Femtosecond laser pulse string driven atom precipitation method

Abstract

The invention discloses a femtosecond laser pulse string driven atom precipitation method, which relates to the field of laser extreme manufacturing, is realized based on a femtosecond laser micro-nano machining system, and comprises the following steps: fixing an alloy material on a three-dimensional displacement table; the angle of the two-phase color mirror is adjusted, so that the femtosecond laser pulse is vertically incident to the surface of the alloy material; a focus lens is adjusted and machined, and it is guaranteed that laser coaxially and vertically enters; an imaging camera is adjusted, and a laser processing area is monitored in real time through a real-time imaging module; adjusting the beam shaping module to generate a pulse string with a fixed pulse interval; and laser energy is adjusted, array processing of different pulse overlap rates is carried out in a designated area on the surface of the material through cooperative control of a galvanometer system, a three-dimensional displacement table and a mechanical light shutter, and femtosecond laser pulse string driven atom precipitation is completed. According to the method, the laser heating and cooling rate can be flexibly adjusted, low-cost and high-efficiency atomic-scale precipitation and even atomic configuration regulation of different elements of the alloy are achieved, and improvement of the performance of the alloy material is facilitated.

Description

Technical Field

[0001] This invention relates to the field of laser extreme manufacturing, specifically to a method for atomic precipitation driven by femtosecond laser pulse trains. Background Technology

[0002] Developing alloy materials with high strength and ductility is of great significance for improving engineering reliability and energy efficiency. Atomic precipitation strengthening can achieve fine and stable nanoscale phase synthesis, thereby significantly improving these two mutually restrictive properties. Professor George (Yang Y, Chen T, Tan L, et al. Bifunctional nanoprecipitates strengthen and ductilize a medium-entropy alloy[J]. Nature,2021, 595(7866): 245-249.) regulated the transformation of nanoprecipitates from face-centered cubic to body-centered cubic, significantly improving the strength and ductility of Fe-Ni-Al-Ti medium-entropy alloys. Professor Liu (Yang T, Zhao YL, Tong Y, et al. Multicomponent intermetallic nanoparticles and superb mechanical behaviors of complex alloys[J]. Science, 2018, 362(6417): 933-937.) achieved an ultimate tensile strength of 1.5 GPa and a ductility of up to 50% in Al7Ti7 alloys at room temperature through the precipitation of multicomponent intermetallic nanoparticles at a spatial scale of 50 nm. However, both methods used high-temperature followed by cold water quenching to control atomic precipitation, which could not precisely and flexibly control the cooling rate or achieve ultra-fast cooling. Professor Zhong (Zhong L, Wang J, Sheng H, et al. Formation of monatomic metallic glasses through ultrafast liquid quenching[J]. Nature, 2014, 512(7513): 177-180.) achieved 10 14 Ks -1High-speed liquid quenching rates can be used to achieve the glassization of refractory body-centered cubic single metals, but this technology is costly, difficult to manufacture, and has stringent environmental requirements. Professor Colombier (Iabbaden D, Amodeo J, Fusco C, et al. Dynamics of Cu–Zrmetallic glass devitrification under ultrafast laser excitation revealed by atomistic modeling[J]. Acta Materialia, 2024, 263: 119487.) used molecular dynamics simulations to discover that femtosecond lasers can control the quenching rate and drive the formation of the body-centered cubic phase inside Cu-Zr alloys, but this is only a prediction based on numerical simulation methods and has not been experimentally verified. Summary of the Invention

[0003] To address the aforementioned shortcomings in existing technologies, this invention provides a femtosecond laser pulse train-driven atomic precipitation method that can flexibly adjust the laser heating and cooling rates, achieving low-cost, high-efficiency atomic-level precipitation of different elements in alloys and even the control of atomic configurations. This facilitates the improvement of alloy material properties, thereby promoting industrial applications and energy efficiency.

[0004] To achieve the aforementioned objectives, the present invention employs the following technical solution: a femtosecond laser pulse train-driven atomic precipitation method, implemented using a femtosecond laser micro / nano fabrication system, comprising the following steps: S1: Fix the alloy material onto the three-dimensional displacement stage; S2: Adjust the angle of the dichroic mirror so that the femtosecond laser pulse is incident perpendicularly on the surface of the alloy material; S3: Adjust the processing focusing lens to ensure that the laser is coaxially and perpendicularly incident; S4: Adjust the imaging camera to monitor the laser processing area in real time through the real-time imaging module; S5: Adjust the beam shaping module to generate a pulse train with a fixed pulse interval; S6: Adjust the laser energy and, through the coordinated control of the galvanometer system, three-dimensional displacement stage and mechanical optical shutter, perform array processing with different pulse overlap rates in a designated area on the material surface to complete the femtosecond laser pulse train-driven atomic precipitation.

[0005] Furthermore, the femtosecond laser micro-nano fabrication system includes a Ti:sapphire femtosecond laser, a mirror, an energy adjustment module, a beam shaping module, a laser processing module, and a real-time imaging module; The Ti:sapphire femtosecond laser generates femtosecond laser light, which is reflected and propagated by the first and second reflecting mirrors. The energy regulation module includes a half-wave plate and a polarizer. The laser polarization direction is changed by rotating the half-wave plate, and then a fixed-direction polarization is generated by the polarizer to achieve stepless energy regulation. The beam shaping module includes multiple birefringent crystals of different thicknesses, with the optical axes of adjacent crystals at 45°, generating pulse trains with fixed time intervals; The laser processing module includes a mechanical optical shutter, a galvanometer system, a scanning mirror, a collimating mirror, a dichroic mirror, a focusing mirror turntable, a focusing mirror, a sample fixture, and a three-dimensional displacement stage. The mechanical optical shutter controls the switching of the laser by opening and closing, and works with the galvanometer system and the three-dimensional displacement stage to achieve processing with specified parameters. The laser is reflected from the surface of the dichroic mirror and enters the focusing mirror to process the sample surface. The sample is fixed on the three-dimensional displacement stage by the sample fixture to achieve relative movement with the laser. The focusing mirror turntable enables the switching of different magnification focusing mirrors. The real-time imaging module includes a beam splitter, a halogen lamp, an imaging lens group, and an imaging camera. The halogen lamp provides white light illumination, which illuminates the sample surface after passing through the beam splitter, dichroic mirror, and focusing mirror. The reflected light passes through the dichroic mirror, is reflected on the surface of the beam splitter, and enters the imaging lens group. After being focused, it is collected in the imaging camera. The imaging lens group moves the imaging surface by adjusting the lens spacing.

[0006] Furthermore, the thickness of the birefringent crystal in the beam shaping module is selected according to the required pulse train time interval and number of pulses, and the crystal thickness is halved one by one along the laser incident direction.

[0007] Furthermore, the parameters of the femtosecond laser pulse are: pulse width 100 fs, center wavelength 800 nm, and repetition frequency 1 kHz.

[0008] Furthermore, the imaging plane of the imaging camera is adjusted to the same height as the laser focal plane through the imaging lens group.

[0009] Furthermore, the dichroic mirror reflects near-infrared laser light with a center wavelength of 800 nm and transmits imaging white light with a center wavelength of 400 nm–730 nm.

[0010] Furthermore, the pulse overlap rate is achieved by adjusting the scanning speed of the galvanometer system.

[0011] Furthermore, the laser energy is 1.5 mW-50 mW.

[0012] Furthermore, the beam shaping module utilizes the different refractive indices of the two optical axes within the crystal, combined with the crystal thickness, to obtain different pulse delays. The calculation formula is as follows:

[0013] in, For pulse delay, and It has two optical axes, namely Light and Light, The speed of light in a vacuum. The thickness of the crystal; The formula for calculating the refractive index of two optical axes with respect to a specific wavelength of light is:

[0014]

[0015] in, The incident laser wavelength; By adjusting the angle between the optical axis of the birefringent crystal and the polarization of the incident laser, the energy ratio of the two pulses can be flexibly controlled. Based on the vector decomposition of linearly polarized light, the energy ratio along the optical axis can be obtained. Light and perpendicular to the optical axis The light amplitude is:

[0016]

[0017] in, and They are respectively Light and The amplitude of light The angle between the incident laser polarization and the crystal optical axis. The incident laser amplitude; According to the Fresnel amplitude formula, the ratio of the intensities of the two beams is:

[0018] in, and They are respectively Light and The intensity of light.

[0019] The beneficial effects of this invention are: (1) This invention utilizes the flexible and controllable properties of femtosecond lasers. Compared with high-temperature quenching, it can achieve precise selective precipitation and accurate control of processing quality, meet the different requirements of different regions of alloy components, and has the advantages of simple and controllable process, convenient debugging, and favorable for complex working conditions. It can promote the development of new heterogeneous materials.

[0020] (2) This invention utilizes the high energy characteristics of femtosecond lasers to realize the processing and preparation of a variety of alloy materials, and has strong adaptability.

[0021] (3) This invention utilizes the short pulse width characteristics of femtosecond lasers to achieve rapid heating and cooling in a short time, which is highly efficient and low cost.

[0022] (4) The present invention utilizes a birefringent crystal group to achieve flexible beam shaping and obtain a GHz controllable pulse train that repeats at KHz. It is highly flexible, low in cost, and beneficial for low-damage selective segregation. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the femtosecond laser processing system and beam shaping effect of the present invention.

[0024] Figure 2 This is a schematic diagram of the beam shaping module of the present invention.

[0025] Figure 3 This is an elemental distribution diagram of the nickel-based superalloy nanoparticles obtained in Example 1.

[0026] Figure 4 The graph shows the change in Al atomic content with altitude at 230 ps.

[0027] Figure 5 This is an elemental distribution diagram of the nickel-based superalloy nanoparticles obtained in Example 2.

[0028] The components include: 1. Ti:Sapphire femtosecond laser; 2. First reflecting mirror; 3. Half-wave plate; 4. Polarizer; 5. Second reflecting mirror; 6. Mechanical shutter; 7. Beam shaping module; 8. Galvanometer system; 9. Scanning mirror; 10. Collimating mirror; 11. Dichroic mirror; 12. Focusing mirror turntable; 13. Focusing mirror; 14. Sample; 15. Sample fixture; 16. Three-dimensional displacement stage; 17. Beam splitter; 18. Halogen lamp; 19. Imaging lens group; 20. Imaging camera. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] A femtosecond laser pulse train-driven atomic precipitation method, implemented based on a femtosecond laser micro / nano fabrication system, includes the following steps: S1: Fix the alloy material onto the three-dimensional displacement stage; S2: Adjust the angle of the dichroic mirror so that the femtosecond laser pulse is incident perpendicularly on the surface of the alloy material; S3: Adjust the processing focusing lens to ensure that the laser is coaxially and perpendicularly incident; S4: Adjust the imaging camera to monitor the laser processing area in real time through the real-time imaging module; S5: Adjust the beam shaping module to generate a pulse train with a fixed pulse interval; S6: Adjust the laser energy and, through the coordinated control of the galvanometer system, three-dimensional displacement stage and mechanical optical shutter, perform array processing with different pulse overlap rates in a designated area on the material surface to complete the femtosecond laser pulse train-driven atomic precipitation.

[0031] like Figure 1 As shown, the femtosecond laser micro-nano fabrication system includes a Ti:sapphire femtosecond laser 1, a mirror, an energy adjustment module, a beam shaping module 7, a laser processing module, and a real-time imaging module; The Ti:sapphire femtosecond laser 1 generates a femtosecond laser, which is reflected and propagated by the first mirror 2 and the second mirror 5. The energy adjustment module includes a half-wave plate 3 and a polarizer 4. The laser polarization direction is changed by rotating the half-wave plate 3, and then a fixed-direction polarization is generated by the polarizer 4 to achieve stepless energy adjustment. The beam shaping module 7 includes multiple birefringent crystals of different thicknesses, with the optical axes of adjacent crystals at 45°, generating pulse trains with fixed time intervals; The laser processing module includes a mechanical optical shutter 6, a galvanometer system 8, a scanning mirror 9, a collimating mirror 10, a dichroic mirror 11, a focusing mirror turntable 12, a focusing mirror 13, a sample fixture 15, and a three-dimensional displacement stage 16. The mechanical optical shutter 6 controls the switching of the laser by opening and closing, and works with the galvanometer system 8 and the three-dimensional displacement stage 16 to achieve processing with specified parameters. The laser is reflected from the surface of the dichroic mirror 11 and enters the focusing mirror 13 to process the surface of the sample 14. The sample 14 is fixed on the three-dimensional displacement stage 16 by the sample fixture 15 to achieve relative movement with the laser. The focusing mirror turntable 12 enables the switching of focusing mirrors 13 with different magnifications. The real-time imaging module includes a beam splitter 17, a halogen lamp 18, an imaging lens group 19, and an imaging camera 20. The halogen lamp 18 provides white light illumination, which illuminates the surface of the sample 14 after passing through the beam splitter 17, the dichroic mirror 11, and the focusing mirror 13. The reflected light passes through the dichroic mirror 11 and is reflected on the surface of the beam splitter 17 before entering the imaging lens group 19. After being focused, the light is collected in the imaging camera 20. The imaging lens group 19 moves the imaging surface by adjusting the lens spacing.

[0032] The thickness of the birefringent crystal in beam shaping module 7 is selected according to the required pulse train time interval and number of pulses, and the crystal thickness is halved one by one along the laser incident direction.

[0033] The parameters of the femtosecond laser pulse are: pulse width 100 fs, center wavelength 800 nm, and repetition frequency 1 kHz.

[0034] The imaging plane of the imaging camera 20 is adjusted to the same height as the laser focal plane by the imaging lens group 19.

[0035] Dichroic mirror 11 reflects near-infrared laser light with a center wavelength of 800 nm and transmits imaging white light with a center wavelength of 400 nm–730 nm.

[0036] The pulse overlap rate is achieved by adjusting the scanning speed of the galvanometer system 8.

[0037] The laser energy ranges from 1.5 mW to 50 mW.

[0038] In one embodiment of the present invention, femtosecond laser pulse trains drive atomic precipitation, and the specific steps are as follows: Step 1: Place the nickel-based superalloy sample in a glass container, which is fixed on the three-dimensional displacement stage 16 with sample clamp 15. Add alcohol solution to the glass container at a position 2 mm above the sample surface. Step 2: Rotate the focusing mirror turntable 12 to the empty position, open the mechanical optical shutter 6, and adjust the first reflecting mirror 2, the second reflecting mirror 5 and the dichroic mirror 11 to ensure that the laser is perpendicularly incident on the surface of the alloy sample 14 and passes through the center of the focusing mirror mounting hole at the same time. Step 3: Close the mechanical shutter 6, and rotate the focusing lens dial 12 to select the focusing lens 13 as a 150 mm focal length plano-convex lens; Step 4: Open the mechanical optical shutter 6, move the three-dimensional displacement stage 16 along the z-axis, and find the position of the smallest spot, which is the laser focusing plane; Step 5: Close the mechanical shutter 6, turn on the halogen lamp 18 and adjust its horizontal position to ensure that the processing area is illuminated. At the same time, adjust the imaging lens group 19 so that the imaging camera 20 can capture a clear image of the sample surface. Step 6: Add beam shaping module 7, select two birefringent crystals with thicknesses of 11.2 mm and 5.6 mm, with the 11.2 mm thick crystal in front; Step 7: Adjust the crystal angles by rotating the mirror frame. The optical axis of the 11.2 mm thick crystal forms a 45° angle with the original laser polarization direction, and the optical axis of the 5.6 mm thick crystal forms a 45° angle with the optical axis of the 11.2 mm thick crystal, generating a pulse train containing 4 pulses with a pulse interval of 4 ps. Figure 2 As shown; Step 8: Adjust half-wave plate 3 to determine the femtosecond laser power to be 7 mW; Step 9: Control the scanning speed of the galvanometer system 8 to 500 mm / s using the host computer software, scan a 300 μm square area, with a scan line interval of 5 μm, and perform processing in conjunction with the opening and closing of the mechanical optical shutter 6; Step 10: After processing, sonicate the alcohol solution for 10 minutes, then use a 20μL pipette tip to draw up 3 drops of the solution and place them on the copper mesh.

[0039] like Figure 3The image shows the morphology of the ejecta and the distribution of elements within it under a transmission electron microscope (TEM). The initially formed nanospheres are dominated by elements with high relative atomic masses, such as rhenium (Re, 186.207), tungsten (W, 183.84), tantalum (Ta, 180.9479), hafnium (Hf, 178.49), cobalt (Co, 58.9332), and nickel (Ni, 58.6934). Other elements, such as chromium (Cr, 51.9961), aluminum (Al, 26.9815), and carbon (C, 12.011), are uniformly distributed within the flocculent material. Molybdenum (Mo, 95.95) and niobium (Nb, 92.906) are present in very small amounts in nickel-based superalloys and are therefore not considered. In nickel-based superalloys, the contents of Co and Cr are roughly equal, but Co aggregates in the initially formed nanospheres, while Cr is uniformly distributed. This is because the femtosecond laser drives the relatively smaller Cr, resulting in more vigorous diffusion, while Co moves relatively slowly, thus combining to form nanoparticles. This result demonstrates that femtosecond lasers can achieve differential driving of elements with different relative atomic masses, thereby controlling the types of elements in the preparation of subtractive nanoparticles, which can be applied to energy fields such as chemical catalysis.

[0040] Beam shaping module 7 utilizes the different refractive indices of the two optical axes within the crystal, combined with the crystal thickness, to obtain different pulse delays. The calculation formula is as follows:

[0041] in, For pulse delay, and It has two optical axes, namely Light and Light, The speed of light in a vacuum. The thickness of the crystal; The formula for calculating the refractive index of two optical axes with respect to a specific wavelength of light is:

[0042]

[0043] in, The incident laser wavelength; By adjusting the angle between the optical axis of the birefringent crystal and the polarization of the incident laser, the energy ratio of the two pulses can be flexibly controlled. Based on the vector decomposition of linearly polarized light, the energy ratio along the optical axis can be obtained. Light and perpendicular to the optical axis The light amplitude is:

[0044]

[0045] in, and They are respectively Light and The amplitude of light The angle between the incident laser polarization and the crystal optical axis. The incident laser amplitude; According to the Fresnel amplitude formula, the ratio of the intensities of the two beams is:

[0046] in, and They are respectively Light and The intensity of light.

[0047] The extended calculation steps for the two-dimensional molecular dynamics coupled two-temperature equation model are as follows: Molecular dynamics models are used to analyze the lattice dynamics of materials, while two-temperature equations are used to capture the energy transfer process between the photon-electron-lattice system under femtosecond laser irradiation. Coupled calculations of these two methods enable atomic-level observation of ablation dynamics and provide detailed analysis of elemental segregation phenomena in the ejected materials. The main formulas are as follows:

[0048]

[0049]

[0050] in, C e Represents electron heat capacity, T e Represents electron temperature. k e Representing electronic thermal conductivity, the above parameters describe the temperature rise and heat transfer capabilities of an electronic system. G Representing the electro-acoustic coupling coefficient, it describes the rate of heat transfer from electrons to the lattice system; in molecular dynamics models, it is calculated using the equations of atomic motion, representing atoms. i The quality is m i The speed is v i The force acting on it is F i The energy transfer between electrons and the lattice system is represented by the friction term ( ) and the random force of the Langewan thermostat ( The lattice temperature can be calculated by statistically analyzing the atomic kinetic energies throughout the entire lattice system. T l ,in, To calculate the number of atoms in the group, is the Boltzmann constant.

[0051] laser source S The formula used to describe the absorption of photons by electrons is as follows:

[0052] Multi-pulse excitation involves superimposing laser source terms with different delays. Under pulse train ablation with a pulse interval of 4 ps and containing 4 sub-pulses, the atomic content of Al changes with height at time 230 ps as follows: Figure 4 As shown, since the relative atomic mass of Al is much lower than that of Ni, its atomic ratio gradually increases with increasing height, which confirms the phenomenon of elemental segregation from the perspective of numerical model.

[0053] The method in Example 2 is the same as in Example 1, except that the laser energy is adjusted to 50 mW; Processing results as follows Figure 5 As shown, spherical nanoparticles were generated, and there was a clear phenomenon of aggregation of high relative atomic mass elements and diffusion of low mass elements.

[0054] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of the invention.

Claims

1. A method of atomic emission driven by a train of femtosecond laser pulses, characterized in that, Realize based on femtosecond laser micro-nano machining system, It includes the following steps: S1: the alloy material is fixed on the three-dimensional displacement table; S2: the angle of the dichroic mirror is adjusted, so that the femtosecond laser pulse is vertically incident to the alloy material surface; S3: adjust the processing focusing mirror to ensure that the laser is coaxially vertically incident; S4: adjust the imaging camera to monitor the laser processing area in real time through the real-time imaging module; S5: adjust the beam shaping module to generate a pulse train with fixed pulse interval; S6: adjust the laser energy, and through the cooperation of the galvanometer system, three-dimensional displacement table and mechanical light shutter, different pulse overlap rates are processed on the specified area of the material surface, and the femtosecond laser pulse train driving atom precipitation is completed.

2. The method of claim 1, wherein the femtosecond laser pulse train is characterized by a pulse repetition rate of 1 MHz or greater. The femtosecond laser micro-nano machining system includes a titanium sapphire femtosecond laser (1), a mirror, an energy adjustment module, a beam shaping module (7), a laser processing module and a real-time imaging module; The titanium sapphire femtosecond laser (1) generates femtosecond laser, which is reflected and propagated by the first mirror (2) and the second mirror (5); The energy adjustment module includes a half-wave plate (3) and a polarizer (4), which changes the polarization direction of the laser by rotating the half-wave plate (3), and then generates a fixed direction polarization through the polarizer (4) to realize stepless energy adjustment; The beam shaping module (7) includes a plurality of birefringent crystals with different thicknesses, and the optical axes of adjacent crystals are at 45°, generating a pulse train with fixed time interval; The laser processing module includes a mechanical light shutter (6), a galvanometer system (8), a scanning mirror (9), a collimating mirror (10), a dichroic mirror (11), a focusing mirror turntable (12), a focusing mirror (13), a sample clamp (15) and a three-dimensional displacement table (16). The mechanical light shutter (6) controls the opening and closing of the laser, and cooperates with the galvanometer system (8) and the three-dimensional displacement table (16) to realize processing with specified parameters. The laser is reflected on the surface of the dichroic mirror (11) and enters the focusing mirror (13) to process the surface of the sample (14). The sample (14) is fixed on the three-dimensional displacement table (16) by the sample clamp (15) to realize relative movement with the laser. The focusing mirror turntable (12) realizes the switching of focusing mirrors (13) with different magnifications. The real-time imaging module includes a beam splitter (17), a halogen lamp (18), an imaging lens group (19) and an imaging camera (20). The halogen lamp (18) provides white light illumination, which illuminates the surface of the sample (14) after passing through the beam splitter (17), the dichroic mirror (11) and the focusing mirror (13). The reflected light is reflected on the surface of the beam splitter (17) after passing through the dichroic mirror (11) and enters the imaging lens group (19), which is focused in the imaging camera (20) after focusing. The imaging lens group (19) moves the imaging surface by adjusting the lens spacing.

3. The method of claim 2, wherein the femtosecond laser pulse train is characterized by a pulse repetition rate of 1 MHz or greater. The thickness of the birefringent crystal of the beam shaping module (7) is selected according to the required pulse train time interval and pulse number, and the thickness of the crystal decreases by half along the laser incident direction.

4. The method of claim 2, wherein the femtosecond laser pulse train is characterized by a pulse repetition rate of 1 MHz or greater. The parameters of the femtosecond laser pulse are: pulse width 100 fs, center wavelength 800 nm, repetition frequency 1 kHz.

5. The method of claim 2, wherein the femtosecond laser pulse train is characterized by a pulse repetition rate of 1 MHz or greater. The imaging plane of the imaging camera (20) is adjusted to the same height as the laser focal plane by the imaging lens group (19).

6. The method of claim 2, wherein the femtosecond laser pulse train is characterized by a pulse repetition rate of 1 MHz or greater. The biprism (11) reflects near-infrared laser with a center wavelength of 800 nm and transmits imaging white light with a center wavelength of 400 nm-730 nm.

7. The method of claim 2, wherein the femtosecond laser pulse train is characterized by a pulse repetition rate of 1 MHz or greater. The pulse overlap rate is achieved by adjusting the scanning speed of the galvanometer system (8).

8. The method of claim 2, wherein the femtosecond laser pulse train is characterized by a pulse repetition rate of 1 MHz or greater. The laser energy is 1.5 mW-50 mW.

9. The method of claim 2, wherein the femtosecond laser pulse train is characterized by a pulse repetition rate of 1 MHz or greater. The beam shaping module (7) utilizes the different refractive indexes of two optical axes in the crystal and combines the crystal thickness to obtain different pulse delays, and the calculation formula is: wherein is the pulse delay, and are the two optical axes, respectively light and light, is the speed of light in vacuum, is the crystal thickness; The refractive index calculation formula of two optical axes for specific wavelength light is: wherein for the incident laser wavelength; By adjusting the angle between the optical axis of birefringent crystal and the polarization of incident laser, the energy ratio of two pulses can be flexibly controlled. According to the vector decomposition of linearly polarized light, the amplitude of light along the optical axis direction and the light perpendicular to the optical axis are: ​​ wherein and are respectively light and amplitude of light, is the angle between the incident laser polarization and the crystal optical axis, is the incident laser amplitude; According to the Fresnel amplitude formula, the ratio of the intensities of the two beams is: wherein and are light and intensity of light.

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