A femtosecond laser machining system and method

Abstract

The application relates to the technical field of laser micro-nano processing, and particularly provides a femtosecond laser processing system and method, wherein the femtosecond laser processing system comprises a laser emission module and a beam shaping module; the beam shaping module comprises a pulse separator, a spatial light modulator and a beam expander; the laser emission module, the pulse separator, the beam expander and the spatial light modulator are sequentially arranged; the laser emission module is used for emitting laser pulses; the laser pulses sequentially pass through the pulse separator and the beam expander and then reach the spatial light modulator; the pulse separator is used for splitting the laser pulses and introducing a pulse delay time between the split laser pulses; the beam expander is used for expanding the laser beam; and the spatial light modulator is used for shaping a Gaussian beam into a flat-top beam. The application has the effect of improving the processing quality of nanochannels on a grating surface.

Description

Technical Field

[0001] This invention relates to the technical field of laser micro-nano fabrication, and more specifically, to a femtosecond laser fabrication system and method. Background Technology

[0002] High-power semiconductor lasers, as a crucial piece of national equipment, have long been limited in their development due to insufficient performance of frequency-selective gratings. The materials used in these gratings and the microgroove structure of their surface arrays directly determine their performance. Based on the high energy density and extremely short pulse width of femtosecond lasers, the generation of periodic micro / nano structures on material surfaces can be induced. This structure can overcome the limitations of spot size, producing more refined array microgroove structures.

[0003] However, the fabrication quality of microgroove structures is affected by various factors, such as laser power, pulse width control precision, and material surface condition. With the continuous development of semiconductor devices, the forming quality of periodic microgroove structures for gratings is particularly important. However, the structures currently fabricated are difficult to meet the requirements in terms of minimum linewidth, regularity, and aspect ratio. Summary of the Invention

[0004] To improve the processing quality of nanochannels on the grating surface, this invention provides a femtosecond laser processing system and method.

[0005] In a first aspect, the present invention provides a femtosecond laser processing system, including a laser emitting module and a beam shaping module, wherein the beam shaping module includes a pulse splitter, a spatial light modulator and a beam expander, and the laser emitting module, the pulse splitter, the beam expander and the spatial light modulator are arranged sequentially;

[0006] The laser emitting module is used to emit laser pulses. The laser pulses pass through the pulse splitter and the beam expander in sequence before reaching the spatial light modulator. The pulse splitter is used to split the laser pulses and introduce a pulse delay time between the split laser pulses. The beam expander is used to expand the laser beam. The spatial light modulator is used to shape the Gaussian beam into a flat-top beam.

[0007] Optionally, the beam shaping module further includes a half-wave plate, which is disposed between the laser emitting module and the pulse splitter. The laser pulse passes through the half-wave plate, the pulse splitter and the beam expander in sequence before reaching the spatial light modulator.

[0008] Optionally, the femtosecond laser processing system further includes a workpiece processing module;

[0009] The workpiece processing module includes a working container, a filter, and a vacuum pump. The working container has a receiving cavity for accommodating the workpiece.

[0010] The vacuum pump, the filter, and the receiving cavity are connected in sequence. The vacuum pump is used to extract the powder and gas generated in the receiving cavity during the workpiece processing, and the filter is used to filter the extracted powder.

[0011] Optionally, the working container includes a first split section and a second split section, which are detachably connected and form the receiving cavity.

[0012] Optionally, the working container further includes an optical glass plate, the first split portion has an opening, the opening communicates with the receiving cavity, the optical glass plate is disposed at the opening, and the optical glass plate is used to allow light to pass through the receiving cavity.

[0013] Optionally, the working container has an air inlet and an air outlet on two side walls perpendicular to the laser pulse incident direction, respectively. The air inlet and the air outlet are respectively connected to the receiving cavity, and the air pump, the filter and the air outlet are connected in sequence.

[0014] And / or, a sealing gasket is provided between the optical glass sheet and the first split portion.

[0015] Optionally, the workpiece processing module further includes a micro-nano stage, on which the working container is disposed, and the micro-nano stage is used to control the movement of the working container.

[0016] Optionally, the femtosecond laser processing system further includes a focusing observation module and an optical path adjustment module. The focusing observation module includes a white light source, an attenuator, a filter, and a CCD camera. The optical path adjustment module includes a visible light transmission laser mirror, a non-polarized white light beam splitter, and an objective lens.

[0017] The laser pulse passes sequentially through the spatial light modulator and the visible light transmission laser reflector before reaching the objective lens. The unpolarized white light beam splitter separates the white light emitted from the white light source into low-intensity reflected light and low-intensity refracted light. The low-intensity reflected light passes through the visible light transmission laser reflector before reaching the objective lens. The low-intensity refracted light passes sequentially through the attenuator and the filter before reaching the CCD camera. The CCD camera receives and processes the optical signal formed by the conversion of the low-intensity refracted light to observe the focusing of the laser pulse.

[0018] Secondly, the present invention also provides a femtosecond laser processing method, the femtosecond laser processing method being based on the above-mentioned femtosecond laser processing system, the femtosecond laser processing method comprising:

[0019] After placing the workpiece in the working container, turn on the vacuum pump and filter;

[0020] Turn on the laser emission module to output a femtosecond laser, so that the femtosecond laser is incident perpendicularly on the objective lens and focused on the workpiece surface, and then turn off the laser emission module;

[0021] After setting the output parameters of the laser emission module and the pulse delay time of the pulse splitter, reopen the laser emission module, optical path adjustment module, and beam shaping module to process the workpiece;

[0022] In the process of splicing and processing workpieces, the micro-nano stage is controlled to move the workpieces at intervals of half a cycle or odd multiples of half a cycle.

[0023] Optionally, the output parameters of the laser emission module include: a minimum pulse width of 255 fs, a fundamental wavelength of 1030 nm, and a corresponding maximum output power of 16 W; a second-harmonic laser wavelength of 515 nm and an output power of 6 W; a fourth-harmonic laser wavelength of 257 nm and an output power of 1 W; a laser frequency of 1 kHz to 1100 kHz; and a scanning speed adjustable from 0.1 mm / s to 80 mm / s.

[0024] The pulse splitter introduces a delay of ±14 ps between the split pulses. 。

[0025] The beneficial effects of this invention are:

[0026] In this embodiment of the invention, a pulse splitter, a beam expander, and a spatial light modulator are sequentially arranged after the laser emission module. This allows the femtosecond laser to first undergo pulse splitting to optimize the energy and parameters of the laser pulses, then the beam expander further improves the beam quality and characteristics, and finally the spatial light modulator shapes the beam. Pulse splitting followed by beam expansion ensures that each split pulse maintains consistent characteristics after beam expansion, resulting in a more uniform beam shape. The beam expander increases the laser beam diameter, reducing the energy density per unit area and preventing damage to the subsequent spatial light modulator due to excessively high local energy. Simultaneously, the collimated beam after beam expansion reduces the divergence angle, making the optical path more stable and providing a uniform incident field for the subsequent spatial light modulator. Compared to single-pulse or simple beam splitting, this invention, by adjusting the pulse delay time, can promote the ablation efficiency of materials. It also has significant advantages in improving the spatial regularity of the arrayed microgrooves on the material surface, reducing the roughness of the groove edges, and increasing the aspect ratio of the structure, effectively improving the processing quality of the arrayed nanogrooves. Spatial shaping of the light spot can improve processing efficiency, reduce processing size, and improve the verticality and depth of the microgrooves. The semi-cycle mismatch processing method can improve the regularity of the arrayed microgrooves. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall structure of the femtosecond laser processing system in an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the femtosecond laser processing system in an embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of the structure of the working container in an embodiment of the present invention;

[0030] Figure 4 This is a schematic diagram of the femtosecond laser processing route in an embodiment of the present invention;

[0031] Figure 5 Here is a scanning electron microscope image of the workpiece after laser processing in an embodiment of the present invention;

[0032] Figure 6 This is a transmission electron microscope (TEM) image of the cross-section of the workpiece after laser processing in an embodiment of the present invention;

[0033] Explanation of reference numerals in the attached figures:

[0034] 1. Laser emitting module; 21. Half-wave plate; 22. Pulse splitter; 23. Beam expander; 24. Spatial light modulator; 31. Shutter; 32. Optical path adjustment mirror; 33. Visible light transmission laser mirror; 34. Unpolarized white light beam splitter; 35. Objective lens; 41. White light source; 42. Attenuator; 43. Filter; 44. CCD camera; 45. Optical lens; 51. Working container; 511. Receiving cavity; 512. Air inlet; 513. Air outlet; 514. First splitting section; 515. Second splitting section; 516. Sealing gasket; 517. Optical glass plate; 52. Filter; 53. Vacuum pump; 54. Micro / nano stage; 6. Power module; 7. Nanochannel. Detailed Implementation

[0035] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0036] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the description of this application is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0037] The term "comprising" and its variations as used herein are open-ended, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the description below. It should be noted that the concepts of "first," "second," etc., mentioned in this invention are used to distinguish different objects, not to describe a specific order or hierarchy. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0038] Figure 1 This is a schematic diagram of a femtosecond laser processing system according to an embodiment of the present invention. (Refer to...) Figure 1 As shown, the femtosecond laser processing system includes a laser emission module 1 and a beam shaping module. The beam shaping module includes a pulse splitter 22, a beam expander 23, and a spatial light modulator 24. The laser emission module 1, pulse splitter 22, beam expander 23, and spatial light modulator 24 are arranged sequentially. The laser emission module 1 emits laser pulses. The laser pulses pass through the pulse splitter and beam expander sequentially before reaching the spatial light modulator. The pulse splitter 22 splits the laser pulses and introduces a pulse delay time between the split laser pulses. The beam expander 23 expands the laser beam, and the spatial light modulator 24 shapes the Gaussian beam into a flat-top beam.

[0039] It should be noted that the femtosecond laser processing system of the present invention can be used to process nanoscale grooves or recesses, i.e., nanochannels 7, on the surface of gratings, specifically for processing workpieces represented by gallium arsenide materials. The laser emission module 1 in this embodiment is specifically a femtosecond laser. The pulse width of a femtosecond laser is extremely short, and photon energy is concentrated within the extremely short pulse, resulting in extremely high instantaneous power. Due to the extremely short pulse, the thermal impact during femtosecond laser processing is relatively small, reducing thermal impact and defects such as microcracks around the workpiece processing area. The pulse splitter 22 is a device for pulse splitting and recombination, which can split one pulse into two sub-pulses, two sub-pulses into four sub-pulses, and so on. Simultaneously, a controllable pulse delay time is introduced between the split laser pulses, thereby distributing the energy of the laser pulse over time, making the energy of each pulse more concentrated, improving the efficiency of laser-material interaction, and better inducing periodic surface structures. Furthermore, since spatial light modulators generally have requirements for the incident light, typically requiring the incident beam diameter to reach a certain value—usually larger than the diameter of the beam directly emitted by the laser—the beam expander 23 can effectively reduce the beam divergence angle and increase the beam diameter, making the beam more parallel. Simultaneously, it can reduce the laser's energy density, preventing damage to the spatial light modulator 24. The spatial light modulator 24 is used to modulate the spatial distribution of the laser wave, shaping the Gaussian beam emitted by the femtosecond laser into a flat-top beam that is easier to process into regular nanochannels 7. In laser processing, the energy distribution of a Gaussian beam is uneven, with high energy at the center and low energy at the edges. This leads to inconsistent energy density in the processing area, affecting processing accuracy. A flat-top beam, on the other hand, has a uniform energy distribution, providing a consistent energy density throughout the processing area, thereby improving processing accuracy.

[0040] In this embodiment of the invention, a pulse splitter 22, a beam expander 23, and a spatial light modulator 24 are sequentially arranged after the laser emission module 1. This allows the femtosecond laser to first undergo pulse splitting to optimize the energy and parameters of the laser pulses, then the beam expander 23 further improves the beam quality and characteristics, and finally the spatial light modulator 24 shapes the beam. Pulse splitting followed by beam expansion ensures that each split pulse maintains consistent characteristics after beam expansion, resulting in a more uniform beam spot. The beam expander 23 increases the laser beam diameter, reducing the energy density per unit area and preventing damage to the subsequent spatial light modulator 24 due to excessively high local energy. Simultaneously, the collimated beam after beam expansion reduces the divergence angle, making the optical path more stable and providing a uniform incident field for the subsequent spatial light modulator 24. Compared to single-pulse or simple beam splitting, this invention, by adjusting the pulse delay time, can promote the ablation efficiency of materials. It also has significant advantages in improving the spatial regularity of the arrayed microgrooves on the material surface, reducing the roughness of the groove edges, and increasing the aspect ratio of the structure, effectively improving the processing quality of the arrayed nanogrooves. Spatial reshaping of the light spot can improve processing efficiency, reduce processing size, and improve the verticality and depth of the microgroove.

[0041] In some alternative embodiments, refer to Figure 1 and Figure 2 As shown, the beam shaping module also includes a half-wave plate 21, which is disposed between the laser emitting module 1 and the pulse splitter 22. The laser pulse passes sequentially through the half-wave plate, the pulse splitter, and the beam expander before reaching the spatial light modulator. The half-wave plate 21 can change the polarization direction of the incident light. By rotating the half-wave plate 21, the polarization state of the incident light (i.e., the laser pulse emitted by the laser emitting module 1) can be adjusted to match the polarization characteristics of the pulse splitter 22, thereby improving the separation efficiency and accuracy of the pulse splitter 22.

[0042] In some alternative embodiments, refer to Figure 1 and Figure 2 As shown, the femtosecond laser processing system also includes an optical path adjustment module, which includes a shutter 31 positioned between the laser emission module 1 and the half-wave plate 21. The shutter 31 is installed after the laser emission module 1 and is used to allow or block laser pulses.

[0043] Furthermore, referring to Figure 1 and Figure 2 As shown, the optical path adjustment module also includes multiple optical path adjustment mirrors 32 for adjusting the direction of the optical path. Specifically, there are three optical path adjustment mirrors 32, which are distributed between the half-wave plate 21 and the pulse splitter 22, between the pulse splitter 22 and the beam expander 23, and between the beam expander 23 and the spatial light modulator 24.

[0044] In some alternative embodiments, refer to Figure 1 and Figure 2 As shown, the femtosecond laser processing system also includes a focusing observation module, which comprises a white light source 41, an attenuator 42, a filter 43, a CCD camera 44, and an optical lens 45. The optical path adjustment module further includes a visible light transmission laser mirror 33, a non-polarized white light beam splitter 34, and an objective lens 35. The spatial light modulator 24, the visible light transmission laser mirror 33, and the objective lens 35 are arranged sequentially. The non-polarized white light beam splitter 34 is positioned on one side of the visible light transmission laser mirror 33. The white light source 41, the non-polarized white light beam splitter 34, the attenuator 42, the filter 43, the CCD camera 44, and the optical lens 45 are arranged sequentially. The laser pulse passes sequentially through the spatial light modulator 24 and the visible light transmission laser mirror 33 before reaching the objective lens 35. The unpolarized white light beam splitter 34 separates the white light emitted from the white light source 41 into low-intensity reflected light and low-intensity refracted light. The low-intensity reflected light passes through the visible light transmission laser reflector 33 to reach the objective lens 35, while the low-intensity refracted light passes through the attenuator 42 and the filter 43 before reaching the CCD camera 44. The attenuator 42 and the filter 43 convert the low-intensity refracted light output from the unpolarized white light beam splitter 34 into a signal that the CCD camera 44 can receive and process. The CCD camera 44 receives and processes the optical signal formed by the conversion of the low-intensity refracted light and observes whether the laser pulse is focused on the workpiece surface through the optical lens 45 to observe the surface condition of the workpiece.

[0045] Specifically, refer to Figure 1 and Figure 2 As shown, the laser emitted from the spatial light modulator 24 is reflected by the visible light transmission laser mirror 33 to the objective lens 35 and finally focused onto the workpiece surface. Simultaneously, the white light source 41 emits white light, which is separated into low-intensity reflected light and low-intensity refracted light by the non-polarized white light beam splitter 34. The low-intensity reflected light is transmitted through the visible light transmission laser mirror 33 to the objective lens 35 and also focused onto the workpiece surface; while the low-intensity refracted light is processed sequentially by the attenuator 42 and the filter 43 before entering the CCD camera 44, allowing observation of the workpiece surface through the optical lens 45. This facilitates finding the processing position and focal point with high precision, and also allows for a certain degree of observation of the processed sample.

[0046] This invention utilizes a non-polarized white light beam splitter 34 to separate low-intensity reflected and refracted light, avoiding interference from high-energy lasers on the CCD camera 44 and optical lens 45, thus enabling simultaneous processing and observation. Compared to existing technologies that require switching optical paths or pausing processing to adjust the focus, this invention ensures the stability of real-time monitoring through its beam-splitting design.

[0047] In some alternative embodiments, refer to Figure 1 and Figure 2 As shown, the femtosecond laser processing system also includes a workpiece processing module, which is located on the side of the objective lens 35 away from the visible light transmission laser mirror 33. The workpiece processing module includes a working container 51, a filter 52, and a vacuum pump 53. The working container 51 has a receiving cavity 511 for accommodating the workpiece. The vacuum pump 53, filter 52, and receiving cavity 511 are connected in sequence. The vacuum pump 53 is used to extract the powder and gas generated in the receiving cavity 511 during workpiece processing, and the filter 52 is used to filter the extracted powder.

[0048] Specifically, the laser emitted by the laser emitting module 1 undergoes pulse separation and beam shaping sequentially, and then the laser beam is focused onto the workpiece surface inside the working container 51 by the objective lens 35. The working container 51 can be square, and the vacuum pump 53 and filter 52 can be connected sequentially to the air outlet 513 of the working container 51. The vacuum pump 53 can remove toxic powder and gas generated during the processing inside the working container 51, and the filter 52 can effectively filter the toxic powder extracted from the working container 51, with a filtration accuracy of 0.2 μm.

[0049] When processing workpieces made of specific materials (such as gallium arsenide) using the femtosecond laser processing system of this invention, the powder generated during processing, being a toxic substance, can easily affect the physical and mental health of operators. This invention addresses this by employing a vacuum pump 53 and a filter 52 to simultaneously remove toxins during the processing, ensuring both processing safety and surface quality.

[0050] In some alternative embodiments, refer to Figure 3 As shown, the working container 51 of this embodiment includes a first split portion 514 and a second split portion 515, which are detachably connected and form a receiving cavity 511. In an exemplary embodiment, referring to... Figure 3 As shown, the first splitting part 514 and the second splitting part 515 can be cuboid blocks of equal size. Each cuboid block has a groove of the same area inside. The first splitting part 514 and the second splitting part 515 can be placed together vertically to align and connect the two grooves, thereby forming a receiving cavity 511. The two parts can be fixed together using bolts or other fasteners at their four corners. By adopting a split design for the working container 51, it is beneficial for placing the workpiece while allowing the workpiece processing to be carried out within the relatively sealed receiving cavity 511, avoiding the influence of external environmental factors on the processing, thereby improving the processing quality of the nanochannels 7.

[0051] In some alternative embodiments, refer to Figure 3As shown, the working container 51 also includes an optical glass plate 517. The first split part 514 has an opening that communicates with the receiving cavity 511. The optical glass plate 517 is disposed at the opening and is used to allow light to pass through the receiving cavity 511.

[0052] Specifically, the opening can be located in the middle region of the upper surface of the first split section 514, which serves as the laser irradiation area during processing. The thickness of the optical glass plate 517 can be specifically 500um to 600um, possessing excellent light transmittance properties for ultraviolet, green, and infrared light. The light transmittance properties of the optical glass plate 517 facilitate real-time observation of the workpiece's processing status by the operator.

[0053] Furthermore, in some optional embodiments, reference is made to... Figure 3 As shown, the working container 51 has an air inlet 512 and an air outlet 513 on its side wall perpendicular to the laser pulse incident direction. The air inlet 512 and the air outlet 513 are respectively connected to the receiving cavity 511. During suction filtration, air enters from the air inlet 512 of the working container 51 and exits from the air outlet 513, making the flow direction of the toxic powder controllable and avoiding interference with the laser processing. The end of the suction pump 53 away from the filter 52 is connected to an air pipe and inserted into water to achieve a double filtration effect.

[0054] In addition, to ensure the sealing performance between the optical glass plate 517 and the first split portion 514, refer to Figure 3 As shown, a sealing gasket 516 is provided between the optical glass plate 517 and the first split portion 514. The sealing gasket 516 can be attached between the edge of the optical glass plate 517 and the first split portion 514, and can be made of rubber. The sealing gasket 516 helps to ensure the sealing of the joint between the first split portion 514 and the second split portion 515, so that air can only enter the receiving cavity 511 through the air inlet 512 and be discharged through the air outlet 513.

[0055] In some alternative embodiments, refer to Figure 1 As shown, the workpiece processing module also includes a micro-nano stage 54, on which a work container 51 is disposed. The micro-nano stage 54 is used to control the movement of the work container 51. Specifically, Figure 4 This is a schematic diagram of the processing route in one embodiment of the present invention. The arrows in the diagram represent the moving direction of the micro-nano stage 54 when processing each row of nanochannels 7. Figure 5 and Figure 6 The images shown are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the workpiece after laser processing. It should be understood that during actual processing, the micro / nano stage 54 can control the working container 51 to move along the processing path to complete the processing of the nanochannel array on the workpiece surface.

[0056] In some alternative embodiments, refer to Figure 1 and Figure 2 As shown, the femtosecond laser processing system of the present invention also includes a power supply module 6. The laser emission module 1, shutter 31, pulse splitter 22, white light source 41, micro-nano stage 54, air pump 53 and CCD camera 44 are respectively connected to the power supply module 6, and the power supply module 6 supplies power to the above structures.

[0057] Secondly, the present invention also provides a femtosecond laser processing method for processing nanochannels 7, the femtosecond laser processing method being based on the aforementioned femtosecond laser processing system. The femtosecond laser processing method includes the following steps:

[0058] S1: First, turn on the power module 6, shutter 31, white light source 41 and CCD camera 44 in the focusing observation module. After placing the workpiece in the receiving cavity 511 in the working container 51, after installing the first split part 514 and the second split part 515, turn on the air pump 53 and filter 52. Connect the end of the air pump 53 away from the filter 52 to the air pipe and insert it into the water.

[0059] S2: Turn on the laser emission module 1 and shutter 31 to output a low-power femtosecond laser. At the same time, adjust the position of the beam expander 23 and each mirror so that the femtosecond laser spot is at the center of the beam expander 23 and each mirror group. With the help of the focusing observation module, the femtosecond laser is perpendicularly incident on the objective lens 35 and focused on the workpiece surface. Then turn off the laser emission module 1 and shutter 31.

[0060] This invention first pre-focuses with energy slightly higher than the ablation threshold to ensure the spot focal position is accurate before switching to the required parameters for processing. This avoids the risk of workpiece damage caused by inaccurate focus and improves the yield.

[0061] S3: After setting the output parameters of the laser emitting module 1 and the pulse delay time of the pulse separator 22, reopen the laser emitting module 1, the optical path adjustment module, and the beam shaping module. Rotate the half-wave plate 21 to adjust the polarization state of the femtosecond laser and process the workpiece. During the splicing process of the workpiece, control the micro-nano stage 54 to move the workpiece at intervals of half a cycle or odd multiples of half a cycle.

[0062] It should be noted that splicing processing specifically refers to the process in which, due to the limitation of the laser scanning range, different areas need to be scanned multiple times during large-area processing, and then these different scanned areas are spliced ​​together to form a larger area of ​​nanochannel array. This invention uses a continuous processing method to achieve the splicing of different scanned areas. In one specific embodiment, Figure 4In this design, each row of nanochannels 7 constitutes a scanning area. Since the formation and arrangement of the nanochannels 7 are achieved through workpiece movement during laser processing, this invention controls the micro / nano stage 54 to move the workpiece at intervals of half a cycle or odd multiples of half a cycle during splicing processing. That is, the interval between two adjacent scanning areas along the processing direction is half a cycle or an odd multiple of half a cycle, such as half a cycle, three-half a cycle, etc. The sum of the width of each nanochannel 7 and the distance between two adjacent nanochannels 7 in each scanning area constitutes the movement distance of one cycle. Figure 4 As shown, T / 2 refers to the distance traveled in half a cycle, and T refers to the distance traveled in one cycle.

[0063] This invention employs staggered processing to stitch together different scanning regions, which helps avoid the half-cycle mismatch phenomenon during the processing of nanochannels 7 and reduces bending misalignment between different rows of nanochannels 7. It should be noted that the half-cycle mismatch phenomenon refers to the situation during femtosecond laser processing, where residual heat from adjacent pulses at high repetition frequencies still creates a temperature gradient on the material surface. When the processing area moves to an adjacent position, the thermal expansion of the previously processed area changes the dielectric constant of the local material, leading to a change in the propagation speed of surface plasmon polariton waves (SPP), thereby disrupting the interference conditions between the laser and SPP and causing a periodic phase shift. Alternatively, the non-uniform stress generated after the processing material is heated can induce microscopic deformation, causing compression or stretching of the formed nanochannels 7 at the edges. If directly and continuously stitched, the periodic phases of the old and new areas cannot be aligned, resulting in a half-cycle mismatch at the stitching point. (Refer to...) Figure 5 and Figure 6 As shown, the present invention suppresses the thermal effect during processing by using a half-cycle or odd-multiple misaligned splicing method, optimizes the splicing offset, improves the consistency of the nanochannel array, and solves the problem of half-cycle mismatch during processing.

[0064] Further, in step S3, the output parameters of the laser emission module 1 include: a minimum pulse width of 255 fs, a fundamental wavelength of 1030 nm, and a corresponding maximum output power of 16 W; a second-harmonic laser wavelength of 515 nm and an output power of 6 W; a fourth-harmonic laser wavelength of 257 nm and an output power of 1 W; a laser frequency of 1 kHz to 1100 kHz; and a scanning speed adjustable from 0.1 mm / s to 80 mm / s. The pulse splitter 22 introduces a delay time of ±14 ps between the split pulses. Preferably, the fundamental wavelength is selected as 1030 nm, the output power as 160 mW, the laser frequency as 1 MHz, the scanning interval as 1.2 μm, the scanning speed as 10 mm / s, and the delay time of the pulse splitter is set to 8 ps. Using the above-mentioned laser output parameters and the delay time parameters introduced during pulse splitting as examples, the processing of gallium arsenide material effectively improves the minimum linewidth, regularity, and aspect ratio of the prepared nanochannel array.

[0065] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A femtosecond laser processing method, characterized in that, The femtosecond laser processing method is based on a femtosecond laser processing system, which includes a laser emitting module (1) and a beam shaping module. The beam shaping module includes a pulse splitter (22), a spatial light modulator (24), and a beam expander (23). The laser emitting module (1), the pulse splitter (22), the beam expander (23), and the spatial light modulator (24) are arranged sequentially. The laser emitting module (1) is used to emit laser pulses. The laser pulses pass through the pulse splitter (22) and the beam expander (23) in sequence before reaching the spatial light modulator (24). The pulse splitter (22) is used to split the laser pulses and introduce a pulse delay time between the split laser pulses. The beam expander (23) is used to expand the laser beam. The spatial light modulator (24) is used to shape the Gaussian beam into a flat-top beam. The femtosecond laser processing system also includes a workpiece processing module; the workpiece processing module includes a working container (51), a filter (52), a vacuum pump (53), and a micro-nano stage (54). The working container (51) is provided with a receiving cavity (511) for accommodating the workpiece; the vacuum pump (53), the filter (52), and the receiving cavity (511) are connected in sequence. The vacuum pump (53) is used to extract the powder and gas generated in the receiving cavity (511) during the workpiece processing, and the filter (52) is used to filter the extracted powder; the working container (51) is disposed on the micro-nano stage (54), and the micro-nano stage (54) is used to control the working container (51) to move along the processing path to complete the processing of the nano-groove array on the workpiece surface; The femtosecond laser processing system also includes an optical path adjustment module, which includes a visible light transmission laser mirror (33) and an objective lens (35). The laser pulse passes through the spatial light modulator (24) and the visible light transmission laser mirror (33) in sequence before reaching the objective lens (35). The femtosecond laser processing method includes: After placing the workpiece in the working container (51), turn on the vacuum pump (53) and the filter (52); Turn on the laser emission module (1) to output a femtosecond laser, so that the femtosecond laser is perpendicularly incident on the objective lens (35) and focused on the workpiece surface, and then turn off the laser emission module (1); After setting the output parameters of the laser emitting module (1) and the pulse delay time of the pulse separator (22), the laser emitting module (1), the optical path adjustment module and the beam shaping module are turned on again to process the workpiece. When splicing the workpiece, the micro-nano stage (54) is controlled to move the workpiece at intervals of half a cycle or an odd multiple of half a cycle. In the nanochannel array, each row of nanochannels (7) is a scanning area. The interval between two adjacent scanning areas along the processing direction is half a cycle or an odd multiple of half a cycle. The sum of the width of each nanochannel (7) and the distance between two adjacent nanochannels (7) in each scanning area is the moving distance of one cycle.

2. The femtosecond laser processing method according to claim 1, characterized in that, The beam shaping module also includes a half-wave plate (21), which is disposed between the laser emitting module (1) and the pulse splitter (22). The laser pulse passes through the half-wave plate (21), the pulse splitter (22) and the beam expander (23) in sequence before reaching the spatial light modulator (24).

3. The femtosecond laser processing method according to claim 1, characterized in that, The working container (51) includes a first split section (514) and a second split section (515), which are detachably connected and form the receiving cavity (511).

4. The femtosecond laser processing method according to claim 3, characterized in that, The working container (51) also includes an optical glass plate (517). The first split part (514) has an opening that communicates with the receiving cavity (511). The optical glass plate (517) is disposed at the opening and is used to allow light to pass through the receiving cavity (511).

5. The femtosecond laser processing method according to claim 4, characterized in that, The working container (51) has an air inlet (512) and an air outlet (513) on two side walls perpendicular to the laser pulse incident direction, respectively. The air inlet (512) and the air outlet (513) are respectively connected to the receiving cavity (511). The air pump (53), the filter (52) and the air outlet (513) are connected in sequence. And / or, a sealing gasket (516) is provided between the optical glass plate (517) and the first split portion (514).

6. The femtosecond laser processing method according to claim 1, characterized in that, The femtosecond laser processing system also includes a focusing observation module, which includes a white light source (41), an attenuator (42), a filter (43) and a CCD camera (44). The optical path adjustment module also includes a non-polarized white light beam splitter (34). The non-polarized white light beam splitter (34) is used to separate the white light emitted by the white light source (41) into low-intensity reflected light and low-intensity refracted light. The low-intensity reflected light passes through the visible light transmission laser reflector (33) to reach the objective lens (35). The low-intensity refracted light passes through the attenuator (42) and the filter (43) in sequence to reach the CCD camera (44). The CCD camera (44) is used to receive and process the optical signal formed by the conversion of the low-intensity refracted light to observe the focusing of the laser pulse.

7. The femtosecond laser processing method according to claim 1, characterized in that, The output parameters of the laser emitting module (1) include: a minimum pulse width of 255fs, a fundamental wavelength of 1030nm, and a corresponding maximum output power of 16W; a second-harmonic laser wavelength of 515nm and an output power of 6W; a fourth-harmonic laser wavelength of 257nm and an output power of 1W; a laser frequency of 1KHz to 1100KHz; and a scanning speed adjustable from 0.1mm / s to 80mm / s. The pulse splitter (22) introduces a delay time of ±14ps between the split pulses.

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