Femtosecond laser processing system and method

Abstract

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

Description

Technical Field

[0001] The present invention relates to the technical field of laser micro-nano processing, and in particular to a femtosecond laser processing system and method. Background Art

[0002] As a major national equipment, the development of high-power semiconductor lasers has been limited by the insufficient performance of frequency-selective gratings. The materials used for frequency-selective 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 the surface of materials can be induced. This structure can break through the limitation of spot size and produce a more sophisticated array microgroove structure.

[0003] However, the processing quality of microgroove structures is affected by many factors, such as laser power, pulse width control accuracy and material surface state. With the continuous development of semiconductor devices, the forming quality of the periodic microgroove structure of the grating is particularly important. However, the structures currently prepared are difficult to meet the requirements in terms of minimum line width, regularity, aspect ratio, etc. Summary of the invention

[0004] In order to improve the processing quality of nano-grooves on the surface of a grating, the present invention provides a femtosecond laser processing system and method.

[0005] In a first aspect, the present invention provides a femtosecond laser processing system, comprising a laser emission module and a beam shaping module, wherein the beam shaping module comprises a pulse separator, a spatial light modulator and a beam expander, wherein the laser emission module, the pulse separator, the beam expander and the spatial light modulator are arranged in sequence;

[0006] The laser emission module is used to emit laser pulses, and the laser pulses pass through the pulse separator and the beam expander in sequence before reaching the spatial light modulator. The pulse separator 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, and 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 separator, and the laser pulse sequentially passes through the half-wave plate, the pulse separator and the beam expander before reaching the spatial light modulator.

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

[0009] The workpiece processing module comprises a working container, a filter and an air pump, wherein a receiving cavity for receiving the workpiece is provided in the working container;

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

[0011] Optionally, the working container includes a first split portion and a second split portion, and the first split portion and the second split portion are detachably connected to form the accommodating cavity.

[0012] Optionally, the working container further comprises an optical glass sheet, the first split portion is provided with an opening, the opening is communicated with the accommodating cavity, the optical glass sheet is arranged at the opening, and the optical glass sheet is used to make the accommodating cavity transparent.

[0013] Optionally, an air inlet and an air outlet are respectively provided on two side walls of the working container perpendicular to the incident direction of the laser pulse, the air inlet and the air outlet are respectively connected to the accommodating 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 splitting part.

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

[0016] Optionally, the femtosecond laser processing system further comprises a focusing observation module and an optical path adjustment module, wherein the focusing observation module comprises a white light source, an attenuation plate, an optical filter and a CCD camera, and the optical path adjustment module comprises a visible light transmission laser reflector, a non-polarized white light beam splitter and an objective lens;

[0017] The laser pulse passes through the spatial light modulator and the visible light transmission laser reflector in sequence before reaching the objective lens. The non-polarized white light beam splitter is used to separate the white light emitted by 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 through the attenuation plate and the filter in sequence before reaching the CCD camera. The CCD camera is used to receive and process the optical signal formed by the transformation of the low-intensity refracted light so as to observe the focusing condition of the laser pulse.

[0018] In a second aspect, the present invention further provides a femtosecond laser processing method, which is based on the above-mentioned femtosecond laser processing system and comprises:

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

[0020] Turn on the laser emission module, output the femtosecond laser, make the femtosecond laser vertically incident 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 separator, the laser emission module, the optical path adjustment module and the beam shaping module are turned on again to process the workpiece;

[0022] When the workpiece is spliced, the micro-nano worktable is controlled to move the workpiece at intervals of half a period or an odd multiple of a half period.

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

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

[0025] The beneficial effects of the present invention are:

[0026] In an embodiment of the present invention, a pulse separator, a beam expander and a spatial light modulator are sequentially arranged after the laser emission module, so that the femtosecond laser first optimizes the energy and parameters of the laser pulse through pulse separation, and then further improves the quality and characteristics of the light beam through the beam expander, and finally performs shaping through the spatial light modulator. Beam expansion after pulse separation can ensure that each split pulse maintains consistent characteristics after beam expansion, so that the shaped light spot is more uniform. The beam expander expands the diameter of the laser beam, reduces the energy density per unit area, and avoids damage to the subsequent spatial light modulator due to excessive local energy. At the same time, the collimated beam after beam expansion can reduce the divergence angle, make the optical path more stable, and provide a uniform incident field for the subsequent spatial light modulator. Compared with a single pulse or simple splitting, the present invention can promote the ablation efficiency of the material by adjusting the pulse delay time. At the same time, it has great advantages in improving the spatial regularity of the array microgrooves on the surface of the material, reducing the roughness of the groove edge, and increasing the depth-to-width ratio of the structure, and can effectively improve the processing quality of the array nanogrooves. Spatial shaping of the light spot can improve processing efficiency, reduce processing scale, and increase verticality and depth of microgrooves. The semi-periodic mismatch processing method can improve the regularity of array microgrooves. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

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

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

[0033] Description of reference numerals:

[0034] 1. Laser emission module; 21. Half-wave plate; 22. Pulse separator; 23. Beam expander; 24. Spatial light modulator; 31. Shutter; 32. Optical path adjustment mirror; 33. Visible light transmission laser mirror; 34. Non-polarized white light beam splitter; 35. Objective lens; 41. White light source; 42. Attenuation plate; 43. Filter; 44. CCD camera; 45. Optical lens; 51. Working container; 511. Accommodating cavity; 512. Air inlet; 513. Air outlet; 514. First split part; 515. Second split part; 516. Sealing gasket; 517. Optical glass sheet; 52. Filter; 53. Vacuum pump; 54. Micro-nano workbench; 6. Power module; 7. Nanochannel. DETAILED DESCRIPTION

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be interpreted as being limited to the embodiments described herein. On the contrary, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes 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 meanings as those commonly understood by those skilled in the art to which this application belongs; the terms used in the specification of this application are only for the purpose of describing specific implementation methods and are not intended to limit this application;

[0037] The term "including" and its variations used in this article are open inclusions, that is, "including but not limited to"; the term "based on" is "based at least in part on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "optional embodiments". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts of "first" and "second" mentioned in the present invention are used to distinguish different objects, rather than to describe a specific order or a primary and secondary relationship. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, the meaning of "multiple" is two or more.

[0038] Figure 1 FIG. 1 is a schematic diagram of a femtosecond laser processing system according to an embodiment of the present invention. Figure 1 As shown, the femtosecond laser processing system includes a laser emitting module 1 and a beam shaping module, the beam shaping module includes a pulse separator 22, a beam expander 23 and a spatial light modulator 24, and the laser emitting module 1, the pulse separator 22, the beam expander 23 and the spatial light modulator 24 are arranged in sequence. The laser emitting module 1 is used to emit laser pulses, and the laser pulses sequentially pass through the pulse separator and the beam expander before reaching the spatial light modulator. The pulse separator 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, and the spatial light modulator 24 is used to shape 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 groove structures on the surface of the grating, that is, nano-grooves 7, and can specifically process workpieces represented by gallium arsenide materials. The laser emitting module 1 in the embodiment of the present invention is specifically a femtosecond laser. The pulse width of the femtosecond laser is extremely short, and the photon energy is concentrated in the extremely short pulse, resulting in extremely high instantaneous power. Due to the extremely short pulse, the thermal impact during the femtosecond laser processing is relatively small, which can reduce defects such as thermal impact and microcracks around the workpiece processing area. The pulse separator 22 is a device for pulse splitting and recombination, which can separate a pulse into two sub-pulses, two sub-pulses into four sub-pulses, and so on. At the same time, a controllable pulse delay time is introduced between the split laser pulses, so that the energy of the laser pulse can be distributed in time, so that the energy of each pulse is more concentrated, the efficiency of the interaction between the laser and the material is improved, and the periodic surface structure is better induced. In addition, since the spatial light modulator generally has requirements for the incident light, the incident light spot diameter is generally required to reach a certain value, which is generally larger than the spot diameter directly emitted by the laser. The beam expander 23 can effectively reduce the divergence angle of the light beam and increase the beam diameter, making the light beam more parallel, while reducing the energy density of the laser to avoid damage to the spatial light modulator 24. The spatial light modulator 24 is used to modulate the spatial distribution of the laser light wave, and can shape the Gaussian beam emitted by the femtosecond laser into a flat-top beam that is easier to process into regular nano-grooves 7. In laser processing, the energy distribution of the Gaussian beam is uneven, with high energy at the center and low energy at the edge, which will lead to inconsistent energy density in the processing area, thereby affecting the processing accuracy. The energy distribution of the flat-top beam is uniform, which can provide consistent energy density in the entire processing area, thereby improving the processing accuracy.

[0040] In the embodiment of the present invention, a pulse separator 22, a beam expander 23 and a spatial light modulator 24 are sequentially arranged after the laser emission module 1, so that the femtosecond laser is firstly separated by pulses to optimize the energy and parameters of the laser pulses, and then the beam expander 23 is used to further improve the quality and characteristics of the beam, and finally the spatial light modulator 24 is used to perform shaping. Beam expansion after pulse separation can ensure that each split pulse maintains consistent characteristics after beam expansion, so that the shaped light spot is more uniform. The beam expander 23 expands the diameter of the laser beam, reduces the energy density per unit area, and avoids the subsequent spatial light modulator 24 from being damaged due to excessive local energy. At the same time, the collimated beam after beam expansion can reduce the divergence angle, make the optical path more stable, and provide a uniform incident field for the subsequent spatial light modulator 24. Compared with a single pulse or simple splitting, the present invention can promote the ablation efficiency of the material by adjusting the pulse delay time, and at the same time has great advantages in improving the spatial regularity of the array microgrooves on the surface of the material, reducing the roughness of the groove edge, and increasing the depth-to-width ratio of the structure, and can effectively improve the processing quality of the array nanogrooves. Spatial shaping of the light spot can improve processing efficiency, reduce processing scale, and increase verticality and depth of micro-grooves.

[0041] In some optional embodiments, referring to Figure 1 and Figure 2 As shown, the beam shaping module also includes a half-wave plate 21, which is arranged between the laser emitting module 1 and the pulse separator 22. The laser pulse passes through the half-wave plate, the pulse separator and the beam expander in sequence 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 a direction that matches the polarization characteristics of the pulse separator 22, thereby improving the separation efficiency and accuracy of the pulse separator 22.

[0042] In some optional embodiments, referring to Figure 1 and Figure 2 As shown, the femtosecond laser processing system further includes an optical path adjustment module, which includes a shutter 31, which is arranged 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 pass or block the laser pulse.

[0043] Further, refer to Figure 1 and Figure 2 As shown, the optical path adjustment module also includes a plurality of optical path adjustment reflectors 32 for adjusting the direction of the optical path. Specifically, the number of the optical path adjustment reflectors 32 is three, which are specifically distributed between the half-wave plate 21 and the pulse separator 22, between the pulse separator 22 and the beam expander 23, and between the beam expander 23 and the spatial light modulator 24.

[0044] In some optional embodiments, referring to Figure 1 and Figure 2 As shown, the femtosecond laser processing system further includes a focusing observation module, which includes a white light source 41, an attenuation plate 42, a filter 43, a CCD camera 44 and an optical lens 45, and the optical path adjustment module further includes a visible light transmission laser reflector 33, a non-polarized white light beam splitter 34 and an objective lens 35. The spatial light modulator 24, the visible light transmission laser reflector 33 and the objective lens 35 are arranged in sequence, the non-polarized white light beam splitter 34 is arranged on one side of the visible light transmission laser reflector 33, and the white light source 41, the non-polarized white light beam splitter 34, the attenuation plate 42, the filter 43, the CCD camera 44 and the optical lens 45 are arranged in sequence. The laser pulse passes through the spatial light modulator 24 and the visible light transmission laser reflector 33 in sequence and then reaches the objective lens 35. 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, and the low-intensity refracted light passes through the attenuation plate 42 and the filter 43 in sequence to reach the CCD camera 44. Among them, the attenuation plate 42 and the filter 43 are used to convert the low-intensity refracted light output by the non-polarized white light beam splitter 34 into a signal that can be received and processed by 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, and observes whether the laser pulse is focused on the surface of the workpiece 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 from the spatial light modulator 24 is reflected to the objective lens 35 via the visible light transmission laser reflector 33, and finally focused on the surface of the workpiece. At the same time, 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, wherein the low-intensity reflected light is transmitted to the objective lens 35 via the visible light transmission laser reflector 33, and is also focused on the surface of the workpiece; while the low-intensity refracted light is processed by the attenuation plate 42 and the filter 43 in turn and enters the CCD camera 44, so as to observe the surface of the workpiece through the optical lens 45, thereby facilitating the finding of the processing position and the focus under high precision, and also allowing a certain degree of observation of the processed sample.

[0046] The present invention uses a non-polarized white light beam splitter 34 to separate low-intensity reflected light and refracted light, avoiding interference of high-energy laser on the CCD camera 44 and the optical lens 45, and realizing simultaneous processing and observation. Compared with the prior art that requires switching the optical path or pausing the processing to adjust the focus, the present invention ensures the stability of real-time monitoring through the splitting design.

[0047] In some optional embodiments, referring to Figure 1 and Figure 2 As shown, the femtosecond laser processing system also includes a workpiece processing module, which is arranged on the side of the objective lens 35 away from the visible light transmission laser reflector 33. The workpiece processing module includes a working container 51, a filter 52 and an air pump 53. The working container 51 is provided with a receiving cavity 511 for receiving the workpiece, and the air pump 53, the filter 52 and the receiving cavity 511 are connected in sequence. The air 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.

[0048] Specifically, the laser emitted by the laser emitting module 1 is sequentially pulse-separated and beam-shaped, and then the laser beam is focused onto the workpiece surface in the working container 51 through the objective lens 35. The working container 51 may be square in shape, and the vacuum pump 53 and the filter 52 may be sequentially connected to the gas outlet 513 of the working container 51, and the vacuum pump 53 may remove the toxic powder and gas generated during the processing in the working container 51, and the filter 52 may effectively filter the toxic powder extracted from the working container 51, and the filtering accuracy may be 0.2um.

[0049] When the femtosecond laser processing system of the present invention is used to process workpieces of specific materials (such as gallium arsenide), since gallium arsenide is a toxic substance, the powder generated during the processing is likely to affect the physical and mental health of the operator. The present invention uses an air pump 53 and a filter 52 to achieve synchronous detoxification during the processing process, while ensuring processing safety and surface quality.

[0050] In some optional embodiments, referring to Figure 3 As shown, the working container 51 of the embodiment of the present invention includes a first split portion 514 and a second split portion 515, and the first split portion 514 and the second split portion 515 are detachably connected and surround a receiving chamber 511. In an exemplary embodiment, referring to Figure 3 As shown, the first split part 514 and the second split part 515 can be rectangular blocks of equal size, each rectangular block has a groove of the same area, and the first split part 514 and the second split part 515 can be buckled up and down to be placed so that the two grooves are aligned and connected, thereby forming a receiving chamber 511. And the first split part 514 and the second split part 515 can be fixed by fastening members such as bolts at the four corners. By adopting a split design for the working container 51, it is convenient to place the workpiece, and the processing process of the workpiece can be carried out in a relatively sealed receiving chamber 511, avoiding the influence of external environmental factors on the processing process, thereby improving the processing quality of the nano-groove 7.

[0051] In some optional embodiments, referring to Figure 3As shown, the working container 51 also includes an optical glass piece 517 , the first split portion 514 is provided with an opening, the opening is communicated with the accommodating cavity 511 , the optical glass piece 517 is arranged at the opening, and the optical glass piece 517 is used to make the accommodating cavity 511 light-transmissive.

[0052] Specifically, the opening can be set in the middle area of ​​the upper surface of the first split portion 514, which is the laser irradiation area during the processing. The thickness of the optical glass sheet 517 can be 500um to 600um, and has good light transmittance of ultraviolet light, green light and infrared light. The light transmittance of the optical glass sheet 517 is conducive to the operator to observe the processing status of the workpiece in real time.

[0053] Further, in some optional embodiments, referring to Figure 3 As shown, an air inlet 512 and an air outlet 513 are respectively provided on the side wall of the working container 51 which is perpendicular to the incident direction of the laser pulse, and the air inlet 512 and the air outlet 513 are respectively connected to the accommodating cavity 511. When performing suction filtration, air enters from the air inlet 512 of the working container 51 and is discharged from the air outlet 513, so that the flow direction of the toxic powder is controllable to avoid affecting the laser processing process, and the end of the air pump 53 away from the filter 52 is connected to the air pipe and inserted into the water to play a double filtering role.

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

[0055] In some optional embodiments, referring to Figure 1 As shown, the workpiece processing module further includes a micro-nano workbench 54, on which the working container 51 is disposed, and the micro-nano workbench 54 is used to control the movement of the working container 51. Specifically, Figure 4 Schematic diagram of a processing route in one embodiment of the present invention. The direction of the arrow in the figure represents the moving direction of the micro-nano working table 54 when processing each row of nano-grooves 7. Figure 5 and Figure 6 The scanning electron microscope image and the transmission electron microscope image of the workpiece after laser processing are respectively shown. It should be understood that in the actual processing process, the micro-nano working table 54 can control the working container 51 to move along the processing path to complete the processing of the nano-groove array on the surface of the workpiece.

[0056] In some optional embodiments, referring to Figure 1 and Figure 2 As shown, the femtosecond laser processing system in the present invention also includes a power module 6, and the laser emission module 1, the shutter 31, the pulse separator 22, the white light source 41, the micro-nano workbench 54, the vacuum pump 53 and the CCD camera 44 are respectively connected to the power module 6, and the power module 6 is used to power the above structures.

[0057] In a second aspect, the present invention further provides a femtosecond laser processing method for processing the nano-grooves 7, and the femtosecond laser processing method is based on the above-mentioned femtosecond laser processing system. The femtosecond laser processing method comprises the following steps:

[0058] S1: First turn on the power module 6, the shutter 31, the white light source 41 in the focusing observation module and the CCD camera 44, place the workpiece in the accommodating cavity 511 in the working container 51, install the first split part 514 and the second split part 515, turn on the vacuum pump 53 and the filter 52, and connect the end of the vacuum 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 the shutter 31 to output low-power femtosecond laser, and adjust the positions of the beam expander 23 and each reflector so that the femtosecond laser spot is at the center of the beam expander 23 and each lens group. With the help of the focusing observation module, the femtosecond laser is vertically incident on the objective lens 35 and focused on the workpiece surface, and then turn off the laser emission module 1 and the shutter 31.

[0060] The present invention first pre-focuses with energy slightly higher than the ablation threshold to ensure the accuracy of the focal position of the light spot before switching to the required parameters for processing, thereby avoiding the risk of workpiece damage due to inaccurate focus and improving the yield rate.

[0061] S3: After setting the output parameters of the laser emission module 1 and the pulse delay time of the pulse separator 22, the laser emission module 1, the optical path adjustment module and the beam shaping module are turned on again, the half-wave plate 21 is rotated, the polarization state of the femtosecond laser is adjusted, and the workpiece is processed. When the workpiece is spliced, the micro-nano workbench 54 is controlled to move the workpiece at an interval of half a period or an odd multiple of a half a period.

[0062] It should be noted that splicing processing specifically refers to the process of performing multiple scans on different areas during large-area processing due to the limitation of the laser scanning range, and then splicing these different scanned areas together to form a larger area of ​​nano-groove array. The present invention uses a continuous processing method to achieve splicing of different scanned areas. In a specific embodiment, Figure 4In the figure, each row of nano-grooves 7 is a scanning area. Since the formation and arrangement of the nano-grooves 7 is achieved by moving the workpiece during the laser processing, the present invention controls the micro-nano workbench 54 to displace and move the workpiece at intervals of half a cycle or an odd multiple of a half cycle during the splicing process, that is, the interval between two adjacent scanning areas along the processing direction is half a cycle or an odd multiple of a half cycle, such as half a cycle, two thirds of a cycle, etc. Among them, the sum of the width of each nano-groove 7 and the distance between two adjacent nano-grooves 7 in each scanning area is the moving distance of one cycle, such as Figure 4 As shown, T / 2 refers to the moving distance of half a cycle, and T refers to the moving distance of one cycle.

[0063] The present invention adopts staggered processing to splice different scanning areas, which is beneficial to avoid the half-period mismatch phenomenon during the processing of the nano-grooves 7 and reduce the bending mismatch between nano-grooves 7 in different rows. It should be noted that the half-period mismatch phenomenon refers to the fact that during the femtosecond laser processing, the residual heat of adjacent pulses at a high repetition frequency will still form a temperature gradient on the surface of the material. When the processing area moves to an adjacent position, the thermal expansion of the previous processing area will change the dielectric constant of the local material, resulting in a change in the propagation speed of the surface plasmon wave (SPP), thereby destroying the interference condition between the laser and the SPP and causing a periodic phase shift. Alternatively, the non-uniform stress generated by the processing material after being heated will cause microscopic deformation, causing the formed nano-grooves 7 to be compressed or stretched at the edges. If directly spliced ​​continuously, the periodic phases of the new and old areas cannot be aligned, resulting in a half-period misalignment at the splicing. Refer to Figure 5 and Figure 6 As shown, the present invention suppresses the thermal effect during the processing by means of half-cycle or odd-multiple half-cycle misalignment splicing processing, optimizes the splicing offset, improves the consistency of the nano-groove array, and solves the problem of half-cycle mismatch generated during the processing.

[0064] Further, in step S3, the output parameters of the laser emission module 1 include: the minimum pulse width is 255fs, the fundamental wavelength is 1030nm, and the corresponding maximum output power is 16W; the doubled frequency laser wavelength is 515nm, and the output power is 6W; the quadruple frequency laser wavelength is 257nm, the output power is 1W, the laser frequency is 1KHz to 1100KHz, and the scanning speed is adjustable from 0.1mm / s to 80mm / s. The pulse separator 22 introduces a delay time of ±14ps between the split pulses. Preferably, the fundamental wavelength is selected to be 1030nm, the output power is 160mW, the laser frequency is 1MHz, the scanning interval is 1.2um, the scanning speed is 10mm / s, and the delay time of the pulse separator is set to 8ps. The present invention takes the above-mentioned laser output parameters and the delay time parameters introduced during pulse separation as an example, and processes gallium arsenide materials so that the prepared nano-groove array is effectively improved in terms of minimum line width, regularity, and aspect ratio.

[0065] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A femtosecond laser processing system, characterized in that: It comprises a laser emission module (1) and a beam shaping module, wherein the beam shaping module comprises a pulse separator (22), a spatial light modulator (24) and a beam expander (23), and the laser emission module (1), the pulse separator (22), the beam expander (23) and the spatial light modulator (24) are arranged in sequence; The laser emission module (1) is used to emit laser pulses, and the laser pulses sequentially pass through the pulse separator (22) and the beam expander (23) before reaching the spatial light modulator (24). The pulse separator (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, and the spatial light modulator (24) is used to shape a Gaussian beam into a flat-top beam.

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

3. The femtosecond laser processing system according to claim 1, characterized in that: The femtosecond laser processing system also includes a workpiece processing module; The workpiece processing module comprises a working container (51), a filter (52) and an air pump (53); a receiving cavity (511) for receiving the workpiece is provided in the working container (51); The vacuum pump (53), the filter (52) and the accommodating chamber (511) are connected in sequence; the vacuum pump (53) is used to extract powder and gas generated in the accommodating chamber (511) during workpiece processing; and the filter (52) is used to filter the extracted powder.

4. The femtosecond laser processing system according to claim 3, characterized in that: The working container (51) comprises a first split portion (514) and a second split portion (515), wherein the first split portion (514) and the second split portion (515) are detachably connected and enclose the accommodating chamber (511).

5. The femtosecond laser processing system according to claim 4, characterized in that: The working container (51) further comprises an optical glass sheet (517); the first split portion (514) is provided with an opening, the opening is communicated with the accommodating cavity (511); the optical glass sheet (517) is arranged at the opening, and the optical glass sheet (517) is used to allow light to pass through the accommodating cavity (511).

6. The femtosecond laser processing system according to claim 5, characterized in that: An air inlet (512) and an air outlet (513) are respectively provided on two side walls of the working container (51) perpendicular to the incident direction of the laser pulse, the air inlet (512) and the air outlet (513) are respectively connected to the accommodating cavity (511), and 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 sheet (517) and the first split portion (514).

7. The femtosecond laser processing system according to claim 3, characterized in that: The workpiece processing module further comprises a micro-nano workbench (54), the working container (51) is arranged on the micro-nano workbench (54), and the micro-nano workbench (54) is used to control the movement of the working container (51).

8. The femtosecond laser processing system according to claim 1, characterized in that: The femtosecond laser processing system further comprises a focusing observation module and an optical path adjustment module, wherein the focusing observation module comprises a white light source (41), an attenuation plate (42), a filter (43) and a CCD camera (44), and the optical path adjustment module comprises a visible light transmission laser reflector (33), a non-polarized white light beam splitter (34) and an objective lens (35); The laser pulse passes through the spatial light modulator (24) and the visible light transmission laser reflector (33) in sequence before reaching the objective lens (35); 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) before reaching the objective lens (35); the low-intensity refracted light passes through the attenuation plate (42) and the filter (43) in sequence before reaching the CCD camera (44); the CCD camera (44) is used to receive and process an optical signal formed by the transformation of the low-intensity refracted light so as to observe the focusing condition of the laser pulse.

9. A femtosecond laser processing method, characterized in that: The femtosecond laser processing method is based on the femtosecond laser processing system according to any one of claims 1 to 8, and the femtosecond laser processing method comprises: After placing the workpiece in the working container (51), the vacuum pump (53) and the filter (52) are turned on; Turning on the laser emission module (1) to output femtosecond laser light so that the femtosecond laser light is vertically incident on the objective lens (35) and focused on the surface of the workpiece, and then turning off the laser emission module (1); After setting the output parameters of the laser emission module (1) and the pulse delay time of the pulse separator (22), the laser emission module (1), the optical path adjustment module and the beam shaping module are reopened to process the workpiece; When the workpieces are spliced, the micro-nano worktable (54) is controlled to move the workpieces at intervals of half a period or an odd multiple of a half a period.

10. The femtosecond laser processing method according to claim 9, characterized in that: 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 doubled frequency laser wavelength of 515 nm, an output power of 6 W, a quadrupled frequency laser wavelength of 257 nm, 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.

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