source 6 can focus the pump light to the input end face of the laser crystal 5 through a coupling lens group.

[0049] The self-focusing suppression assembly is used to suppress the self-focusing effect. In this embodiment, the self-focusing suppression assembly includes a beam expander 2, which is arranged between the seed light source 1 and the laser crystal 5, and is used to adjust the spot size of the light incident on the laser crystal 5. By increasing the spot size, it is ensured that the focal point of self-focusing is located outside the laser crystal 5, thereby avoiding damage to the laser crystal 5.

[0050] The seed light source 1, the beam expander 2, the laser crystal 5, and the pump light source 6 are sequentially arranged in order to preliminarily form a high-energy ultrafast laser amplification system. The specification parameters of the beam expander 2 are determined by subsequent steps.

[0051] Step S2: Calculate the self-focusing threshold power of the laser crystal 5.

[0052] For the selected crystal, the following parameters are obtained by Material Parameter Handbook and experimental test: linear refractive index is 1.96; nonlinear refractive index is about .

[0053] According to the formula for calculating the self-focusing threshold power

[0054]

[0055] The self-focusing threshold power is calculated as .

[0056] It should be noted that there is no unique general formula for the self-focusing threshold power. The formula used in this embodiment is the threshold power formula for a long pulse width Gaussian beam propagating in a bulk medium. The threshold power of a short pulse laser is usually higher than this value. Therefore, when the value calculated by this formula can make the self-focusing focal point outside the crystal, the actual threshold power must make the self-focusing focal point outside the crystal. Therefore, the value calculated by this formula can be used instead of the actual self-focusing threshold power for subsequent estimation.

[0057] Step S3: Determine the minimum position of the self-focusing focal point.

[0058] According to the length of the selected crystal , the minimum position of the self-focusing focal point when the laser propagates in the crystal is determined , which satisfies , wherein is a preset safety margin;

[0059] Since the light pulse has a certain waveform, the front, center and trailing edge of each part are not only different in intensity, but also different in time through the medium. When working in quasi-steady state, the size of the refractive index of the light pulse in the medium is determined by the intensity of the light at that time. Since different parts of the light pulse pass through the medium at different times, the difference in refractive index between the center and the edge of the beam cross section also varies with the time of the light beam passing through the medium. The consequence is that the light beams passing through the medium at different times, although belonging to the same light pulse, are self-focused at different positions, looking like a thin filament.

[0060] Therefore, a certain safety margin needs to be left to ensure that the self-focusing focal points of light beams at different times are all outside the laser crystal 5. However, the safety margin cannot be infinite, because the spot size is limited by the cross-sectional size of the laser crystal 5, and the corresponding self-focusing focal point also cannot be infinitely far away. After comprehensive consideration, the preset safety margin is preferably in the range of 10-30 mm.

[0061] In this embodiment, the length L of the laser crystal 5 is known to be 18 mm, and a safety margin is preset Take 20 mm.

[0062] According to the minimum focal position satisfying the relationship:

[0063]

[0064] Substitute the data to calculate:

[0065]

[0066] That is, the self-focusing focal point needs to be at least located at 38 mm from the front end of the crystal.

[0067] Step S4: preset single pulse peak output power and target beam quality factor.

[0068] Single pulse peak output power Refers to the maximum single pulse power input into the laser crystal 5, which can be estimated according to the single pulse energy to be output and the pulse width, and the single pulse peak output power of the seed laser after being amplified by the laser crystal 5 .

[0069] Target beam quality factor According to the output requirement, it is preset to be 1.1.

[0070] Step S5: derive the spot diameter incident to the laser crystal 5.

[0071] The following self-focusing focal point position calculation formula is used in this embodiment to deduce the spot diameter:

[0072] ;

[0073] Wherein, is the focal position, counted from the incident end of the laser crystal 5.

[0074] is the spot radius incident to the laser crystal 5, and the incident spot radius The larger the focal position is farther.

[0075] λ is the wavelength of the laser, is the beam quality factor, used to reflect the strength of diffraction to correct the deviation between the actual laser and the ideal Gaussian beam (B ).

[0076] is the single pulse peak output power, is the self-focusing threshold power. In theory, when , self-focusing will occur. For reflecting the strength of self-focusing, the greater the value, the stronger the self-focusing trend, and the closer the focus position.

[0077] Substitute , , λ = 1064 nm, , the calculated , the incident spot diameter .

[0078] Step S6: the beam expander 2 expansion coefficient is determined.

[0079] According to the calculated incident spot diameter , combined with the original spot diameter of the seed laser , the beam expander 2 .

[0080] In this embodiment, the original spot diameter is 0.8mm, and the beam expander 2 with a 1:1.4 expansion ratio is used to expand the spot to a spot with a diameter of 1.12mm, and the self-focusing focus position is about 38mm away from the incident surface of the laser crystal 5.

[0081] S7. According to the expansion coefficient determined in step S6, the corresponding optical parameters of the beam expander 2 are selected.

[0082] The beam expander 2 has many kinds, and the simplest concave lens can also achieve the expansion effect, but using a concave lens as a beam expander 2 will cause the beam divergence angle to increase, the wavefront distortion to intensify, and the parallelism of the expanded beam to be very poor, which cannot meet the requirements of high-precision optical systems for beam collimation.

[0083] The beam expander 2 can also be a Keplerian beam expander or a Galilean beam expander. When a Keplerian beam expander is used, the expansion coefficient , wherein , are the focal lengths of the two positive lenses in the beam expander, and the overall length of this type of beam expander is relatively long. When a Galilean beam expander is used, the expansion coefficient , wherein is the focal length of the negative lens, is the focal length of the positive lens, and this type of beam expander is more compact in volume.

[0084] In this embodiment, a Galilean beam expander is selected, that is, a negative lens 21 is matched with a positive lens 22, the focal lengths of the negative lens 21 and the positive lens 22 satisfy , and the distance between them is to ensure the collimation characteristics of the expanded beam. Compared with directly using a negative lens, the Galilean beam expander has smaller aberration, smaller high-order mode, and higher beam quality.

[0085] According to the foregoing calculation results, in combination with the size limitation of the laser, the focal length of the negative lens 21 is selected as (the negative sign indicates a concave lens), and the focal length of the positive lens 22 is , the center distance between the negative lens 21 and the positive lens 22 is , and the center distance between the positive lens 22 and the laser crystal 5 is .

[0086] Up to now, the design of the high-energy ultrafast laser amplification system is completed. Through the design method, it can be ensured that the focus position of the self-focusing falls outside the laser crystal 5, and the damage of the laser crystal 5 is avoided. In addition, by first determining the parameters of the seed light source 1, the laser crystal 5 and the pump light source 6, and then backstepping the parameters of the beam expander 2, the design of the entire system can be completed conveniently and quickly, and the repeated adjustment of each device and repeated experimental test are avoided, and the design and manufacturing efficiency is improved.

[0087] Example two: Since the high peak power of femtosecond and picosecond pulses may cause thermal lens effect, the additional convergence generated thereby will cause the self-focusing effect to be strengthened, which may exceed the adjustment range of the foregoing design method. Therefore, in this embodiment, a diverging lens 3 is added to the beam expander 2 to form a self-focusing suppression assembly, as shown in Figure 3 The specifications and design methods of the remaining components are consistent with those of example one, and the specific setting methods and effects are as follows:

[0088] After the beam expansion coefficient and the lens parameters of the beam expander 2 are determined, the diverging lens 3 is added between the beam expander 2 and the laser crystal 5, and the distance between the diverging lens 3 and the laser crystal 5 is set to 2 mm, which is much smaller than the Rayleigh length of the laser beam, so as to ensure that only the beam divergence angle is changed without significantly expanding the spot diameter incident to the crystal.

[0089] Since the focusing angle of the self-focusing is influenced by multiple factors such as pulse shape and thermal accumulation, accurate calculation is complex, and the diverging lens 3 is more convenient to replace, so the focal length of the diverging lens 3 is determined by experimental test. By replacing the diverging lens 3 with different focal lengths, the spot uniformity, filamentation phenomenon and beam quality of the laser output are compared, and finally the optimal focal length is selected.

[0090] In this embodiment, it is tested that when the diverging lens 3 with a focal length of -135 mm is selected, the beam divergence angle increases from about 1.5 mrad output from the beam expander 2 to about 3.2 mrad. By increasing the beam divergence angle, the diffraction divergence effect of the beam offsets part of the convergence effect related to the self-focusing, so that the self-focusing focus position is stabilized outside the laser crystal 5, and there is no obvious filamentation phenomenon, which meets the system design requirements.

[0091] In order to ensure that the final output beam quality reaches the output target and reduce the high-order mode caused by the beam expander 2, the embodiment adds a soft-edge aperture stop 4 based on the embodiment two, as shown in the following figure. Figure 4

[0092] In the design, the soft-edge aperture stop 4 is arranged between the beam expander 2 and the diverging lens 3, and the aperture diameter of the soft-edge aperture stop 4 is about 1.8 to 2.2 times the spot diameter, so as to retain the core energy of the fundamental mode and suppress the high-order mode. The edge transition zone width of the soft-edge aperture stop 4 is 10% to 20% of the aperture diameter, and the diffraction effect can be reduced by reasonably designing the width of the edge transition zone. The edge transition zone adopts a Gaussian or super-Gaussian attenuation curve to match the gradient of the light intensity distribution.

[0093] In this embodiment, the spot diameter can be the spot diameter after the beam expansion of the beam expander 2, which is about 1.12 mm, and the aperture diameter of the soft-edge aperture stop 4 is determined to be 2 mm accordingly. The edge transition zone width is set to 0.2 mm, and the transition zone adopts a Gaussian attenuation curve, so that the light intensity smoothly decays from the center to the edge according to the Gaussian law, avoiding the generation of new diffraction high-order modes due to the steep edge of the hard-edge aperture stop.

[0094] Figure 5 The figure shows the laser beam profile and analysis diagram of the laser amplification system without using the self-focusing suppression assembly, which is taken by the BeamGage software. Different colors in the figure represent different light intensities. It can be seen from the figure that there are obvious corrugated and vortex structures in the center and periphery of the spot, the light intensity distribution is uneven, and the beam has a certain phase distortion or filamentation phenomenon.

[0095] Figure 6 The figure shows the laser beam profile and analysis diagram generated by the laser amplification system provided by the embodiment three. It can be seen from the figure that the light intensity transition is smoother, there are no obvious local corrugations or vortices, the overall uniformity is better, the stray light at the periphery of the spot is obviously less, the energy is more concentrated in the central area, and the sidelobe effect is weak, which indicates that the overall beam quality is better than the laser beam shown in the following figure. Figure 5

[0096] It can be seen that by using the combination of the beam expander 2, the diverging lens 3 and the soft-edge aperture stop 4, the self-focusing effect is suppressed, the crystal damage is avoided, and the beam quality of the final output is ensured.

[0097] In the above embodiments, a coupling amplifier 7 can also be arranged according to the actual situation, which is arranged between the laser crystal 5 and the pump light source 6, and is used to realize the amplification and efficient coupling of the pump laser.

[0098] ​​​​In the embodiment, the coupling amplifier 7 uses a 1:5 coupling cylinder to shape the pump spot into an elliptical spot matching the absorption cross section of the laser crystal 5, so that the pump light forms a uniform energy distribution inside the crystal, improves the pump absorption efficiency of the laser crystal 5, and reduces the thermal lens effect caused by uneven pump light distribution.

[0099] Through the above pump amplification design, the laser finally output by the laser crystal 5 meets the target of single pulse energy 1.5 mJ and beam quality factor M² = 1.1.

[0100] Embodiment five: In addition, the above high-energy ultrafast laser amplification system can also include a dichroic mirror 8, the seed light source 1, the self-focusing suppression assembly, the laser crystal 5 is arranged on one side of the dichroic mirror 8, and the coupling amplifier 7 and the pump light source 6 are arranged on the other side of the dichroic mirror 8. The laser beam emitted by the seed light source 1 passes through the self-focusing suppression assembly and then enters the laser crystal 5. The pump laser emitted by the pump light source 6 is amplified by the coupling amplifier 7 and then enters the laser crystal 5 through the dichroic mirror 8, so as to realize amplification of the seed laser. After the seed laser is amplified by the laser crystal 5, it is directly output through the reflection of the dichroic mirror 8 or input into the next stage of amplification system.

[0101] Embodiment six: The embodiment provides a multi-stage high-energy ultrafast laser amplification system, which comprises a seed light source 1 and at least two stages of amplification units. Each stage of amplification unit comprises a self-focusing suppression assembly, a laser crystal 5 and a pump light source 6. The specification parameters of the self-focusing suppression assembly, the laser crystal 5 and the pump light source 6 of each stage of amplification unit are determined according to the design method of the above high-energy ultrafast laser amplification system. The laser emitted by the seed light source 1 is transmitted between the stages of amplification units through a reflector 9 and is output after being amplified by the multi-stage amplification units. The number of stages of amplification units can be inversely deduced according to the output power target and the amplification capacity of the single-stage amplification unit, so as to avoid self-focusing damage caused by excessively high single-stage power and to avoid increasing the complexity of the system by designing too many stages.

[0102] The single pulse peak power of the preset laser crystal 5 of each stage of amplification unit and the target beam quality factor increases stage by stage. Through accurate control of the self-focusing threshold in the stage-by-stage amplification, self-focusing damage caused by excessively high single-stage amplification power is avoided, and through stepwise beam quality optimization, the beam quality meets the standard when high-energy output is finally realized.

[0103] Taking a system comprising two stages of amplification units 11 as an example, if the final output target is single pulse energy 4 mJ and the beam quality is less than 1.5, the single pulse peak power of the first stage of amplification unit 10 It can be designed to have a power output of 80~100MW and a target beam quality factor of 1.1~1.2; the single-pulse peak power of the second-stage amplification unit 11 is increased to about 400MW, and the target beam quality factor is... .

[0104] The first-stage amplification unit 10 can be φ1mm×5mm. With a crystal and a 1.2x beam expander, the second stage can use a φ3mm×15mm lens. The crystal is paired with a 1.5x beam expander. Accordingly, the power of the pump source 6 of each amplification unit and the size of the laser crystal 5 must be matched in an increasing manner: the first-stage amplification unit 10 can use a 20W 808nm pump source, and the second-stage amplification unit 11 is upgraded to a 100W pump source.

[0105] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A design method for a high-energy ultrafast laser amplification system, characterized in that, Includes the following steps: S1. Based on the output target of the laser amplification system, determine the specifications of the seed light source, laser crystal, and pump light source, and set the seed light source, self-focusing suppression component, laser crystal, and pump light source in sequence to form a laser amplification system, wherein the self-focusing suppression component includes a beam expander; S2. Determine the linear refractive index of the laser crystal material used in the laser amplification system. and nonlinear refractive index Through formula The self-focusing threshold power of the crystal was calculated. , where λ is the laser wavelength; S3. Based on the length of the selected crystal. To determine the minimum position of the self-focusing focal point when the laser propagates in the crystal. The minimum position satisfies ,in To pre-set a safety margin, The value range is 10~30mm; S4. Preset the peak power of a single pulse in the laser crystal. and target beam quality factor M 2 The single-pulse peak power Based on the estimated peak power of the final output laser single pulse, the target beam quality factor is... Determined based on overall beam quality requirements; S5. Combining the self-focusing threshold power obtained in step S2 The minimum focal position determined in step S3 And the single-pulse peak power preset in step S4 and target beam quality factor According to the formula for focal position Establish constraint relationships The radius of the incident laser spot can be derived by transforming the formula. Thus, the diameter of the incident light spot is obtained. ,in The focal position is measured from the incident end face of the crystal; S6. Based on the incident light spot diameter obtained in step S5 Combined with the original spot diameter of the seed laser Determine the expansion coefficient of the beam expander. The beam expansion coefficient ; S7. Based on the beam expansion coefficient determined in step S6 Select the corresponding beam expander optical parameters.

2. The design method of the high-energy ultrafast laser amplification system according to claim 1, characterized in that, The beam expander is a Galilean beam expander, comprising a negative lens and a positive lens, the focal lengths of which satisfy the following conditions: ,in, The beam expansion coefficient is... The focal length of the negative lens. The focal length of the positive lens, and the distance between the negative and positive lenses. .

3. The design method of the high-energy ultrafast laser amplification system according to claim 1, characterized in that, The self-focusing suppression component further includes a divergence lens, and the design method further includes: S7. A diverging lens is added between the beam expander and the laser crystal to widen the divergence angle of the beam. The distance between the diverging lens and the laser crystal is much smaller than the Rayleigh length of the laser beam. The focal length of the diverging lens is determined by experimental adjustment.

4. The design method of the high-energy ultrafast laser amplification system according to claim 3, characterized in that, The self-focusing suppression component further includes a soft-edge pinhole aperture, and the design method further includes: S8. A soft-edge pinhole aperture is added between the beam expander and the diverging lens to suppress higher-order mode components in the beam. The aperture of the soft-edge pinhole aperture is 1.8 to 2.2 times the diameter of the beam. The beam diameter; the width of the edge transition zone of the soft-edge aperture is 10% to 20% of the aperture diameter, and the edge transition zone adopts a Gaussian or super-Gaussian attenuation curve.

5. A high-energy ultrafast laser amplification system, characterized in that, The system includes a seed light source, a self-focusing suppression component, a laser crystal, and a pump light source arranged coaxially in sequence. The specifications of the seed light source, the self-focusing suppression component, the laser crystal, and the pump light source are determined according to the design method of the high-energy ultrafast laser amplification system according to any one of claims 1 to 4.

6. The high-energy ultrafast laser amplification system according to claim 5, characterized in that, It also includes a coupling amplifier, which is disposed between the laser crystal and the pump source to amplify the pump laser.

7. The high-energy ultrafast laser amplification system according to claim 6, characterized in that, It also includes a dichroic mirror. The seed light source, the self-focusing suppression component, and the laser crystal are disposed on one side of the dichroic mirror, and the coupling amplifier and the pump light source are disposed on the other side of the dichroic mirror. The laser beam emitted by the seed light source passes through the self-focusing suppression component and then enters the laser crystal. The pump laser emitted by the pump light source is amplified by the coupling amplifier and then passes through the dichroic mirror and is injected into the laser crystal to realize the amplification of the seed laser. After being amplified by the laser crystal, the seed laser is reflected by the dichroic mirror and output.

8. A high-energy ultrafast laser amplification system, characterized in that, It includes a seed light source and at least two amplification units. Each amplification unit includes a self-focusing suppression component, a laser crystal, and a pump light source. The specifications of the self-focusing suppression component, laser crystal, and pump light source of each amplification unit are determined according to the design method described in any one of claims 1 to 4. The laser emitted by the seed light source is transmitted between the amplification units through a reflector and is amplified by the amplification units before being output.

9. The high-energy ultrafast laser amplification system according to claim 8, characterized in that, The single-pulse peak power of the preset laser crystal in each amplification unit and target beam quality factor Increasing step by step.

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