A laser dicing apparatus and method

Abstract

This invention relates to the field of laser processing technology, and more particularly to a laser slicing apparatus and method. The laser slicing apparatus includes a laser emitting unit, a time-domain control unit, a scanning and focusing unit, and a workpiece stage arranged sequentially along the optical path. The laser emitting unit outputs an initial single pulse; the pulse splitting component in the time-domain control unit converts the single pulse into a first pulse train with equal energy and intervals; subsequently, the interval adjustment component reassembles the first pulse train into a second pulse train adaptable to non-uniform interval distributions; the scanning and focusing unit precisely focuses the second pulse train to the target depth to scan and form a modified layer. This invention utilizes a dual-coordinated optical path design of a birefringent crystal and an adjustable reflector to solve problems such as uneven energy deposition and thermal defects caused by nonlinear effects during deep slicing, achieving high-quality, high-yield, and efficient cutting and peeling of hard and brittle crystals.

Description

Technical Field

[0001] This invention relates to the field of laser processing technology, and more particularly to a laser slicing apparatus and method. Background Technology

[0002] Laser slicing technology is widely used in semiconductor wafer manufacturing and the processing of hard and brittle materials such as silicon carbide and gallium nitride. This technology uses a laser beam focused inside a crystal ingot to create a localized modified layer at the focal point through nonlinear effects such as multiphoton ionization. The wafer is then peeled off from the ingot along this modified layer.

[0003] Currently, common laser slicing equipment typically employs laser emitters with fixed pulse output modes for scanning. However, in actual slicing, due to differences in material properties at different depths within the ingot, the conditions for the application of nonlinear effects change with the processing depth. Relying solely on fixed single pulses or evenly spaced pulse trains evenly distributed in the time domain often makes it difficult to flexibly match the carrier lifetime and nonlinear absorption characteristics of different materials. This can easily lead to excessive energy deposition at shallower depths, causing thermal damage or microcracks, while insufficient energy deposition at deeper depths results in discontinuous modified layers. This poor processing adaptability severely affects the flatness of the wafer stripping and the yield of the finished product, and requires frequent changes to process parameters, reducing production efficiency. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to solve at least one of the technical problems mentioned above.

[0005] The solution to the technical problem of this invention is: a laser slicing device, comprising a laser emitting unit, a time-domain control unit, a scanning and focusing unit, and a workpiece stage arranged sequentially along the optical path. The laser emitting unit is used to output a single laser pulse. The time-domain control unit includes a pulse beam splitting component and an interval adjustment component arranged sequentially along the optical path. The pulse beam splitting component is used to convert the single laser pulse into a first pulse train in which each sub-pulse has equal energy and equal time interval. The interval adjustment component is used to receive the first pulse train and adjust the time interval between each sub-pulse in the first pulse train to obtain a second pulse train, which is then output to the scanning and focusing unit. The workpiece stage is used to load a crystal ingot. The scanning and focusing unit is used to focus the second pulse train to a target processing depth inside the crystal ingot and to scan and form a modified layer on the plane of the target processing depth.

[0006] As a further improvement to the above technical solution, the pulse beam splitting assembly includes a birefringent crystal array and a half-wave plate arranged sequentially along the optical path. The birefringent crystal array includes a frame and multiple crystal bodies. The frame is provided with multiple parallel positioning slots that extend in a direction perpendicular to the optical path, allowing the crystal bodies to be inserted into or removed from the optical path of the birefringent crystal array along the positioning slots to adjust the number of sub-pulses in the first pulse train. The initial time interval between each sub-pulse in the first pulse train output after passing through the pulse beam splitting assembly can be adjusted by replacing crystal bodies of different thicknesses. The optical axis of each crystal body is parallel to the surface of the crystal body. In two adjacent crystal bodies, the optical axis of the latter crystal body along the optical path is rotated 45° relative to the optical axis of the former crystal body in a plane perpendicular to the optical path. The thickness of the latter crystal body is half the thickness of the former crystal body. The half-wave plate is used to adjust the polarization state of the first pulse train to meet the polarization state requirements of the incident light of the interval adjustment assembly.

[0007] As a further improvement to the above technical solution, the interval adjustment component includes a polarizing beam splitter. The polarizing beam splitter is used to split the first pulse train into a transmission pulse train and a reflection pulse train with orthogonal polarization states to form a transmission optical path and a reflection optical path. The interval adjustment component also includes a first adjustable mirror group and a second adjustable mirror group respectively disposed on the transmission optical path and the reflection optical path of the polarizing beam splitter. The first adjustable mirror group and the second adjustable mirror group are used to adjust the optical path difference between the transmission pulse train and the reflection pulse train. The polarizing beam splitter is also used to receive the transmission pulse train and the reflection pulse train reflected back by the first adjustable mirror group and the second adjustable mirror group along the original path, and to coaxially combine the two at the output port of the polarizing beam splitter to output as the second pulse train.

[0008] As a further improvement to the above technical solution, the first adjustable reflector group includes a first quarter-wave plate, a first reflector, and a first linear drive mechanism disposed on the transmission light path. The first quarter-wave plate is disposed between the transmission light exit surface of the polarizing beam splitter and the first reflector. The first reflector is driven to the first linear drive mechanism, which drives the first reflector to make a linear displacement along the propagation direction of the transmission pulse train. The second adjustable reflector group includes a second quarter-wave plate, a second reflector, and a second linear drive mechanism disposed on the reflection light path. The second quarter-wave plate is disposed between the reflection light exit surface of the polarizing beam splitter and the second reflector. The second reflector is driven to the second linear drive mechanism, which drives the second reflector to make a linear displacement along the propagation direction of the reflection pulse train.

[0009] As a further improvement to the above technical solution, the scanning focusing unit includes a third reflecting mirror, a beam deflection device, and a field mirror arranged sequentially along the optical path. The third reflecting mirror is used to receive the second pulse train and input the second pulse train into the beam deflection device. The field mirror is used to focus the second pulse train inside the crystal ingot. The beam deflection device is used to drive the focused spot of the second pulse train to perform two-dimensional scanning inside the crystal ingot.

[0010] As a further improvement to the above technical solution, the laser emitting unit includes a femtosecond laser, an electric energy attenuator, and an electric beam expander arranged sequentially along the optical path. The electric energy attenuator is used to adjust the single pulse energy entering the time-domain control unit, and the electric beam expander is used to adjust the size of the focused spot finally output by the scanning focusing unit.

[0011] As a further improvement to the above technical solution, the laser slicing device also includes a host computer, which is connected to the laser emitting unit, the time-domain control unit, the scanning and focusing unit and the workpiece stage. The host computer is used to coordinate the control of each unit to match the slicing process parameters, which include the sub-pulse interval, the number of sub-pulses, the sub-pulse energy, the focused spot size and the scanning speed of the second pulse train.

[0012] A laser slicing method using the aforementioned laser slicing apparatus includes: S1. emitting a single laser pulse through a laser emitting unit; S2. converting the single laser pulse output by the laser emitting unit into a first pulse train having a preset number of sub-pulses and a preset initial time interval between the sub-pulses by adjusting the pulse beam splitting component; S3. converting the first pulse train into a second pulse train having a preset time interval between the sub-pulses by adjusting the interval adjustment component; S4. focusing the second pulse train to a target processing depth inside the ingot through the scanning focusing unit and performing a two-dimensional scan to form a modified layer.

[0013] As a further improvement to the above technical solution, in step S2, the pulse beam splitting component includes a birefringent crystal array and a half-wave plate arranged sequentially along the optical path. The half-wave plate is used to adjust the polarization state of the first pulse train to meet the polarization state requirements of the incident light of the interval adjustment component. The birefringent crystal array includes a frame and multiple crystal bodies. The frame is provided with multiple parallel positioning slots. The positioning slots allow the crystal bodies to be inserted into or removed from the optical path of the birefringent crystal array along the positioning slots. When it is necessary to adjust the number of sub-pulses in the first pulse train, the crystal bodies are added or removed from the birefringent crystal array through the positioning slots, so that the number of crystal bodies is N, to generate 2 NN is an integer greater than or equal to 1. When it is necessary to adjust the initial time interval between each sub-pulse in the first pulse train, one or more pairs of crystal bodies in the birefringent crystal array are replaced to achieve proportional adjustment of the initial time interval, and the half-wave plate is rotated synchronously to compensate for the polarization state shift of the first pulse train, so that it continuously meets the polarization state requirements of the incident light of the interval adjustment component.

[0014] As a further improvement to the above technical solution, in step S3, the interval adjustment component includes a polarizing beam splitter. The polarizing beam splitter is used to split the first pulse train into a transmission pulse train and a reflection pulse train with orthogonal polarization states to form a transmission optical path and a reflection optical path. The interval adjustment component also includes a first adjustable mirror group and a second adjustable mirror group respectively disposed on the transmission optical path and the reflection optical path of the polarizing beam splitter. The polarizing beam splitter is also used to receive the transmission pulse train and the reflection pulse train reflected back by the first adjustable mirror group and the second adjustable mirror group along the original path, and to coaxially combine the two at the output port of the polarizing beam splitter to output as the second pulse train. The first adjustable mirror group includes a first quarter-wave plate, a first mirror, and a first linear drive mechanism disposed on the transmission optical path. A quarter-wave plate is disposed between the transmission light exit surface of the polarizing beam splitter and the first reflector. The first linear drive mechanism is used to drive the first reflector to linearly displace. The second adjustable reflector group includes a second quarter-wave plate, a second reflector, and a second linear drive mechanism disposed on the reflected light path. The second quarter-wave plate is disposed between the reflected light exit surface of the polarizing beam splitter and the second reflector. The second linear drive mechanism is used to drive the second reflector to linearly displace. By adjusting the movement distance of the first reflector and the second reflector towards or away from the polarizing beam splitter through the first linear drive mechanism and the second linear drive mechanism, the optical path difference between the transmission pulse train and the reflection pulse train is changed, thereby adjusting the time interval between each sub-pulse in the second pulse train after beam combining.

[0015] The beneficial effects of this invention are as follows: the laser emitting unit outputs an initial single-pulse light source; the time-domain control unit coarsely adjusts the pulse beam splitter and converts the single pulse into a first pulse train with equal energy and equal intervals, and then uses the interval adjustment component to adjust its time distribution to output a second pulse train; the scanning and focusing unit is responsible for guiding the shaped pulse sequence into the target depth of the ingot for two-dimensional scanning; and the workpiece stage provides stable support. Through the synergy of pulse beam splitting and interval adjustment components, pulse sequences with equal or non-equal intervals can be freely constructed according to a specific processing depth, forming a modified layer internally. This solves the problem of uneven energy deposition caused by nonlinear effects at different depths, suppresses thermal accumulation defects and topping phenomena, and ensures the smoothness and continuity of the modified layer as the subsequent peeling interface, thereby improving the flexibility of the slicing process, product yield, and mass production efficiency. This invention also proposes a laser slicing method. Using the above-mentioned laser slicing device, the optimal pulse time sequence can be customized for different depths to achieve uniform modification at different depths. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of a laser slicing device according to one embodiment of the present invention.

[0017] Figure 2 This is a schematic diagram of the structure of a time-domain control unit according to one embodiment of the present invention.

[0018] Figure 3 This is a schematic diagram illustrating the working principle of a pulse beam splitter assembly according to one embodiment of the present invention.

[0019] Figure 4 This is a schematic diagram of the time interval adjustment of the second pulse train according to one embodiment of the present invention.

[0020] The reference numerals in the attached figures are as follows: 1-Femtosecond laser, 2-Laser adjustment device, 3-Time domain control unit, 31-Birefringent crystal array, 311-First crystal body, 312-Second crystal body, 313-Third crystal body, 32-Mirror frame, 33-Half-wave plate, 34-Polarizing beam splitter, 35-Second quarter-wave plate, 36-Second reflecting mirror, 37-First quarter-wave plate, 38-First reflecting mirror, 4-Scanning focusing unit, 42-Third reflecting mirror, 43-Beam deflection device, 44-Field mirror, 5-Crystal ingot, 6-Workpiece stage, 7-Host computer. Detailed Implementation

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments have been briefly explained above. Obviously, the described drawings are only a part of the embodiments of the present invention, and not all of them. Those skilled in the art can obtain other design schemes and drawings based on these drawings without creative effort.

[0022] The following will clearly and completely describe the concept, specific structure, and technical effects of the present invention in conjunction with embodiments and accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention. Furthermore, all connections / linkages mentioned herein do not simply refer to direct connection of components, but rather to the ability to form a better connection structure by adding or reducing connecting accessories according to specific implementation conditions. The various technical features in this invention can be combined interactively without contradicting each other.

[0023] In the laser slicing process of hard and brittle materials, a single fixed pulse mode cannot adapt to the nonlinear absorption characteristics of the material that change drastically with depth, which can easily cause damage to the modified layer.

[0024] Therefore, the present invention proposes a laser slicing device, referring to... Figures 1-4 It includes a laser emitting unit, a time-domain control unit 3, a scanning and focusing unit 4, and a workpiece stage 6 arranged sequentially along the optical path. The laser emitting unit is used to output a single laser pulse. The time-domain control unit 3 includes a pulse beam splitting component and an interval adjustment component arranged sequentially along the optical path. The pulse beam splitting component is used to convert the single laser pulse into a first pulse train in which each sub-pulse has equal energy and equal time interval. The interval adjustment component is used to receive the first pulse train and adjust the time interval between each sub-pulse in the first pulse train to obtain a second pulse train, which is then output to the scanning and focusing unit 4. The workpiece stage 6 is used to load an ingot 5. The scanning and focusing unit 4 is used to focus the second pulse train to the target processing depth inside the ingot 5 and to scan the plane at the target processing depth to form a modified layer.

[0025] The laser emitting unit outputs an initial single-pulse light source; the time-domain control unit 3 coarsely adjusts the pulse beam splitter component and converts the single pulse into a first pulse train with equal energy and equal intervals, and then uses the interval adjustment component to adjust its time distribution to output a second pulse train; the scanning and focusing unit 4 is responsible for guiding the shaped pulse sequence into the target depth of the ingot 5 for two-dimensional scanning; the workpiece stage 6 provides stable support. Through the synergy of the pulse beam splitter and the interval adjustment component, pulse sequences with equal or non-equal intervals can be freely constructed according to a specific processing depth, forming a modified layer inside, solving the problem of uneven energy deposition caused by nonlinear effects at different depths, suppressing thermal accumulation defects and topping phenomena, ensuring the smoothness and continuity of the modified layer as the subsequent peeling interface, and improving the flexibility of the slicing process, product yield, and mass production efficiency.

[0026] The workflow is as follows: First, the ingot 5 to be processed is stably loaded and fixed on the workpiece stage 6; then, the laser emission unit is activated to output an initial single laser pulse; this pulse enters the time domain control unit 3, and is first decomposed by the pulse beam splitting component into a first pulse train with an initial predetermined number and equal time intervals, and then enters the interval adjustment component to rearrange the time axis, generating a second pulse train with equal or non-equal interval characteristics; subsequently, the second pulse train enters the scanning and focusing unit 4, and is precisely positioned at the preset target processing depth under the Z-axis focusing action. The target processing depth refers to the distance from the upper surface of the ingot 5 to the focusing plane; finally, according to the set scanning trajectory, the second pulse train forms a modified layer inside the ingot 5 through multi-photon ionization, avalanche ionization, carrier recombination, thermal diffusion and phase transition and other multi-physical coupling effects. This modified layer serves as the interface for subsequent wafer separation, preparing the boundary layer for the final wafer separation.

[0027] The existing pulse generation method is fixed, making it difficult to flexibly change the number of sub-pulses and the initial time interval according to the nonlinear absorption characteristics of different materials, resulting in poor processing adaptability of the equipment. Therefore, in one embodiment, the pulse beam splitting assembly includes a birefringent crystal array 31 and a half-wave plate 33 arranged sequentially along the optical path direction. The birefringent crystal array 31 includes a frame 32 and multiple crystal bodies. The frame 32 is provided with multiple parallel positioning slots that extend in a direction perpendicular to the optical path, allowing the crystal bodies to be inserted into or removed from the optical path of the birefringent crystal array 31 along the positioning slots to adjust the number of sub-pulses in the first pulse train. The initial time interval between each sub-pulse in the first pulse train output after passing through the pulse beam splitting assembly can be adjusted by replacing crystal bodies of different thicknesses. The optical axis of each crystal body is parallel to the surface of the crystal body. In two adjacent crystal bodies, the optical axis of the latter crystal body along the optical path direction is rotated 45° relative to the optical axis of the former crystal body in a plane perpendicular to the optical path direction. The thickness of the latter crystal body is half the thickness of the former crystal body. The half-wave plate 33 is used to adjust the polarization state of the first pulse train to meet the polarization state requirements of the incident light of the interval adjustment assembly.

[0028] like Figure 2 As shown, the crystal body is placed on a frame 32 with multiple positioning slots. The frame 32 has an upper opening design, allowing the crystal body to be inserted or removed along the positioning slots through the upper opening according to actual process requirements. This adjusts the number of sub-pulses in the first pulse train and allows for adjustment of the initial time interval between sub-pulses in the first pulse train output after passing through the pulse beam splitter by replacing crystal bodies of different thicknesses. For example, when two sub-pulses are needed, only one crystal body is used; when four sub-pulses are needed, two crystal bodies are used; when eight sub-pulses are needed, three crystal bodies are used, and so on. Figure 3 Figure a shows a schematic diagram illustrating how a single laser pulse, after passing through a first crystal body 311, a second crystal body 312, and a third crystal body 313, is successively transformed into 2 sub-pulses, 4 sub-pulses, and 8 sub-pulses. If the number of crystal bodies is N, then the number of output sub-pulses is 2. N The basic principle is as follows: when a laser beam passes through a crystal, a single laser pulse decomposes into orthogonally polarized, time-delayed o-photon pulses and e-photon pulses, with a time interval of Δt = |(n e -n o ) d / c|, where n e and n o Let ... e -n o ) d' / c|, and satisfy the relation Δt'=Δt / (2 N -1). When the required time interval is fixed, the number of sub-pulses can be adjusted by inserting or removing one or more crystal bodies in the birefringent crystal array 31. The following explains how to adjust the initial time interval between sub-pulses in the first pulse train: When the number of sub-pulses is fixed, the time interval can be proportionally adjusted by replacing one or more pairs of crystal bodies in the birefringent crystal array 31 with the half-wave plate 33, such as... Figure 3 b and Figure 3 Figure c illustrates the case of replacing a pair of crystal bodies: If the half-wave plate 33 is rotated 22.5° and a crystal body is inserted at the very front of the birefringent crystal array 31, while simultaneously removing a crystal body from the very back of the birefringent crystal array 31, then Δt' increases to twice its original value. If the half-wave plate 33 is rotated 22.5° and a crystal body is removed from the very front of the birefringent crystal array 31, while simultaneously inserting a crystal body from the very back of the birefringent crystal array 31, then Δt' decreases to half its original value. If the number of operations is n pairs of crystal bodies, then Δt' increases or decreases to twice its original value. N Double or (1 / 2) N The half-wave plate 33 is positioned after the birefringent crystal array 31 to adjust the polarization state of the first pulse train for input to the interval adjustment component. After adjustment by the half-wave plate 33, the polarization direction of the first pulse train forms a 45° angle with the beam splitting direction of the polarization beam splitter 34 in the subsequent interval adjustment component, ensuring efficient utilization of light energy and feasibility of subsequent modulation.

[0029] If only equally spaced pulse trains can be generated, localized thermal defects may occur at certain depths due to excessively rapid heat accumulation at single points, and it cannot dynamically cope with nonlinear absorption differences of varying depths. Therefore, in one embodiment, the interval adjustment component includes a polarizing beam splitter 34, which is used to split the first pulse train into a transmission pulse train and a reflection pulse train with orthogonal polarization states to form a transmission optical path and a reflection optical path. The interval adjustment component also includes a first adjustable mirror group and a second adjustable mirror group respectively disposed on the transmission optical path and the reflection optical path of the polarizing beam splitter 34. The first adjustable mirror group and the second adjustable mirror group are used to adjust the optical path difference between the transmission pulse train and the reflection pulse train. The polarizing beam splitter 34 is also used to receive the transmission pulse train and the reflection pulse train reflected back by the first adjustable mirror group and the second adjustable mirror group along the original path, and then coaxially combine the two at the output port of the polarizing beam splitter 34 to output as the second pulse train. By combining polarization beam splitting with independent reflector groups, the coarsely tuned pulse train is split into two for optical path control in physical space, and then combined for output. The beam combining principle is as follows: the polarization beam splitter 34 splits the incident first pulse train into a transmitted pulse train and a reflected pulse train according to their polarization states. After being reflected by the first and second adjustable reflector groups respectively, the two pulses pass through the corresponding quarter-wave plates again. Due to passing through the quarter-wave plates twice, the polarization state of the beams rotates by 90°. When the two pulse trains with interchanged polarization states return to the polarization beam splitter 34 along their original paths: the pulse returning from the original transmitted path is reflected; the pulse returning from the original reflected path is transmitted; the two pulses are coaxially combined at the output port of the polarization beam splitter 34 and output as the second pulse train. This provides stable hardware support for creating complex temporal envelopes and non-equidistant distributions, breaking the bottleneck of the traditional single temporal distribution of pulse trains.

[0030] For laser slicing at different depths, the nonlinear effect gradually intensifies with increasing processing depth. If equally spaced pulse trains with uniform distribution in the time domain are used, it is easy to experience excessive energy deposition at shallow depths and insufficient energy deposition at deep depths, which is not conducive to the efficient manufacturing of wafers of different thicknesses. Therefore, in one embodiment, the first adjustable reflector group includes a first quarter-wave plate 37, a first reflector 38, and a first linear drive mechanism disposed on the transmission light path. The first quarter-wave plate 37 is disposed between the transmission light exit surface of the polarizing beam splitter 34 and the first reflector 38. The first reflector 38 is driven to be connected to the first linear drive mechanism, which drives the first reflector 38 to make a linear displacement along the propagation direction of the transmission pulse train. The second adjustable reflector group includes a second quarter-wave plate 35, a second reflector 36, and a second linear drive mechanism disposed on the reflection light path. The second quarter-wave plate 35 is disposed between the reflection light exit surface of the polarizing beam splitter 34 and the second reflector 36. The second reflector 36 is driven to be connected to the second linear drive mechanism, which drives the second reflector 36 to make a linear displacement along the propagation direction of the reflection pulse train.

[0031] Both the first and second linear drive mechanisms include a motion platform and a linear motor. The first reflector 38 and the second reflector 36 are fixedly mounted on their respective motion platforms. The transmitted and reflected pulse trains are converted into left- or right-hand circularly polarized light after passing through the first quarter-wave plate 37 and the second quarter-wave plate 35, respectively. After being reflected by the first reflector 38 and the second reflector 36, they pass through the corresponding quarter-wave plates again, rotating their polarization state by 90°, converting into pulse trains perpendicular to and orthogonal to the original polarization state. Finally, they are combined by the polarizing beam splitter 34 to output as the second pulse train. Figure 4 a and Figure 4As shown in Figure b, taking the second pulse train containing two transmission sub-pulse beams and two reflection sub-pulse beams as an example, the pulse train after beam combining presents an alternating arrangement of transmission-reflection-transmission-reflection. When the first reflecting mirror 38 and the second reflecting mirror 36 move to the zero optical path position, the time interval of the sub-pulses in the second pulse train output by beam combining is equal, which is Δt'. The total time scale of the pulse train between the first transmission sub-pulse beam located on the rightmost side and the second reflection sub-pulse beam located on the leftmost side is 3Δt'. When the first reflector 38 or the second reflector 36 moves a certain distance away from or towards the polarizing beam splitter 34, the sub-pulse intervals in the second pulse train are no longer equal: when the first reflector 38 moves a distance ΔL1 towards the polarizing beam splitter 34, the optical path of the transmitted light path is reduced by 2ΔL1, causing the arrival time of the transmitted sub-pulse to be advanced by Δtt=2ΔL1 / c. Since the pulse sequence is fixed, the time advance Δtt will directly change the interval between adjacent pulses: the interval between the first transmitted sub-pulse beam and the first reflected sub-pulse beam, as well as the interval between the second transmitted sub-pulse beam and the second reflected sub-pulse beam, are both increased to ΔT=Δt'+Δtt=Δt'+2ΔL1 / c, and the interval between the second transmitted sub-pulse beam and the first reflected sub-pulse beam is reduced to ΔT'=Δt'-Δtt=Δt'-2ΔL1 / c. The total time scale of the pulse train between the first transmitted sub-pulse beam and the second reflected sub-pulse beam is 2ΔT+ΔT'=3Δt'+2ΔL1 / c. If the second reflecting mirror 36 subsequently moves a distance ΔL2 away from the polarizing beam splitter 34, the optical path length of the reflected light path increases by 2ΔL2, causing the arrival time of the reflected sub-pulse to be delayed by Δtt'=2ΔL2 / c. Since the pulse sequence is fixed, the time delay Δtt' will directly change the interval between adjacent pulses: the interval between the first transmitted sub-pulse beam and the first reflected sub-pulse beam, as well as the interval between the second transmitted sub-pulse beam and the second reflected sub-pulse beam, both increase to ΔTT=ΔT+Δtt'=ΔT+2ΔL2 / c, and the interval between the second transmitted sub-pulse beam and the first reflected sub-pulse beam decreases to ΔTT'=ΔT'-Δtt'=ΔT'-2ΔL2 / c. The total time scale of the pulse train between the first transmitted sub-pulse beam and the second reflected sub-pulse beam is 2ΔTT+ΔTT'=3Δt'+2ΔL1 / c+2ΔL2 / c. Similarly, if the first reflecting mirror 38 and the second reflecting mirror 36 move in opposite directions, that is, the first reflecting mirror 38 moves ΔL1 away from the polarizing beam splitter 34, thus delaying the arrival time of the transmitted sub-pulse, the total time scale of the pulse train between the first transmitted sub-pulse beam and the second reflected sub-pulse beam is reduced to 3Δt'-2ΔL1 / c; the second reflecting mirror 36 moves ΔL2 towards the polarizing beam splitter 34, thus advancing the arrival time of the reflected sub-pulse, the total time scale of the pulse train between the first transmitted sub-pulse beam and the second reflected sub-pulse beam is reduced to 3Δt'-2ΔL2 / c.The moving distances ΔL1 and ΔL2 of the first reflector 38 and the second reflector 36 can be continuously adjusted in the range of micrometers to centimeters, and their values ​​can be equal or unequal. For laser slicing at different depths, the nonlinear effect gradually increases with the increase of processing depth. If an evenly spaced pulse train with a uniform distribution in the time domain is used, it is easy to have excessive energy deposition at shallow depths and insufficient energy deposition at deep depths, which is not conducive to the efficient manufacturing of wafers of different thicknesses. Non-uniformly spaced pulse trains can be adaptively and finely adjusted according to the working depth: the total pulse train time length is appropriately increased at shallow depths to avoid excessive heat accumulation, and the total pulse train time length is appropriately reduced at deep depths to increase the pulse peak power, thereby compensating for nonlinear energy loss, ensuring that the quality of the modified layer is approximately the same at different depths, and avoiding frequent adjustments to subsequent wafer peeling, polishing, and other processes due to depth differences. The first linear drive mechanism and the second linear drive mechanism in this device can drive the first reflector 38 and the second reflector 36 to move in opposite directions, so that the second pulse train forms at least two sub-pulse groups with different time interval characteristics, realizing the output of non-uniformly spaced composite pulse trains, such as... Figure 4 As shown in Figure c, it consists of a preceding pulse train and a following pulse train with time intervals. For materials with a long carrier lifetime, the preceding pulse train induces nonlinear ionization excitation and initial carrier generation at the focal point. Before the initial carriers are fully recombinated, the following pulse train, which arrives after nanoseconds, can efficiently transfer energy to the lattice through free carrier absorption. This effectively suppresses unstable energy deposition caused by excessively rapid energy accumulation in equally spaced pulse trains, avoids the formation of local defects in the modified layer, and improves the wafer peeling quality.

[0032] Uncontrollable factors such as external vibrations or temperature and humidity changes during processing may cause length errors or local energy fluctuations in the scanning trajectory of traditional single-pulse lasers, directly disrupting the continuity of the modified layer. Therefore, in one embodiment, the scanning focusing unit 4 includes a third reflecting mirror 42, a beam deflection device 43, and a field mirror 44 arranged sequentially along the optical path. The third reflecting mirror 42 is used to receive the second pulse train and input it into the beam deflection device 43. The field mirror 44 is used to focus the second pulse train inside the ingot 5. The beam deflection device 43 is used to drive the focused spot of the second pulse train to perform a two-dimensional scan within the ingot 5.

[0033] The beam deflection device 43 is a dual-axis galvanometer or a two-dimensional fast-reflection mirror with Z-axis dynamic focusing function. The relationship between the scanning speed and the parameters of the second pulse train is explained below: Let the scanning speed be v, the laser repetition frequency output by the laser emitting unit be f, and the number of sub-pulses in the second pulse train after time-domain modulation be M=2. NTherefore, for the original laser without time-domain modulation, the number of pulses per unit length is Np = f / v; after time-domain modulation, the number of sub-pulses per unit length increases to Nsp = M. f / v=2 N f / v. If the scanning length error is Δd due to factors such as vibration, temperature and humidity changes during processing, the resulting change in pulse number for the original laser is Δd / Np; while for the pulse train, the change in pulse number is Δd / Nsp, which is only (1 / 2) of the change in the original laser pulse number. N The effect of pulse number variation is significantly reduced or even negligible. Similarly, if the energy fluctuation of a single pulse output by the laser emitting unit is ΔE due to factors such as vibration, temperature and humidity changes during processing, then for the second pulse train, the energy fluctuation of each sub-pulse is only (1 / 2) of ΔE. N The effect of energy change is also significantly reduced or even negligible when the energy level is doubled.

[0034] If the initial energy and spot size of the laser source cannot be dynamically preset according to the material, even with excellent temporal distribution, modification may fail or excessive ablation may occur due to insufficient absolute energy threshold. Therefore, in one embodiment, the laser emitting unit includes a femtosecond laser 1 and a laser adjustment device 2 arranged sequentially along the optical path. The laser adjustment device 2 includes an electric energy attenuator and an electric beam expander. The electric energy attenuator is used to adjust the single-pulse energy entering the temporal control unit 3, and the electric beam expander is used to adjust the final focused spot size output by the scanning focusing unit 4. The electric energy attenuator achieves continuous energy adjustment by rotating a waveplate or inserting a neutral density filter. The electric beam expander adjusts the final focused spot size by changing the beam diameter through adjusting the lens spacing. This dual approach ensures the controllability of the laser energy and spatial size delivered to the temporal control unit 3, improving the equipment's versatility for tasks involving multiple materials and specifications.

[0035] Laser slicing systems involve numerous complex optical components and axis movements. Relying solely on manual trial and error is extremely inefficient and makes it difficult to ensure coordinated parameter matching during dynamic processing. Therefore, in one embodiment, the laser slicing device further includes a host computer 7, which is electrically connected to the laser emitting unit, the time-domain control unit 3, the scanning and focusing unit 4, and the workpiece stage 6. The host computer 7 is used to coordinate the control of each unit to match the slicing process parameters, which include the sub-pulse interval, number of sub-pulses, sub-pulse energy, focused spot size, and scanning speed of the second pulse train.

[0036] The host computer 7 can be an industrial computer or an embedded controller, and is electrically or communicatively connected to the femtosecond laser 1, the electric energy attenuator, and the electric beam expander in the laser emitting unit, the interval adjustment component in the time domain control unit 3, the beam deflection device 43 in the scanning and focusing unit 4, and the displacement stage driver in the workpiece stage 6 via serial port, Ethernet, or a dedicated control card. Based on user-input parameters such as the material type of the ingot 5, the thickness of the ingot 5, and the target slicing depth, the host computer 7 calculates or assists the operator in adjusting the following process parameters: number of sub-pulses, sub-pulse interval, sub-pulse energy, focused spot size, scanning speed, and scanning trajectory spacing, to achieve optimal slicing quality. As an extension, a pick-and-place device for changing the configuration of the birefringent crystal array 31 can also be added, and this pick-and-place device is controlled by the host computer 7.

[0037] Traditional single-pulse or fixed-parameter laser processing methods cannot precisely control the nonlinear effects in deep processing, easily leading to film formation defects, peeling difficulties, or poor yield. To address this, the present invention proposes a laser slicing method using the aforementioned laser slicing device, comprising: S1. emitting a single laser pulse through a laser emitting unit; S2. converting the single laser pulse output by the laser emitting unit into a first pulse train with a preset number of sub-pulses and a preset initial time interval between the sub-pulses by adjusting the pulse beam splitting component; S3. converting the first pulse train into a second pulse train with a preset sub-pulse time interval by adjusting the interval adjustment component; S4. focusing the second pulse train to the target processing depth inside the ingot 5 through the scanning focusing unit 4 and performing a two-dimensional scan to form a modified layer.

[0038] The preset number of sub-pulses, the preset initial time interval of sub-pulses, and the preset time interval of sub-pulses are all determined based on the material properties of the ingot 5 to be processed and the target processing depth. The material properties include at least one parameter of different ingot materials, such as carrier lifetime, nonlinear absorption coefficient, and thermal diffusivity of silicon carbide and gallium nitride. The specific implementation of the two-dimensional scanning includes using either raster scanning or helical scanning as the scanning path. The relationship between scanning speed and the continuity of the modified layer is as follows: the faster the scanning speed, the fewer the number of sub-pulses per unit length, and the lower the continuity of the modified layer; the slower the scanning speed, the greater the heat accumulation. An appropriate scanning speed must be selected based on the material properties to ensure the uniformity and continuity of the modified layer. This method allows for the customization of optimal pulse time sequences for different depths, achieving uniform modification at different depths.

[0039] Traditional optical path reconstruction methods for adjusting the initial configuration of the first pulse train in the process are cumbersome and prone to inaccuracies. Therefore, in one embodiment, in step S2, the pulse beam splitting component includes a birefringent crystal array 31 and a half-wave plate 33 arranged sequentially along the optical path. The half-wave plate 33 is used to adjust the polarization state of the first pulse train to meet the polarization state requirements of the incident light in the interval adjustment component. The birefringent crystal array 31 includes a frame 32 and multiple crystal bodies. The frame 32 has multiple parallel positioning slots for inserting or removing crystal bodies along the optical path of the birefringent crystal array 31. When it is necessary to adjust the number of sub-pulses in the first pulse train, crystal bodies are added or removed from the birefringent crystal array 31 through the positioning slots, so that the number of crystal bodies is N, to generate 2 N N is an integer greater than or equal to 1. When it is necessary to adjust the initial time interval between each sub-pulse in the first pulse train, one or more pairs of crystal bodies in the birefringent crystal array 31 are replaced to achieve proportional adjustment of the initial time interval, and the half-wave plate 33 is rotated synchronously to compensate for the polarization state shift of the first pulse train, so that it continuously meets the polarization state requirements of the incident light of the interval adjustment component.

[0040] Combination Figure 2 and Figure 3 In step a, by physically adding or removing the crystal body in the positioning slot 32 of the frame, the number of sub-pulses can be increased from 2. N to 2 N±1The number of sub-pulses changes. For example, when N=2, there are 4 sub-pulses; adding a crystal body to the birefringent crystal array 31 changes N to 3 and the number of sub-pulses to 8; conversely, removing a crystal body from the birefringent crystal array 31 changes N to 1 and the number of sub-pulses to 2. In actual operation, it is necessary to ensure that the optical axes of adjacent crystal bodies rotate by 45° sequentially and that the thickness of each subsequent crystal body is half that of the previous one. Rotating the half-wave plate 33 by 22.5° can rotate the polarization direction of the first pulse train by 45°, thereby satisfying the polarization state requirements of the interval adjustment component for its incident light. Combined with the replacement of the crystal body in the birefringent crystal array 31, the initial time interval between each sub-pulse in the first pulse train can be scaled. Specifically: When the initial time interval of the first pulse train needs to be increased by 2 times, a crystal body is added to the front end of the birefringent crystal array 31, and a crystal body is removed from the back end of the birefringent crystal array 31, so that the thickness of the last crystal body in the new birefringent crystal array 31 becomes twice that of the last crystal body in the original birefringent crystal array 31. Then, the half-wave plate 33 is rotated 22.5°. When the initial time interval of the first pulse train needs to be reduced by 1 / 2 times, a crystal body is removed from the front end of the birefringent crystal array 31, and a crystal body is added to the back end of the birefringent crystal array 31, so that the thickness of the last crystal body in the new birefringent crystal array 31 becomes 1 / 2 that of the last crystal body in the original birefringent crystal array 31. Then, the half-wave plate 33 is rotated 22.5°. If the initial time interval needs to be scaled by 2... N This process can be repeated n times. The method is logically sound and easy to execute, ensuring lossless adjustment of beam energy.

[0041] If only the generation of basic sub-pulses is achieved, but precise delay combinations ranging from microseconds to nanoseconds cannot be performed in the time domain to address energy loss at different depths, the adverse effects at large depths cannot be eradicated. Therefore, in one embodiment, in step S3, the interval adjustment component includes a polarization beam splitter 34, which splits the first pulse train into a transmission pulse train and a reflection pulse train with orthogonal polarization states to form a transmission optical path and a reflection optical path. The interval adjustment component also includes a first adjustable mirror group and a second adjustable mirror group respectively disposed on the transmission optical path and the reflection optical path of the polarization beam splitter 34. The polarization beam splitter 34 is also used to receive the transmission pulse train and the reflection pulse train reflected back by the first adjustable mirror group and the second adjustable mirror group along the original path, and coaxially combine them at the output port of the polarization beam splitter 34 to output as the second pulse train. The first adjustable mirror group includes a first quarter-wave plate 37, a first mirror 38, and a first linear drive mechanism disposed on the transmission optical path. The first quarter-wave plate 37 is configured to... The first linear drive mechanism is used to drive the first reflector 38 to linearly displace, and the second adjustable reflector group includes a second quarter-wave plate 35, a second reflector 36, and a second linear drive mechanism disposed on the reflected light path. The second quarter-wave plate 35 is disposed between the reflected light exit surface of the polarizing beam splitter 34 and the second reflector 36. The second linear drive mechanism is used to drive the second reflector 36 to linearly displace. The first linear drive mechanism and the second linear drive mechanism respectively adjust the moving distance of the first reflector 38 and the second reflector 36 in the direction away from or towards the polarizing beam splitter 34, thereby changing the optical path difference between the transmitted pulse train and the reflected pulse train, and thus adjusting the time interval between each sub-pulse in the second pulse train after beam combining.

[0042] Let the sub-pulse interval in the first pulse train output by the birefringent crystal array 31 be Δt', the displacement of the first reflector 38 be ΔL1, and the displacement of the second reflector 36 be ΔL2. Then, the relationship between the adjacent sub-pulse intervals of the second pulse train after beam combining is as follows: when ΔL1=ΔL2=0, an equally spaced pulse train is output, with a sub-pulse interval of Δt'. By adjusting the moving distance of any reflector, the optical path of the corresponding optical path can be changed, thereby making the sub-pulse interval in the second pulse train exhibit a non-uniform distribution. Through the above adjustment, the following can be achieved: equally spaced distribution (two reflectors move synchronously at equal distances), non-equal spaced distribution (single reflector moves or two reflectors move at unequal distances), and composite spaced distribution (two reflectors move in opposite directions, generating pulse groups with a large time interval). Among them, in the composite spaced distribution, the time interval between consecutive pulse groups can be independently controlled by the displacement difference of the two reflectors, typically reaching the nanosecond level, which is suitable for material processing with long carrier lifetimes. This method establishes in detail the criteria for time intervention using bidirectional optical path difference: when the displacement of the two sets of mirrors is 0, equally spaced pulses are output; moving the mirror on one side can change the local sub-pulse spacing to create an unequally spaced arrangement; moving the mirror in opposite directions or at unequal distances on both sides can generate a series of pulses with an extremely wide nanosecond span, thus broadening the process adaptability window.

[0043] In summary, the various technical features of this invention do not exist in isolation, but rather form a closely coordinated and synergistic system. The laser emitting unit and beam adjustment assembly provide a stable and highly adjustable basic energy source; the pulse beam splitting assembly achieves efficient coarse adjustment of the pulse quantity and initial time interval, as well as polarization reference setting, through a sophisticated crystal array; the interval adjustment assembly, with its precise dual-path reflector displacement difference, further achieves non-uniform fine adjustment and reorganization of the temporal distribution; finally, under the overall coordination of the system-level computation of the host computer 7, the scanning and focusing unit 4 precisely projects these shaped pulse trains deep into the crystal ingot 5 and performs motion processing. This series of methods, from beam energy, quantity derivation, temporal staggered arrangement to high-precision positioning in three-dimensional space, are progressively in-depth and interconnected, improving the pain points of uneven nonlinear energy accumulation and yield fluctuations caused by environmental interference during deep laser slicing. Unlike conventional superficial improvements that simply increase laser power or change scanning speed, the co-evolutionary path of combining temporal topography customization and spatial precision scanning in this invention enables the device to handle various hard and brittle materials with different band gaps and carrier lifetimes. It also ensures that the quality of the modified layer of ingot 5 remains highly consistent from the shallowest to the deepest layers, ultimately achieving a high material peeling yield and improved mass production efficiency.

[0044] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention, and these equivalent modifications or substitutions are all included within the scope defined by the claims of this application.

Claims

1. A laser slicing device, characterized in that, The device includes a laser emitting unit, a time-domain control unit, a scanning and focusing unit, and a workpiece stage arranged sequentially along the optical path. The laser emitting unit outputs a single laser pulse. The time-domain control unit includes a pulse beam splitting component and an interval adjustment component arranged sequentially along the optical path. The pulse beam splitting component converts the single laser pulse into a first pulse train in which each sub-pulse has equal energy and equal time interval. The interval adjustment component receives the first pulse train and adjusts the time interval between each sub-pulse in the first pulse train to obtain a second pulse train, which is then output to the scanning and focusing unit. The workpiece stage is used to load a crystal ingot. The scanning and focusing unit focuses the second pulse train to the target processing depth inside the crystal ingot and scans the plane at the target processing depth to form a modified layer.

2. The laser slicing device according to claim 1, characterized in that, The pulse beam splitter includes a birefringent crystal array and a half-wave plate arranged sequentially along the optical path. The birefringent crystal array includes a frame and multiple crystal bodies. The frame has multiple parallel positioning slots extending perpendicular to the optical path, allowing the crystal bodies to be inserted into or removed from the optical path of the birefringent crystal array along the positioning slots to adjust the number of sub-pulses in the first pulse train. The initial time interval between each sub-pulse in the first pulse train output after passing through the pulse beam splitter can be adjusted by replacing crystal bodies of different thicknesses. The optical axis of each crystal body is parallel to its surface. In two adjacent crystal bodies, the optical axis of the latter crystal body along the optical path is rotated 45° relative to the optical axis of the former crystal body in a plane perpendicular to the optical path. The thickness of the latter crystal body is half the thickness of the former crystal body. The half-wave plate is used to adjust the polarization state of the first pulse train to meet the polarization state requirements of the incident light of the interval adjustment component.

3. The laser slicing device according to claim 1, characterized in that, The interval adjustment component includes a polarizing beam splitter, which splits the first pulse train into a transmission pulse train and a reflection pulse train with orthogonal polarization states to form a transmission optical path and a reflection optical path. The interval adjustment component also includes a first adjustable mirror group and a second adjustable mirror group respectively disposed on the transmission optical path and the reflection optical path of the polarizing beam splitter. The first adjustable mirror group and the second adjustable mirror group are used to adjust the optical path difference between the transmission pulse train and the reflection pulse train. The polarizing beam splitter is also used to receive the transmission pulse train and the reflection pulse train reflected back by the first adjustable mirror group and the second adjustable mirror group along the original path, and then coaxially combine the two at the output port of the polarizing beam splitter to output as the second pulse train.

4. The laser slicing device according to claim 3, characterized in that, The first adjustable reflector group includes a first quarter-wave plate, a first reflector, and a first linear drive mechanism disposed on the transmission light path. The first quarter-wave plate is disposed between the transmission light exit surface of the polarizing beam splitter and the first reflector. The first reflector is driven to the first linear drive mechanism, which drives the first reflector to make a linear displacement along the propagation direction of the transmission pulse train. The second adjustable reflector group includes a second quarter-wave plate, a second reflector, and a second linear drive mechanism disposed on the reflection light path. The second quarter-wave plate is disposed between the reflection light exit surface of the polarizing beam splitter and the second reflector. The second reflector is driven to the second linear drive mechanism, which drives the second reflector to make a linear displacement along the propagation direction of the reflection pulse train.

5. The laser slicing device according to claim 1, characterized in that, The scanning and focusing unit includes a third reflecting mirror, a beam deflection device, and a field mirror arranged sequentially along the optical path. The third reflecting mirror is used to receive the second pulse train and input the second pulse train into the beam deflection device. The field mirror is used to focus the second pulse train inside the crystal ingot. The beam deflection device is used to drive the focused spot of the second pulse train to perform a two-dimensional scan inside the crystal ingot.

6. The laser slicing apparatus according to claim 1, characterized in that, The laser emitting unit includes a femtosecond laser and a laser adjustment device arranged sequentially along the optical path. The laser adjustment device includes an electric energy attenuator and an electric beam expander. The electric energy attenuator is used to adjust the energy of the single pulse entering the time-domain control unit, and the electric beam expander is used to adjust the size of the focused spot finally output by the scanning focusing unit.

7. The laser slicing device according to claim 1, characterized in that, The laser slicing device also includes a host computer, which is connected to the laser emitting unit, the time-domain control unit, the scanning and focusing unit, and the workpiece stage. The host computer is used to coordinate the control of each unit to match the slicing process parameters, which include the sub-pulse interval, the number of sub-pulses, the sub-pulse energy, the focused spot size, and the scanning speed of the second pulse train.

8. A laser slicing method, using the laser slicing apparatus as described in any one of claims 1-7, characterized in that, include: S1. A single laser pulse is emitted through the laser emitting unit; S2. By adjusting the pulse beam splitting component, the single laser pulse output by the laser emitting unit is converted into a first pulse train with a preset number of sub-pulses and a preset initial time interval between the sub-pulses; S3. By adjusting the interval adjustment component, the first pulse train is converted into a second pulse train with a preset sub-pulse time interval; S4. The second pulse train is focused to the target processing depth inside the ingot by the scanning focusing unit, and a two-dimensional scan is performed to form a modified layer.

9. A laser slicing method according to claim 8, characterized in that, In step S2, the pulse splitting assembly comprises a birefringent crystal array and a half-wave plate arranged in sequence along the optical path, the half-wave plate is used to adjust the polarization state of the first pulse train to meet the polarization state requirement of the incident light of the interval adjusting assembly, the birefringent crystal array comprises a mirror frame and a plurality of crystal bodies, the mirror frame is provided with a plurality of parallel arranged positioning grooves, the positioning grooves are used for inserting or removing the crystal bodies along the optical path of the birefringent crystal array, when it is needed to adjust the number of sub-pulses in the first pulse train, the crystal bodies are increased or extracted in the birefringent crystal array through the positioning grooves, so that the number of crystal bodies is N, so as to generate 2 N sub-pulses, wherein N is an integer greater than or equal to 1; when it is needed to adjust the initial time interval between each sub-pulse in the first pulse train, one or more pairs of crystal bodies in the birefringent crystal array are replaced to realize equal proportion adjustment of the initial time interval, and the half-wave plate is synchronously rotated to compensate for the shift of the polarization state of the first pulse train, so that it continues to meet the polarization state requirement of the incident light of the interval adjusting assembly.

10. A laser slicing method according to claim 8, characterized in that, In step S3, the interval adjustment component includes a polarizing beam splitter, which splits the first pulse train into a transmission pulse train and a reflection pulse train with orthogonal polarization states to form a transmission optical path and a reflection optical path. The interval adjustment component also includes a first adjustable mirror group and a second adjustable mirror group respectively disposed on the transmission optical path and the reflection optical path of the polarizing beam splitter. The polarizing beam splitter is further used to receive the transmission pulse train and the reflection pulse train reflected back by the first adjustable mirror group and the second adjustable mirror group along their original paths, and to coaxially combine them at the output port of the polarizing beam splitter to output as the second pulse train. The first adjustable mirror group includes a first quarter-wave plate, a first mirror, and a first linear drive mechanism disposed on the transmission optical path. The first quarter-wave plate is disposed on... Between the transmission light exit surface of the polarizing beam splitter and the first reflector, the first linear drive mechanism is used to drive the first reflector to linear displacement. The second adjustable reflector group includes a second quarter-wave plate, a second reflector, and a second linear drive mechanism disposed on the reflected light path. The second quarter-wave plate is disposed between the reflected light exit surface of the polarizing beam splitter and the second reflector. The second linear drive mechanism is used to drive the second reflector to linear displacement. By adjusting the movement distance of the first reflector and the second reflector in the direction away from or close to the polarizing beam splitter through the first linear drive mechanism and the second linear drive mechanism respectively, the optical path difference between the transmission pulse train and the reflection pulse train is changed, thereby adjusting the time interval between each sub-pulse in the second pulse train after beam combining.

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