A laser micro-machining system and method

Abstract

The application provides a laser micro-processing system and method, wherein the laser micro-processing system comprises a laser, a beam expander, a half-wave plate, a one-dimensional AOD, a slit diaphragm, a dove prism, a 4f imaging system and a focusing lens for processing. The laser is used for emitting a laser beam; the beam expander is used for expanding and collimating the laser beam output by the laser; the half-wave plate is used for adjusting the polarization direction of incident light; the one-dimensional AOD is used for diffracting incident laser; the slit diaphragm is used for filtering out unnecessary diffracted light; the dove prism is used for controlling the rotation of the outgoing light; the 4f imaging system is used for imaging the light field distribution of the outgoing surface of the dove prism to the entrance pupil surface of the focusing lens for processing; and the focusing lens for processing is used for converging the laser beam into a focal spot to act on the processing surface of the sample. The laser micro-processing system and method solve the problems of complex structure, high control difficulty and low diffraction efficiency of the two-dimensional AOD system, and realize high-speed, high-precision and adjustable aperture processing of micro-holes.

Description

Technical Field

[0001] This invention relates to the field of laser processing technology, and in particular to a laser micromachining system and method. Background Technology

[0002] Laser micro-hole processing has wide applications in aerospace, medical devices, semiconductors, and precision instruments. With the increasing integration of devices, higher demands are being placed on the size, roundness, taper, and processing efficiency of micro-holes. When the micro-hole diameter is less than 15μm, the traditional galvanometer scanning processing method used in laser processing equipment has the following drawbacks: (1) Dynamic limitation of galvanometer: When the X-axis galvanometer and Y-axis galvanometer work together to scan the micro-trajectory, the speed and acceleration are very low due to mechanical inertia. This not only results in low processing efficiency but also insufficient control precision, leading to poor roundness of the micro-holes and obvious thermal ablation effect.

[0003] (2) Ellipticity of the laser beam: Since the output beam of the laser has a certain ellipticity and the beam expansion system will also introduce astigmatism, the focused spot will be elliptical, which will further degrade the roundness of the micro-aperture.

[0004] (3) The two-dimensional acousto-optic deflector (AOD) system is complex: Although the two-dimensional acousto-optic deflector (AOD) can achieve high-speed scanning, it requires two orthogonally set one-dimensional AODs to work together. The control logic is complex, the parameters are difficult to decouple, the software development is extremely difficult, and the diffraction efficiency is low, resulting in a large loss of laser power / single pulse energy, which limits its application.

[0005] (4) It is difficult to balance processing accuracy and efficiency: The traditional scanning processing system composed of galvanometer and field mirror is efficient when processing large-format images, but when processing micro-holes at the micrometer scale, it is not only inaccurate but also inefficient; the two-dimensional AOD system is highly accurate but has a small scanning angle, making it difficult to balance large-format continuous processing. Summary of the Invention

[0006] This invention provides a laser micromachining system and method that can effectively eliminate beam elliptic aberration, obtain a true circular focal spot at the micrometer scale, and achieve high speed, high precision, and flexible adjustment of the processing aperture for micro-holes.

[0007] The technical solution adopted in this invention is as follows: a laser micromachining system, comprising: a laser, a control system, a beam expander, a half-wave plate, a one-dimensional AOD, a slit aperture, a Dove prism, a 4f imaging system, and a focusing lens for processing, arranged sequentially along the optical path; the control system is electrically connected to the laser, the one-dimensional AOD, and the rotating motor. The laser is configured to emit a laser beam with a Gaussian intensity distribution; the beam expander is used to expand, collimate, and control the divergence angle of the laser beam output by the laser, so that the diameter of the output beam matches the incident diameter of the one-dimensional AOD. The half-wave plate is used to adjust the polarization direction of the incident light to match the incident conditions of the one-dimensional AOD; the one-dimensional AOD is used to convert the radio frequency driving signal into ultrasonic waves in the crystal, form a Bragg diffraction grating in the crystal, and diffract the incident laser. The slit stop is used to filter out unwanted diffraction light, allowing only the +1st order diffraction light to enter the Dove prism; The Dowell prism is coaxially mounted at the center of the rotor of a rotary motor; when the rotary motor drives the Dowell prism to rotate at an angular velocity ω, the emitted beam rotates at a high speed around its optical axis at an angular velocity of 2ω. The 4f imaging system is used to image the light field distribution of the exit surface of the Dowell prism onto the entrance pupil surface of the processing focusing lens; the processing focusing lens is used to focus the laser beam, which has been rotated and controlled by the Dowell prism, into a focal spot and apply it to the processing surface of the sample.

[0008] Furthermore, the control system has a pre-stored database of "target aperture - AOD driving frequency" mapping relationships.

[0009] Furthermore, the 4f imaging system includes a first focusing lens and a second focusing lens, wherein the first focusing lens, the second focusing lens, and the processing focusing lens are coaxial.

[0010] Furthermore, the focal length of the first focusing lens is F1, and the focal length of the second focusing lens is F2; ​​the 4f imaging system images the high-speed rotating beam emitted from the Dowell prism onto the entrance pupil of the processing focusing lens in a ratio of F2 / F1.

[0011] Furthermore, it also includes a first reflecting mirror and a second reflecting mirror arranged along the optical path between the beam expander and the half-wave plate. The first reflecting mirror and the second reflecting mirror are used to adjust the transmission direction of the laser beam and provide fine-tuning dimension so that the laser beam is incident on the one-dimensional AOD at a preset angle.

[0012] Furthermore, it also includes a third reflecting mirror arranged along the optical path between the Dove prism and the first focusing mirror. The third reflecting mirror is used to adjust the transmission direction of the laser beam and provide fine-tuning dimension, so that the laser beam is incident on the first focusing mirror and the second focusing mirror in a direction that coincides with the optical axis of the first focusing mirror and the second focusing mirror.

[0013] Furthermore, a fourth reflecting mirror is provided between the first focusing mirror and the second focusing mirror, and the fourth reflecting mirror is used to adjust the beam transmission direction.

[0014] Furthermore, a scanning galvanometer is provided between the second focusing lens and the processing focusing lens. The scanning galvanometer is used to perform rapid and precise scanning control of the light beam within the scanning area of ​​the processing focusing lens, so as to achieve precise positioning of the position to be processed.

[0015] This invention also provides the following technical solutions: A laser micromachining method using the aforementioned laser micromachining system, characterized by comprising the following steps: S1: The control system issues a command to start the high-speed rotating motor to drive the Daowei prism to rotate at a preset angular velocity ω; S2: The original beam output by the laser is expanded and collimated by a beam expander, and after being polarized by a half-wave plate, it is incident on a one-dimensional AOD at a preset angle; S3: The control system sends the corresponding driving frequency and frequency change to the one-dimensional AOD according to the preset target machining aperture; the one-dimensional AOD generates +1 order diffracted light and emits it at a specific diffraction angle, causing the beam to deviate from the center of the optical axis by a certain angle. S4: The +1st order diffracted light, which is off-center from the optical axis, is filtered through a slit aperture until it is filtered out of order and then incident on a high-speed rotating Dowell prism; the Dowell prism rotates at an angular velocity ω, and the outgoing beam rotates at a high speed at an angular velocity of 2ω. S5: The high-speed rotating beam enters the 4f imaging system and is precisely imaged onto the entrance pupil of the focusing lens used for processing. At the same time, it is scaled up by the F2 / F1 ratio and then enters the focusing lens. S6: The focusing lens used in the processing focuses the light beam onto the processing surface of the sample, forming a micron-scale, time-averaged equivalent circular focal spot.

[0016] Furthermore, the control system is electrically connected to a motion platform, and the sample is placed on the motion platform. The system also includes the following steps: S7: The control system drives the motion platform to move the sample along a preset trajectory. At the same time, the one-dimensional AOD synchronously adjusts the driving frequency and power to process micropores of different diameters and precisions.

[0017] Compared to existing technologies, the laser micromachining system and method of this invention decouples and coordinates a one-dimensional aperture head (AOD) with a Dowell prism. The one-dimensional AOD is only responsible for adjusting the diffraction angle in a single dimension to control the aperture, while the Dowell prism is responsible for the high-speed rotation of the laser beam to eliminate the effects of ellipticity of the laser beam and aberrations in the optical path system. The two functions are independent and do not interfere with each other. Compared to traditional two-dimensional AOD systems, complex polarization adjustment and dual-axis synchronous control are not required, simplifying the structure and significantly reducing the control difficulty. Moreover, the high-speed rotation of the Dowell prism transforms the static elliptical spot into an ideal circular focal spot under time averaging, directly eliminating the poor roundness of the laser output beam and the distortion and astigmatism caused by the adjustment of the beam expander system, eliminating elliptic aberrations, and effectively ensuring the true roundness of the micro-hole processing. In addition, the 4f imaging system accurately images the light field distribution of the Dowell prism exit surface onto the entrance pupil surface of the focusing lens used for processing, eliminating diffraction effects. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but should not be construed as limiting the invention. In the drawings, Figure 1 : A schematic diagram of the structure of Embodiment 1 of the laser micromachining system of the present invention; Figure 2 : Schematic diagram of the working principle of the one-dimensional acousto-optic deflector of the present invention; Figure 3 : Schematic diagram of the image rotation principle of the Dowell prism of this invention; Figure 4 : Schematic diagram of the change in beam cross-sectional shape before and after rotation of the Dowell prism in this invention; Figure 5 : Schematic diagram of the optical structure and beam transmission principle of the 4f imaging system of the present invention; Figure 6 : A schematic diagram of the structure of Embodiment 2 of the laser micromachining system of the present invention; Figure 7 : Flowchart of the laser processing method of the present invention.

[0019] Names and numbers of each component 1. Laser; 2. Beam expander; 3. First reflector; 4. Second reflector; 5. Half-wave plate; 6. One-dimensional AOD; 7. Slit aperture; 8. Dowell prism; 9. Rotary motor; 10. Third reflector; 11. First focusing lens; 12. Second focusing lens; 13. Processing focusing lens; 14. Sample; 15. Motion platform; 16. Control system; 17. Fourth reflector; 18. Scanning galvanometer. Detailed Implementation

[0020] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0021] Example 1 like Figure 1 As shown, the laser micromachining system of the present invention includes a laser 1, a beam expander 2, a first reflector 3, a second reflector 4, a half-wave plate 5, a one-dimensional acousto-optic deflector 6 (hereinafter referred to as one-dimensional AOD), a slit aperture 7, a Dowell prism 8, a rotary motor 9, a third reflector 10, a first focusing lens 11, a second focusing lens 12, a processing focusing lens 13, a sample 14, a motion platform 15, and a control system 16, arranged sequentially along the optical path.

[0022] The control system 16 is a computer or embedded motion controller, electrically connected to the laser 1, the one-dimensional AOD 6, the rotary motor 9, and the motion platform 15, for coordinated control of the timing and parameters of each module. Furthermore, the control system 16 has a pre-stored database of "target aperture - AOD driving frequency" mapping relationships, which can calculate the corresponding driving frequency command in real time based on preset micro-hole processing parameters by looking up the table or using the difference, and can control the driving power of the one-dimensional AOD 6 to adjust the diffraction efficiency.

[0023] Laser 1 is configured to emit a laser beam with a Gaussian intensity distribution for outputting high-quality pulsed laser. Laser 1 can be a femtosecond laser (pulse width <1ps), a picosecond laser (pulse width 1ps~1000ps), or a nanosecond laser (pulse width >1ns), with an output wavelength between 180nm and 1600nm, a diameter less than 5mm, and a linear polarization state.

[0024] The beam expander 2 is used to expand, collimate, and control the divergence angle of the laser beam output from the laser 1, so that the output beam diameter matches the optimal incident diameter of the one-dimensional AOD 6. Its beam expansion factor can be continuously adjusted within the range of 0.5 to 10 times.

[0025] The first reflector 3 and the second reflector 4 are both high-reflectivity dielectric mirrors (reflectivity > 99.5%), used to adjust the transmission direction of the laser beam and provide fine-tuning dimension so that the laser beam is precisely incident on the one-dimensional AOD 6 at the designed angle.

[0026] The half-wave plate 5 is used to adjust the polarization direction of the incident light to match the incident conditions of the one-dimensional AOD 6.

[0027] The one-dimensional AOD 6 is positioned in the outgoing light path of the second reflector 4. It is responsible for adjusting the diffraction angle in only one dimension to control the aperture. Its core component is an acousto-optic crystal (such as sapphire, tellurium dioxide (TeO2), or fused silica glass). Its operating wavelength is 200nm to 1600nm, its operating frequency is between 30MHz and 500MHz, its frequency resolution is greater than or equal to 1kHz, its frequency refresh interval is less than 1μs, and its window size is less than 10mm. The one-dimensional AOD 6 converts the radio frequency drive signal into ultrasonic waves within the crystal through a piezoelectric transducer, forming a Bragg diffraction grating within the crystal to diffract the incident laser.

[0028] The control system 16 sends a corresponding driving frequency command to the one-dimensional AOD 6 according to the preset target processing aperture, so that the +1st order diffracted light deviates from the optical axis center by a certain angle; the one-dimensional AOD 6 only controls the deflection of the beam along a single dimension, without the need for two-dimensional synchronization.

[0029] like Figure 2 As shown, Figure 2 This is a schematic diagram illustrating the working principle of a one-dimensional AOD, showing the change in diffraction angle θ when the driving frequency f is changed. The values ​​fL, f0, and f in the diagram are... H These represent the lowest driving frequency, the center driving frequency, and the highest driving frequency, respectively; δ is the incident angle, and θ1 is the diffraction angle. The diffraction angle θ1 and the driving frequency f satisfy the Bragg condition: θ1≈ λ·f / ν, Where λ is the laser wavelength and ν is the speed at which sound waves propagate in the crystal.

[0030] By changing the driving frequency f, the diffraction angle of the +1st order diffracted light can be precisely controlled. When the driving frequency changes by Δf, the diffraction angle changes by Δθ1 = λ·Δf / ν.

[0031] The slit aperture 7 is set in the outgoing light path of the one-dimensional AOD 6 and is located in front of the Daowei prism 8. It is used to filter out unwanted diffraction light such as the 0th order, -1st order, and ±2nd order, and only retain the +1st order diffraction light to enter the Daowei prism 8, effectively avoiding stray light interference with processing quality.

[0032] like Figure 1 , Figure 3 and Figure 4 As shown, the Dowell prism 8 is positioned in the exit light path of the slit aperture 7 and acts as an image rotator. After light passes through the Dowell prism 8, the resulting image rotates 180° around its optical axis; and the Dowell prism 8 is coaxially mounted at the rotor center of the rotary motor 9, with their optical axes strictly coincident. The rotary motor 9 is a high-precision hollow shaft servo motor or torque motor, capable of driving the Dowell prism 8 to rotate at a high speed around its optical axis at an angular velocity ω.

[0033] The rotational speed of the rotary motor 9 can be continuously adjusted within the range of 0 to 50,000 rpm. When the rotary motor 9 drives the Dowell prism 8 to rotate at an angular velocity ω, the emitted beam rotates at a high speed around its optical axis (i.e., the rotor center) at an angular velocity of 2ω.

[0034] like Figure 1 and Figure 5 As shown, the third reflecting mirror 10 is used to adjust the transmission direction of the laser beam and provide fine-tuning dimension so that the laser beam is precisely incident on the first focusing mirror 11 and the second focusing mirror 12 at a designed angle (i.e., the direction in which the optical axes of the first focusing mirror 11 and the second focusing mirror 12 coincide). The first focusing mirror 11 and the second focusing mirror 12 form a 4f imaging system, wherein the focal length of the first focusing mirror 11 is F1 and the focal length of the second focusing mirror 12 is F2.

[0035] It is worth noting that, in this embodiment, the optical arrangement of the first focusing lens 11 and the second focusing lens 12 should satisfy the following: ① The distance between the front focal point of the first focusing lens 11 and the center of the Dowell prism 8 is: L+F1 (L is the optical path from the exit surface of the Dowell prism 8 to the front focal point of the first focusing lens 11). ② The rear focal plane of the first focusing lens 11 coincides with the front focal plane of the second focusing lens 12; the rear focal plane of the second focusing lens 12 coincides with the front focal plane of the processing focusing lens 13; ③ The first focusing lens 11, the second focusing lens 12, and the processing focusing lens 13 are coaxial.

[0036] The 4f imaging system in this embodiment has the following three main functions: (1) The light field distribution of the exit surface of the Dowell prism 8 is accurately imaged onto the entrance pupil surface of the focusing lens 13 used for processing to eliminate the diffraction effect; (2) By selecting the focal length ratio F2 / F1, the spot size is scaled to best match the entrance pupil diameter of the focusing lens 13 used for processing; (3) Naturally filter out high-frequency diffraction noise on the spatial spectrum surface.

[0037] The 4f imaging system images the high-speed rotating beam emitted from the Dowell prism 8 onto the entrance pupil of the processing focusing lens 13 at a ratio of F2 / F1, thereby eliminating diffraction effects and optimizing the light field distribution.

[0038] like Figure 1 As shown, the processing focusing lens 13 is set in the output optical path of the 4f imaging system to focus the rotated laser beam into a micron-scale focal spot, which acts on the processing surface of the sample 14 to produce a micron-scale or even submicron-scale true circular focal spot.

[0039] The motion platform 15 is used to support the sample 14 and can perform one-dimensional, two-dimensional, or three-dimensional precision motion relative to the focal spot. The motion platform 15 can be a nanoplatform, an air-bearing platform, a linear motor platform, or a motion module. In this embodiment, the motion platform 15 preferably uses a high-precision linear motor platform with a motion accuracy of sub-micron level and a motion range of 300mm × 300mm. The sample 14 can be made of metal (stainless steel, aluminum alloy, etc.), ceramic (alumina, zirconium oxide, etc.), semiconductor (such as silicon (Si), silicon carbide (SiC), gallium arsenide (GaAs), etc.), or polymer materials, and is not limited thereto.

[0040] The working principle of the laser micromachining system in this embodiment is as follows: The control system 16 controls the original beam output by the laser 1 to be expanded and collimated by the beam expander 2, and then guided by the first reflector 3 and the second reflector 4. After the polarization direction is adjusted by the half-wave plate 5, it is incident on the one-dimensional AOD 6 at the designed angle and polarization direction. The control system 16 sends a corresponding driving frequency signal to the one-dimensional AOD 6 according to the preset target processing aperture, and changes the diffraction angle of the +1st order diffracted light. The change in the diffraction angle causes the outgoing beam to deviate from the center of the optical axis by a certain distance. This deviation distance is magnified by the subsequent 4f imaging system and the processing focusing lens 13, which determines the scanning radius of the focused spot on the sample surface, thereby achieving precise control of the processing aperture. Meanwhile, the control system 16 drives the rotary motor 9 to rotate the Dowell prism 8 at a preset angular velocity ω around the optical axis at high speed; according to the image rotation characteristics of the Dowell prism 8, when the Dowell prism 8 rotates by an angle θ2, the rotation of the emitted image is 2θ2 (please refer to...). Figure 3 , Figure 3 This is a schematic diagram illustrating the image rotation principle of the Dowell prism 8, showing that the emitted beam rotates by an angle of 2θ2 when the Dowell prism 8 rotates by an angle of θ2. Therefore, the +1st order diffracted spot (already deviated from the optical axis center) after being modulated by the one-dimensional AOD 6 rotates at a high speed around the optical axis with an angular velocity of 2ω after passing through the Dowell prism 8 (please refer to...). Figure 4 , Figure 4 The diagram shows the change in beam cross-sectional shape before and after the rotation of the Daowei prism 8, demonstrating that the elliptical beam spot is equivalent to a circular focal spot after high-speed rotation; (a) is a schematic diagram of the elliptical beam spot; (b) is a schematic diagram of the change in beam cross-sectional shape before and after the rotation of the Daowei prism 8. During this process, the Daowei prism 8 maintains high-speed rotation, while the one-dimensional AOD 6 is only responsible for adjusting the diffraction angle of the output beam by changing the driving frequency. The two functions are decoupled and do not interfere with each other. A high-speed rotating light beam enters a 4f imaging system consisting of a first focusing mirror 11 and a second focusing mirror 12 (see reference). Figure 5 , Figure 5(This is a schematic diagram of the optical structure and beam transmission principle of the 4f imaging system). The 4f imaging system accurately images the light field distribution of the exit surface of the Dowell prism 8 onto the entrance pupil surface of the processing focusing lens 13. At the same time, it scales the spot size by using the focal length ratio F2 / F1 and filters out high-frequency diffraction noise on the spatial spectrum surface. The high-speed rotating beam optimized by the 4f imaging system is focused by the processing focusing lens 13 onto the processing surface of the sample 14 to form a micron-scale true circular focal spot.

[0041] Therefore, when the Dowell prism 8 rotates at a sufficiently high speed (e.g., speed > 10000 rpm), the ellipticity of the output spot of the laser 1 under static conditions and the astigmatism accumulated in the optical path will be completely canceled out under the time averaging effect, forming a rotationally symmetrical ideal circular focal spot (i.e., a true circular focal spot) on the focal plane; the true circular focal spot is scanned along the preset processing trajectory to obtain a micro-hole with high roundness and low thermal influence.

[0042] 1. The calculation process for aperture control and focus offset is as follows: Let the driving frequency of the one-dimensional AOD6 be f, and the center frequency be f0. Then the change in driving frequency Δf = f - f0. Let the velocity of sound in the acousto-optic crystal be ν, and the laser wavelength be λ. Then the change in diffraction angle Δθ1 of the +1st order diffracted light satisfies: Δθ1=λΔf / ν The change in diffraction angle causes the outgoing beam to deviate from the optical axis center by an angle Δθ1. After being rotated by the Dowell prism 8, the beam rotates at an angular velocity of 2ω and then enters the 4f imaging system. After passing through the 4f imaging system, the angular magnification of the beam is N=F2 / F1. Therefore, the beam tilt angle when entering the processing focusing lens 13 is: θ in =Δθ1 N=λΔf / ν F2 / F1=λΔf F2 / (νF1) Since the focal length of the focusing lens 13 used in the processing is F3, the radius r of the focal point on the focal plane deviating from the center of the optical axis is: r=F3 |tan(θ in )|≈F3 θ in =F3 λΔfF2 / (νF1) When the driving frequency changes by Δf, the focal point draws a circle with radius r on the focal plane. The diameter of this circle is the aperture D of the micro-hole being processed. hole : D hole =2r+Ø=2 F3 λΔfF2 / (νF1)+Ø Where Ø is the diameter of the focused spot of the focusing lens 13 used for processing, and its calculation formula is as follows: Ø=4M 2 λF3 / (πD) Where M² is the laser beam quality factor, λ is the laser operating wavelength, F3 is the focal length of the focusing lens, and D is the diameter of the beam incident on the focusing lens (after beam expansion and scaling by the 4f imaging system).

[0043] In summary, the aperture diameter can be linearly adjusted by changing Δf. When Δf=0 (i.e., the one-dimensional AOD 6 is working at the center frequency), r=0, and the focal point is located at the center of the optical axis. If scanning is not performed at this time, a single-point micro-hole is processed, and the aperture diameter is determined by the focused spot itself.

[0044] 2. The aperture adjustment verification process is as follows: With F1=100mm, F2=200mm, and the spot magnification factor of 2, the focusing lens 13 used for processing adopts a telecentric field lens with a focal length of F3=100mm and the wavelength of laser 1 λ=355nm. (1) Focused spot diameter Ø The beam diameter D incident on the focusing lens 13 for processing, after being expanded by the beam expander 2 and scaled by the 4f imaging system, is approximately 8mm. Therefore, the theoretical spot diameter Ø is: Ø=4M 2 λF3 / (πD) With M²=1.2, λ=355nm, F3=100mm, and D=8mm, then Ø≈6.78μm; In actual processing, due to the rotation of the Daowei prism 8 to eliminate aberrations, the spot roundness is extremely high.

[0045] (2) Focal scanning radius r According to theoretical derivation, when the driving frequency changes by Δf, the focal point draws a circle with radius r on the focal plane: r=F3 λΔfF2 / (νF1) Taking typical parameters: λ=355nm, ν=5740m / s, F1=100mm, F2=200mm, F3=100mm, then: r =100mm×355×10 9 m / (5740m / s)×Δ f ×200mm / 100mm ≈1.2369×10 8 Δ f (mm) = 1.2369 × 10 5 Δ f (μm) That is, for every 1 kHz change in Δf, the radius of the circle scanned by the focal spot of the focusing lens on the sample increases by approximately 1.2369 × 10⁻⁶. 2 μm, or 12.369nm.

[0046] (3) Processing micropore diameter D hole When the driving frequency changes by Δf, the focal point draws a circle with radius r on the focal plane. The diameter of this circle is the aperture D of the micro-hole being processed. hole : D hole =2r+Ø=2 F3 λΔfF2 / (νF1)+Ø From the above data, we can obtain: (a) When Δf = 0 kHz, i.e., the input frequency is the center frequency, the aperture D of the processed micro-hole is... hole =Ø=6.78μm, meaning the smallest micro-circular hole diameter that can be processed is 6.78μm; (b) When Δf = 1 kHz, the aperture D of the micropore is processed. hole =2r+Ø≈6.8047μm, that is, for every 1kHz increase in driving frequency f, the aperture of the processed micropore increases by 2r=24.74nm; (c) When Δf = 50MHz, the aperture D of the micro-orifice is processed. hole =2r+Ø≈1243.6800μm≈1.244mm.

[0047] In other words, increasing the driving frequency f enables the fabrication of microholes from the micrometer to the millimeter level.

[0048] In summary, the laser micromachining system of this embodiment can be used for microhole machining tests, achieving microhole machining from the micrometer scale to the millimeter scale, with a theoretical aperture accuracy of up to 24.74 nm, which is nearly two orders of magnitude higher than the machining accuracy of traditional scanning systems composed of galvanometers and field mirrors.

[0049] like Figure 1 In another example, the focusing lens 13 for processing is replaced from a telecentric field lens with a high-magnification objective lens, and the laser 1 is an ultraviolet femtosecond laser to achieve precision processing of submicron or even hundred-nanometer-scale true circular microholes.

[0050] The numerical aperture (NA) of the high-magnification objective lens ranges from 0.05 to 1.4, preferably ≥ 0.65, and its focal length (F4) ranges from 3 mm to 50 mm. The front focal plane of the high-magnification objective lens coincides with the rear focal plane of the second focusing lens 12, i.e., the distance between them is F2 + F4. The high-magnification objective lens is used to converge the light beam, which has been rotated and controlled by the 4f imaging system, onto the processing surface of the sample 14, forming an ultra-fine, perfectly circular focal spot at the sub-micron or even nanometer scale.

[0051] Using the same workflow as in Example 1, micro-circular hole processing at the sub-micron or even nanometer level can be achieved. The calculation process for the processing hole diameter range and processing hole diameter accuracy is as follows: (1) Focused spot diameter Ø After beam expansion and scaling by the 4f system, the diameter D of the beam incident on the high-power objective lens is NA=0.65 and F4=4mm, then D=2×NA×F4=5.2mm; The focusing spot diameter Ø of a high-magnification objective lens is calculated using the following formula: Ø=4λF4 / (πD) Given λ = 343 nm, F4 = 4 mm, and D = 5.2 mm, then Ø ≈ 0.33610 μm = 336.10 nm.

[0052] (2) Focal scanning radius r According to theoretical derivation, when the driving frequency changes by Δf, the focal point draws a circle with radius r on the focal plane: r=F4 λΔfF2 / (νF1) Taking typical parameters: λ=343nm, ν=5740m / s, F1=100mm, F2=200mm, F4=4mm, then: r=4mm×343×10 9 m / (5740m / s)×Δf×200mm / 100mm ≈4.7804×10 10 Δf (mm) = 4.7804 × 10 7 Δf (μm) That is, for every 1 kHz change in Δf, the radius of the circle scanned on the sample by the high-power objective lens focal spot increases by approximately 4.7804 × 10⁻⁶. 4 nm.

[0053] (3) Processing micropore diameter D hole When the driving frequency changes by Δf, the focal point draws a circle with radius r on the focal plane. The diameter of this circle is the aperture D of the micro-hole being processed. hole : D hole =2r+Ø=2 F4 λΔfF2 / (νF1)+Ø From the above data, we can obtain: ① When Δf = 0kHz, i.e., the input frequency is the center frequency, the aperture D of the processed micro-hole is... hole =Ø=336.10nm, meaning the smallest micro-circular hole diameter that can be processed is 336.10nm; ② When Δf = 1kHz, the aperture D of the micropore being processed hole =2r+Ø≈0.3371μm, meaning that for every 1kHz increase in driving frequency f, the diameter of the processed micro-hole increases by 2r=9.5608×10 4 nm; ③ When Δf = 50MHz, the aperture D of the micro-orifice is processed. hole =2r+Ø≈48.1401μm.

[0054] In other words, increasing the driving frequency f enables the fabrication of micropores from the level of hundreds of nanometers to micrometers.

[0055] The laser micromachining system described in this example was used for micro-hole fabrication testing, enabling the fabrication of micro-holes from the scale of hundreds of nanometers to micrometers, with a theoretical aperture accuracy as high as 9.5608 × 10⁻⁶. 4 nm.

[0056] In summary, when the focusing lens 13 for processing is a telecentric field lens, the typical minimum spot diameter can be as small as 7 μm; when the focusing lens 13 for processing is a high-magnification objective lens, the theoretical minimum spot diameter can be as small as 300 nm. Therefore, by combining material damage threshold and process parameter optimization, the laser micromachining system of this embodiment can realize the processing of micro-circular holes with apertures of hundreds of nanometers.

[0057] Example 2 like Figure 6 As shown, the structure in this embodiment is the same as that in Embodiment 1 and will not be described again. The difference is that a fourth reflecting mirror 17 is added between the first focusing mirror 11 and the second focusing mirror 12 to adjust the beam transmission direction. A scanning galvanometer 18 is added between the second focusing mirror 12 and the processing focusing mirror 13. The scanning galvanometer 18 is a two-dimensional high-speed scanning galvanometer, which is used to quickly and accurately scan and control the beam within the scanning area of ​​the processing focusing mirror 13 to achieve precise positioning of the position to be processed.

[0058] The working process of the laser micromachining system in this embodiment is as follows: During the processing, the Daowei prism 8 maintains high-speed rotation, and the one-dimensional AOD 6 adjusts the processing aperture by changing the input drive frequency (as described in Example 1). The scanning galvanometer 18 adjusts the processing position of the microhole within the field of view of the focusing lens 13 by controlling the scanning center, thereby achieving rapid multi-point drilling within a single area. After the processing task within a scanning area of ​​one field lens (e.g., 40mm×40mm) is completed, the sample 14 is moved to the next processing area by the motion platform 15, and the processing is repeated to achieve high efficiency, high speed and large-area drilling.

[0059] In this embodiment, the target micro-hole position is decomposed into galvanometer coordinates (large-format coarse positioning) and AOD aperture parameters (micro-hole size and roundness optimization) through the control system 16. The scanning galvanometer 18 is responsible for guiding the beam to the vicinity of the target position, and the one-dimensional AOD 6 is responsible for precisely controlling the aperture and beam rotation. The two work together without interfering with each other, giving full play to the respective advantages of the one-dimensional AOD 6 high-speed micro-hole processing and the scanning galvanometer 18 large-format rapid positioning. This ensures the roundness and processing efficiency of the micro-hole and realizes the batch processing capability of large-size workpieces.

[0060] like Figure 7 As shown, the present invention also provides a laser processing method, comprising the following steps: S1: The control system 16 issues a command to start the rotary motor 9 to drive the Daowei prism 8 to rotate at a preset angular velocity ω (e.g., 30000rpm).

[0061] S2: The original beam output by laser 1 is expanded and collimated by beam expander 2, guided by first reflector 3 and second reflector 4 and polarized by half-wave plate 5, and then incident on one-dimensional AOD 6 at a preset angle (i.e. polarization direction).

[0062] S3: The control system 16 obtains the corresponding driving frequency and frequency change Δf from the table according to the preset target machining aperture, and sends it to the one-dimensional AOD 6; the one-dimensional AOD 6 generates +1 order diffraction light and emits it at a specific diffraction angle, causing the beam to deviate from the center of the optical axis by a certain angle.

[0063] In this step, the driving power adjustment function of the one-dimensional AOD 6 is used to achieve precise control of the processing energy. Specifically, the control system 16 adjusts the radio frequency power intensity input to the one-dimensional AOD 6 in real time according to the processing stage requirements, thereby changing the diffraction efficiency of the +1st order diffracted light (i.e., the output laser power).

[0064] The process includes two modes: a high-power aperture opening mode and a low-power finishing mode. The high-power AOD driving power (diffraction efficiency >80%) is used during the initial micro-aperture stage to rapidly remove material with high energy density, improving processing efficiency. The low-power finishing mode reduces the AOD driving power (diffraction efficiency 10%–30%) when nearing penetration or when improving aperture wall quality, using low energy density for finishing, reducing the heat-affected zone, and improving aperture wall smoothness. The two modes can automatically switch according to a preset timing sequence, achieving an optimized processing strategy of "high-efficiency aperture opening + high-quality finishing."

[0065] Furthermore, the ability of the one-dimensional AOD 6 to continuously change its driving frequency can be used to achieve rotary cutting scanning drilling. Specifically, the control system 16 continuously changes the driving frequency input to the one-dimensional AOD 6 (i.e., continuously changes Δf) according to the preset rotary cutting trajectory, so that the focused spot scans on the sample surface in a spiral or concentric circle trajectory, thereby realizing the processing of large-diameter micro-holes.

[0066] For example, when machining microholes with a diameter of 100 μm, the AOD driving frequency can be linearly increased from the center frequency to the frequency corresponding to a radius of 50 μm, and then linearly decreased back to the center frequency. Combined with the high-speed rotation of the Daowei prism 8, the light spot draws a circular trajectory on the focal plane, achieving rotary cutting and hole enlargement. Using this method, microholes with a diameter much larger than the focused light spot can be machined, with smooth hole walls and high roundness.

[0067] S4: The +1st order diffracted light, which is off the center of the optical axis, is filtered by the slit aperture 7 to remove any unwanted orders and then incident on the high-speed rotating Dowell prism 8; the Dowell prism 8 rotates at an angular velocity ω, and the outgoing beam rotates at a high speed at an angular velocity of 2ω.

[0068] S5: The high-speed rotating beam enters the 4f imaging system and is precisely imaged onto the entrance pupil of the processing focusing lens 13. At the same time, it is scaled according to the F2 / F1 ratio and then enters the processing focusing lens 13.

[0069] S6: The focusing lens 13 for processing focuses the light beam onto the processing surface of the sample 14 to form a micron-scale, time-averaged equivalent circular focal spot.

[0070] In this step, since the Dowell prism 8 rotates at a high speed of ω, the outgoing beam rotates at an angular velocity of 2ω. The elliptical spot that may exist under static conditions is transformed into an ideal circular focal spot (i.e., a true circular focal spot) under the time averaging effect.

[0071] S7: The control system 16 drives the motion platform 15 to move the sample 14 along a preset trajectory (e.g., processing holes one by one in an array). At the same time, the one-dimensional AOD 6 synchronously adjusts the driving frequency and power to process micropores of different diameters and precisions.

[0072] In summary, the laser micromachining system and its processing method of the present invention have the following advantages: 1. By setting up a one-dimensional AOD6 and a Daowei prism 8 for decoupling and collaboration, the one-dimensional AOD6 is only responsible for adjusting the diffraction angle in a single dimension to control the aperture, while the Daowei prism 8 is responsible for the high-speed rotation of the beam to eliminate elliptic aberration. The two functions are independent and do not interfere with each other. Compared with the traditional two-dimensional AOD system, the control dimension is reduced from two dimensions to one dimension. There is no need for complex polarization state adjustment and dual-axis synchronization algorithms, and there is no need to set up complex polarization adjustment and dual-axis synchronization control. This greatly reduces the complexity of the laser micromachining system and the difficulty of software development, and simplifies the structure and makes control easier.

[0073] 2. By setting the high-speed rotation of the Daowei prism 8, the static elliptical spot is transformed into an ideal circular focal spot under time averaging. This directly eliminates the poor roundness of the output beam of the laser 1 and the distortion and astigmatism caused by the adjustment of the beam expander 2, thus eliminating elliptical aberration and making the focused spot an ideal circle, ensuring the true roundness of the micro-hole processing.

[0074] 3. By setting up a one-dimensional aperture 6 and electrically connecting it to the control system 16, and by storing a database of "target aperture - AOD driving frequency" mapping relationships within the control system 16, the control system 16 can calculate the corresponding driving frequency command in real time based on the preset micro-hole processing parameters by looking up a table or calculating the difference. By controlling the driving radio frequency power intensity of the one-dimensional AOD 6, the intensity of the diffracted light can be precisely adjusted, thereby precisely controlling the laser power and single-pulse energy used for processing. This allows for flexible switching between high-power, high-efficiency processing and low-power, precise processing, enabling high-power, high-efficiency hole opening combined with low-power fine finishing, thus comprehensively improving processing efficiency and quality. Moreover, the processed hole diameter has a linear relationship with the change in AOD driving frequency Δf. The hole diameter can be continuously adjusted through simple frequency control, supporting fixed-frequency processing of fixed hole diameters. It can also achieve rotary cutting and scanning drilling through gradual frequency changes. The control is simple and the response speed is fast (microsecond level). Furthermore, due to its extremely high angular resolution and scanning speed, the 1D AOD 6 can achieve high speed, high acceleration, and high precision when machining small holes, making it suitable for micron-level hole machining. Moreover, the single-hole machining time is extremely short. When combined with the motion platform 15, it can achieve large-format, high-efficiency machining, effectively improving machining efficiency.

[0075] 4. By setting the processing focusing lens 13 as a telecentric field lens, true circular micropores with a minimum aperture of 7 μm can be processed. By setting the processing focusing lens 13 as a high-power objective lens, true circular micropores with a minimum aperture of hundreds of nanometers can be processed.

[0076] 5. By setting the first focusing lens 11 and the second focusing lens 12 to form a 4f imaging system, the light field distribution of the exit surface of the Dowell prism 8 is accurately imaged onto the entrance pupil surface of the processing focusing lens 13, effectively eliminating the diffraction effect. Furthermore, the focusing performance is optimized by flexibly selecting the focal length ratio F2 / F1, while filtering out high-frequency noise.

[0077] 6. By adding a scanning galvanometer 18 between the second focusing lens 12 and the processing focusing lens 13, the scanning galvanometer 18 adjusts the processing position of the micro-hole within the field of view of the processing focusing lens 13 by controlling the scanning center, realizing rapid multi-point drilling within a single area. After the processing task within the scanning area of ​​one field lens is completed, the sample 14 is moved to the next processing area by the motion platform 15, and the processing is repeated, realizing high-efficiency, high-speed, and large-format drilling. During the processing, the target micro-hole position is decomposed into galvanometer coordinates and AOD aperture parameters by the control system 16. The scanning galvanometer 18 is responsible for guiding the beam to the vicinity of the target position, and the one-dimensional AOD 6 is responsible for accurately controlling the aperture and beam rotation. The two work together without interfering with each other, giving full play to the respective advantages of the one-dimensional AOD 6 high-speed micro-hole processing and the scanning galvanometer 18 large-format rapid positioning, which not only ensures the roundness and processing efficiency of the micro-hole, but also realizes the batch processing capability of large-size workpieces.

[0078] Any combination of various embodiments of the present invention, provided it does not violate the inventive concept of the present invention, shall be regarded as the content disclosed by the present invention; within the scope of the technical concept of the present invention, any simple modifications to the technical solution and any combination of different embodiments that do not violate the inventive concept of the present invention shall be within the protection scope of the present invention.

Claims

1. A laser micromachining system, characterized in that, include: Laser, control system, beam expander, half-wave plate, one-dimensional AOD, slit stop, Dowell prism, 4f imaging system and focusing lens for processing arranged in sequence along the optical path; The laser is configured to emit a laser beam with a Gaussian intensity distribution; the beam expander is used to expand, collimate, and control the divergence angle of the laser beam output by the laser, so that the diameter of the output beam matches the incident diameter of the one-dimensional AOD. The half-wave plate is used to adjust the polarization direction of the incident light to match the incident conditions of the one-dimensional AOD; the one-dimensional AOD is used to convert the radio frequency driving signal into ultrasonic waves in the crystal, form a Bragg diffraction grating in the crystal, and diffract the incident laser; and the one-dimensional AOD is only used to control the deflection of the beam along a single dimension. The slit stop is used to filter out unwanted diffraction light, allowing only the +1st order diffraction light to enter the Dove prism; The Dowell prism is coaxially mounted at the center of the rotor of a rotary motor; when the rotary motor drives the Dowell prism to rotate at an angular velocity ω, the emitted beam rotates at a high speed around its optical axis at an angular velocity of 2ω. The 4f imaging system is used to image the light field distribution of the exit surface of the Dowell prism onto the entrance pupil surface of the processing focusing lens; the processing focusing lens is used to focus the laser beam, which has been rotated and controlled by the Dowell prism, into a focal spot and apply it to the processing surface of the sample. The control system is electrically connected to the laser, the one-dimensional AOD, and the rotating motor.

2. The laser micromachining system as described in claim 1, characterized in that: The control system has a pre-stored database of "target aperture - AOD driving frequency" mapping relationships.

3. The laser micromachining system as described in claim 1, characterized in that: The 4f imaging system includes a first focusing lens and a second focusing lens, and the first focusing lens, the second focusing lens, and the processing focusing lens are coaxial.

4. The laser micromachining system as described in claim 3, characterized in that: The focal length of the first focusing lens is F1, and the focal length of the second focusing lens is F2; ​​the 4f imaging system images the high-speed rotating beam emitted from the Dowell prism onto the entrance pupil of the processing focusing lens in a ratio of F2 / F1.

5. The laser micromachining system as described in claim 1, characterized in that: It also includes a first reflector and a second reflector arranged along the optical path between the beam expander and the half-wave plate. The first reflector and the second reflector are used to adjust the transmission direction of the laser beam and provide fine-tuning dimension so that the laser beam is incident on the one-dimensional AOD at a preset angle.

6. The laser micromachining system as described in claim 3, characterized in that: It also includes a third reflecting mirror arranged along the optical path between the Dowell prism and the first focusing mirror. The third reflecting mirror is used to adjust the transmission direction of the laser beam and provide fine-tuning dimension so that the laser beam is incident on the first focusing mirror and the second focusing mirror in a direction that coincides with the optical axis of the first focusing mirror and the second focusing mirror.

7. The laser micromachining system as described in claim 3, characterized in that: A fourth reflecting mirror is provided between the first focusing mirror and the second focusing mirror, and the fourth reflecting mirror is used to adjust the direction of beam transmission.

8. The laser micromachining system as described in claim 3, characterized in that: A scanning galvanometer is provided between the second focusing lens and the processing focusing lens. The scanning galvanometer is used to perform rapid and precise scanning control of the light beam within the scanning area of ​​the processing focusing lens, so as to achieve precise positioning of the position to be processed.

9. A laser micromachining method, characterized in that, Using the laser micromachining system as described in any one of claims 1 to 8, Includes the following steps: S1: The control system issues a command to start the high-speed rotating motor to drive the Daowei prism to rotate at a preset angular velocity ω; S2: The original beam output by the laser is expanded and collimated by a beam expander, and after being polarized by a half-wave plate, it is incident on a one-dimensional AOD at a preset angle; S3: The control system sends the corresponding driving frequency and frequency change to the one-dimensional AOD according to the preset target machining aperture; the one-dimensional AOD generates +1 order diffracted light and emits it at a specific diffraction angle, causing the beam to deviate from the center of the optical axis by a certain angle. S4: The +1st order diffracted light, which is off-center from the optical axis, is filtered through a slit aperture until it is filtered out of order and then incident on a high-speed rotating Dowell prism; the Dowell prism rotates at an angular velocity ω, and the outgoing beam rotates at a high speed at an angular velocity of 2ω. S5: The high-speed rotating beam enters the 4f imaging system and is precisely imaged onto the entrance pupil of the focusing lens used for processing. At the same time, it is scaled up by the F2 / F1 ratio and then enters the focusing lens. S6: The focusing lens used in the processing focuses the light beam onto the processing surface of the sample, forming a micron-scale, time-averaged equivalent circular focal spot.

10. The laser micromachining method as described in claim 9, characterized in that, The control system is electrically connected to a motion platform, and the sample is placed on the motion platform. The system also includes the following steps: S7: The control system drives the motion platform to move the sample along a preset trajectory. At the same time, the one-dimensional AOD synchronously adjusts the driving frequency and power to process micropores of different diameters and precisions.

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