A laser beam expansion method, beam expander group, processing equipment, and storage medium

Abstract

The present invention provides a laser beam expansion method, a beam expander group, a processing device, and a storage medium. The method steps include: rotating a first zero-order half-wave plate assembly, injecting randomly polarized laser light, and dividing the light beam into 1 / 2 reflected light a and 1 / 2 transmitted light b; the 1 / 2 reflected light a is reflected by a first thin-film polarizer and a second reflector to a third zero-order half-wave plate assembly to divide the light beam into: 1 / 4 transmitted light e and 1 / 4 reflected light f; the 1 / 4 transmitted light e is transmitted through a third thin-film polarizer; the 1 / 4 reflected light f is reflected out through a third thin-film polarizer and a third reflector; the 1 / 2 transmitted light b passes through the first thin-film polarizer and is incident on a rotating second zero-order half-wave plate assembly to be split into: 1 / 4 transmitted light c, which is transmitted through a second thin-film polarizer, and 1 / 4 reflected light d, which is reflected out through the second thin-film polarizer and a first reflector in sequence. Thus, parallel beam expansion with a large beam expansion ratio can be achieved within a short optical path.

Description

Technical Field

[0001] The present invention relates to laser beam expansion technology, and particularly to a method for expanding a laser beam by multiple polarizations, a beam expander group, a processing device made therefrom, and a storage medium. Background Art

[0002] Laser beam expansion technology is mainly used to expand the diameter of a parallel input beam into a larger parallel output beam. This technology is developed from the basis of an afocal system design, which is developed from an optical telescope, so that the light rays of an object located at infinity enter the optical axis of the internal optical component in a parallel manner and also leave in a parallel manner, and the entire system does not have a focal length. Therefore, this technology is particularly suitable for occasions where it is necessary to adjust the diameter and divergence angle of a laser beam, such as in laser scanning, interferometric measurement, or telemetry applications. Through the design of different beam expansion schemes, the laser system can be made to more flexibly adapt to various application requirements, thereby improving the performance and efficiency of the laser system.

[0003] Currently, for lasers with a small divergence angle, that is, lasers that are infinitely close to perfect collimation, the existing laser beam expansion methods are mainly divided into: transmissive beam expansion, such as Galilean telescope structures and Keplerian telescope structures; reflective beam expansion, such as off-axis reflection and prism multi-pass reflection structures; and grating beam expansion, such as polymer beam splitting DOE.

[0004] However, all of the above existing technical solutions have the problem of beam expansion where a large beam expansion ratio cannot be achieved within a short optical path. In addition, the polymer beam splitting DOE solution also has the disadvantages of low diffraction efficiency and accompanied higher-order diffraction, and the output beam will be deflected, resulting in the problem of dispersing the incident beam into multiple laser beams in different directions. Summary of the Invention

[0005] Therefore, the main object of the present invention is to provide a laser beam expansion method, a beam expander group, a processing device, and a storage medium to achieve parallel beam expansion with a large beam expansion ratio within a short optical path.

[0006] To achieve the above object, according to one aspect of the present invention, there is provided a laser beam expander group, which includes: a first zero-order half-wave plate assembly, a first thin film polarizer, a second zero-order half-wave plate assembly, a second thin film polarizer, a first reflector, a third zero-order half-wave plate assembly, a second reflector, a third reflector, and a third thin film polarizer. The first zero-order half-wave plate assembly is perpendicular to the optical axis and rotates. The first thin film polarizer is disposed on the output optical path of the first zero-order half-wave plate assembly and is disposed at an angle of 45° with the incident optical axis. The first and second thin film polarizers are mirror-image disposed. The second zero-order half-wave plate assembly is disposed between the first and second thin film polarizers and rotates, and is perpendicular to the incident optical axis. The first reflector is disposed on the reflected optical path of the second thin film polarizer and is parallel to each other. The second reflector is disposed on the reflected optical path of the first thin film polarizer and is parallel to each other. The third zero-order half-wave plate assembly is disposed on the reflected optical path of the second reflector and rotates, and is perpendicular to the incident optical axis. The third thin film polarizer is disposed on the output optical path of the third zero-order half-wave plate assembly and is disposed at an angle of 45° with the incident optical axis. The third reflector is disposed on the reflected optical path of the third thin film polarizer and is parallel to each other.

[0007] In a possible preferred embodiment, a parallelogram-like layout form that is mirror-image to each other is formed among the third zero-order half-wave plate, the third reflector, and the third thin film polarizer, and between the second zero-order half-wave plate, the second thin film polarizer, and the first reflector, so that the light beams reflected and transmitted from the third reflector, the third thin film polarizer, the second thin film polarizer, and the first reflector are parallel and the light waists are closely spliced.

[0008] In a possible preferred embodiment, the mirror surface sizes of the third zero-order half-wave plate and the second zero-order half-wave plate are similar; the mirror surface sizes of the first thin film polarizer, the second thin film polarizer, the first reflector, the second reflector, the third reflector, and the third thin film polarizer are similar; the second reflector and the third thin film polarizer are respectively disposed in a right triangle layout form with the third zero-order half-wave plate and the optical axis; the first thin film polarizer and the second thin film polarizer are respectively disposed in a right triangle layout form with the second zero-order half-wave plate and the optical axis.

[0009] In a possible preferred embodiment, the first, second, and third zero-order half-wave plate assemblies respectively include: a zero-order half-wave plate and a rotating device. The zero-order half-wave plate is connected to the rotating end of the rotating device and is axially rotated by the driving of the rotating device.

[0010] In a possible preferred embodiment, the beam expansion ratio of the laser beam expander group is 4.

[0011] To achieve the above object, according to another aspect of the present invention, there is also provided a laser processing device, which includes: a laser, a beam expander system and a focusing system, wherein the beam expander system employs any one of the above-mentioned laser beam expander lens groups.

[0012] To achieve the above object, according to another aspect of the present invention, there is also provided a laser beam expansion method, the steps of which include:

[0013] Rotate the first zero-order half-wave plate assembly, and inject randomly polarized laser light into it. Then, through the first thin-film polarizer, the beam energy is split into two orthogonally linearly polarized light beams: 1 / 2 reflected light a and 1 / 2 transmitted light b.

[0014] The 1 / 2 reflected light a is reflected by the second mirror and then reaches the rotating third zero-order half-wave plate assembly. Then, through the third thin-film polarizer, the beam energy is split into two orthogonally linearly polarized light beams again: 1 / 4 transmitted light e and 1 / 4 reflected light f.

[0015] The 1 / 4 transmitted light e is transmitted from the third thin-film polarizer; the 1 / 4 reflected light f is reflected by the third mirror and is parallel to the 1 / 4 transmitted light e with the optical waists closely spliced.

[0016] The 1 / 2 transmitted light b passes through the first thin-film polarizer and is incident on the rotating second zero-order half-wave plate assembly. Then, through the second thin-film polarizer, the beam energy is split into two orthogonally linearly polarized light beams again: 1 / 4 transmitted light c and 1 / 4 reflected light d.

[0017] The 1 / 4 transmitted light c is transmitted from the second thin-film polarizer and is parallel to the 1 / 4 transmitted light e with the optical waists closely spliced; the 1 / 4 reflected light d is reflected by the first mirror and is parallel to the 1 / 4 transmitted light c with the optical waists closely spliced.

[0018] To achieve the above object, corresponding to the above method, according to another aspect of the present invention, there is also provided a computer-readable storage medium, which stores a computer program, wherein when the computer program is executed, the steps of the above-mentioned laser beam expansion method are realized.

[0019] Through the laser beam expansion method, beam expander lens group, processing device and storage medium provided by the present invention, the optical characteristics of zero-order half-wave plates, thin-film polarizers and mirrors are ingeniously utilized, and a lens combination structure is correspondingly designed. In this way, a 4-fold beam expansion effect can be formed within an extremely short optical path. At the same time, since the transmissive beam expansion method is not adopted and all planar optical elements are used, the beam is not affected by the lens surface and will not generate aberration. The uniformity of the optical power density after beam expansion is high, and the divergence angle of the initial light spot will not be changed. Therefore, the beam quality can be maintained well after beam expansion. Description of the Drawings

[0020] The accompanying drawings, which form a part of this application, are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0021] Figure 1 It is a schematic structural diagram of the laser beam expander group of the present invention;

[0022] Figure 2 It is a schematic diagram of the light beam reflection and transmission routes in the laser beam expander group of the present invention;

[0023] Figure 3 It is a schematic diagram of the axial rotation of the first zero-order half-wave plate assembly in the laser beam expander group of the present invention;

[0024] Figure 4 It is a schematic diagram of the steps of the laser beam expansion method of the present invention.

[0025] Description of reference numerals

[0026] Laser 1, first zero-order half-wave plate assembly 2, first thin film polarizer 3, second zero-order half-wave plate assembly 4, second thin film polarizer 5, first reflector 6, third zero-order half-wave plate assembly 7, second reflector 8, third reflector 9, third thin film polarizer 10, 1 / 2 reflected light a, 1 / 2 transmitted light b, 1 / 4 transmitted light e, 1 / 4 reflected light f, 1 / 4 transmitted light c, 1 / 4 reflected light d. Detailed implementation manners

[0027] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the following will clearly and completely describe the specific technical solutions of the present invention in conjunction with the embodiments, so as to help those skilled in the art further understand the present invention. Obviously, the embodiments described in this case are only a part of the embodiments of the present invention, rather than all the embodiments. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention and without conflict with each other, the embodiments in this application and the features in the embodiments can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of disclosure and protection of the present invention.

[0028] In addition, in the description, claims and drawings of the present invention, terms such as "first", "second", etc. are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the features used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present invention described here can be implemented in an order other than those described here. At the same time, the stages described in each step are not necessarily implemented in the same step. It should be understood that the implementation order of the content in each step stage can be adjusted and interchanged without violating the inventive concept, so that the step embodiments of the present invention described here can be implemented in an order other than those described here. In addition, the terms "comprising" and "having" in the present invention and any variations thereof are intended to cover non-exclusive inclusion. Unless otherwise clearly specified and defined, the terms "arranged", "disposed", "installed", "connected", "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in this case can be understood according to specific circumstances in combination with the prior art.

[0029] In order to achieve parallel beam expansion with a large beam expansion ratio within a short optical path, please refer to Figures 1 to 3 As shown, the present invention provides a laser beam expander group, and its example includes: a first zero-order half-wave plate assembly 2, a first thin-film polarizer 3, a second zero-order half-wave plate assembly 4, a second thin-film polarizer 5, a first mirror 6, a third zero-order half-wave plate assembly 7, a second mirror 8, a third mirror 9, and a third thin-film polarizer 10.

[0030] Among them, as Figures 1 to 2 shown, the first zero-order half-wave plate assembly 2 is arranged perpendicular to the optical axis and continuously rotates. The first thin-film polarizer 3 is arranged on the output optical path of the first zero-order half-wave plate assembly 2 and is set at an angle of 45° with the incident optical axis. The laser 1 emits a randomly polarized laser beam into the first zero-order half-wave plate assembly 2, and then the first thin-film polarizer 3 performs 50:50 energy splitting to form two orthogonally linearly polarized light beams: 1 / 2 reflected light a and 1 / 2 transmitted light b, that is, the 1 / 2 reflected light a is reflected by 90° through the first thin-film polarizer 3, and the 1 / 2 transmitted light b is allowed to transmit through it.

[0031] Among them, the first and second thin-film polarizers 3 and 5 are arranged in a mirror image and are perpendicular to each other. The second zero-order half-wave plate assembly 4 is perpendicular to the incident optical axis and is arranged between the first and second thin-film polarizers 3 and 5 and continuously rotates. Among them, the 1 / 2 transmitted light b passes through the first thin-film polarizer 3 and is incident on the second zero-order half-wave plate assembly 4, and then passes through the second thin-film polarizer 5 and is split into two orthogonally polarized light beams again: 1 / 4 transmitted light c and 1 / 4 reflected light d.

[0032] The first mirror 6 is arranged on the reflection optical path of the second thin-film polarizer 5 and is parallel to it. At this time, the 1 / 4 transmitted light c is transmitted from the second thin-film polarizer 5 to form one path of beam expansion, while the 1 / 4 reflected light d is reflected out in sequence through the second thin-film polarizer 5 and the first mirror 6 to form another path of beam expansion, and the two paths of beam expansion of the 1 / 4 reflected light d and the 1 / 4 transmitted light c are parallel and the beam waists are closely spliced.

[0033] Among them, the second mirror 8 is arranged on the reflection optical path of the first thin-film polarizer 3 and is parallel to it. The third zero-order half-wave plate assembly 7 is perpendicular to the incident optical axis and is arranged on the reflection optical path of the second mirror 8 and continuously rotates. At this time, the 1 / 2 reflected light a reflected from the first thin-film polarizer 3 at 90° will be reflected by the second mirror 8 again at 90° to the third zero-order half-wave plate assembly 7, and then passes through the third thin-film polarizer 10 to split the beam energy into two orthogonally polarized light beams again: 1 / 4 transmitted light e and 1 / 4 reflected light f.

[0034] Among them, the third thin-film polarizer 10 is arranged on the output optical path of the third zero-order half-wave plate assembly 7 and is arranged at an angle of 45° with the incident optical axis, and the third mirror 9 is arranged on the reflection optical path of the third thin-film polarizer 10 and is parallel to it. At this time, the 1 / 4 transmitted light e is transmitted from the third thin-film polarizer 10 to form one path of beam expansion, while the 1 / 4 reflected light f is reflected out in sequence through the third thin-film polarizer 10 and the third mirror 9 to form another path of beam expansion, and the two paths of beam expansion of the 1 / 4 reflected light f and the 1 / 4 transmitted light e are parallel and the beam waists are closely spliced.

[0035] Among them, in this example, the first, second, and third zero-order half-wave plate assemblies 2, 4, and 7 respectively include: a zero-order half-wave plate and a rotating device. The zero-order half-wave plate is connected to the rotating end of the rotating device and is driven by the rotating device. As Figure 3 shown, the zero-order half-wave plate rotates axially. Since the rotatable zero-order half-wave plate assembly is an existing mature product, it will not be elaborated here.

[0036] In addition, in a preferred example, between the third zero-order half-wave plate 7, the third mirror 9, and the third thin-film polarizer 10, and between the second zero-order half-wave plate 4, the second thin-film polarizer 5, and the first mirror 6, they are arranged in a parallelogram-like layout that is mirror-imaged to each other, so that the two expanded beams of the 1 / 4 transmitted light e and the 1 / 4 transmitted light c can be parallel and their optical waists can be closely spliced. Thereby, the beams reflected and transmitted from the third mirror 9, the third thin-film polarizer 10, the second thin-film polarizer 5, and the first mirror 6 can all be parallel and their optical waists can be closely spliced.

[0037] In addition, to ensure that the optical waists of the expanded beams in each path are equal, in a preferred example, the mirror surface sizes of the third zero-order half-wave plate 7 and the second zero-order half-wave plate 4 are similar; the mirror surface sizes of the first thin-film polarizer 3, the second thin-film polarizer 5, the first mirror 6, the second mirror 8, the third mirror 9, and the third thin-film polarizer 10 are similar; the second mirror 8 and the third thin-film polarizer 10 are respectively arranged in a right triangle layout with the third zero-order half-wave plate 7 and the optical axis; the first thin-film polarizer 3 and the second thin-film polarizer 5 are respectively arranged in a right triangle layout with the second zero-order half-wave plate 4 and the optical axis. Thus, through this structural constraint, the optical waists of the expanded beams in each path are made equal.

[0038] With this setting, the laser beam expander group performs three polarization beam splittings, enabling the initial laser to be expanded into four beams with equal power, equal optical waists, and closely spliced within a relatively short optical path, achieving a 4-fold beam expansion effect.

[0039] On the other hand, corresponding to the above example of the laser beam expander group, the present invention also provides a laser processing device, which includes: a laser 1, a beam expansion system, and a focusing system, wherein the beam expansion system uses the laser beam expander group described in the above example.

[0040] On the other hand, corresponding to the above example of the laser beam expander group, as Figure 4 shown, the present invention also provides a laser beam expansion method, and its steps include:

[0041] Rotate the first zero-order half-wave plate assembly 2, and inject randomly polarized laser light into it. Then, through the first thin-film polarizer 3, the beam energy is split into two orthogonally polarized light beams: 1 / 2 reflected light a and 1 / 2 transmitted light b.

[0042] Among them, the 1 / 2 reflected light a is successively reflected by the first thin-film polarizer 3 and the second mirror 8 to the rotating third zero-order half-wave plate assembly 7, and then through the third thin-film polarizer 10, the beam energy is split into two orthogonally polarized light beams again: 1 / 4 transmitted light e and 1 / 4 reflected light f.

[0043] Among them, 1 / 4 of the transmitted light e is transmitted from the third thin-film polarizer 10; 1 / 4 of the reflected light f is reflected by the third thin-film polarizer 10 and the third mirror 9 in sequence, and is parallel to the 1 / 4 transmitted light e with the beam waists closely spliced.

[0044] Among them, 1 / 2 of the transmitted light b passes through the first thin-film polarizer 3 and is incident on the rotating second zero-order half-wave plate assembly 4, and then passes through the second thin-film polarizer 5 to split the beam energy in half again into two orthogonally polarized light beams: 1 / 4 of the transmitted light c and 1 / 4 of the reflected light d.

[0045] Among them, 1 / 4 of the transmitted light c is transmitted from the second thin-film polarizer 5 and is parallel to the 1 / 4 transmitted light e with the beam waists closely spliced; 1 / 4 of the reflected light d is reflected by the second thin-film polarizer 5 and the first mirror 6 in sequence, and is parallel to the 1 / 4 transmitted light c with the beam waists closely spliced.

[0046] On the other hand, corresponding to the above example of the laser beam expansion method, the present invention also provides a computer-readable storage medium storing a computer program, wherein when the computer program is executed, the steps of the laser beam expansion method as described above are implemented.

[0047] In summary, through the laser beam expansion method, beam expander group, processing equipment, and storage medium provided by the present invention, the optical characteristics of the zero-order half-wave plate, thin-film polarizer, and mirror are cleverly utilized, and the lens combination structure is correspondingly designed, so that a 4-fold beam expansion effect can be achieved within an extremely short optical path. At the same time, since the transmissive beam expansion method is not adopted and all planar optical elements are used, the beam is not affected by the lens surface and will not generate aberration. The uniformity of the optical power density after beam expansion is high, and the divergence angle of the initial light spot will not be changed. Therefore, the beam quality can be maintained well after beam expansion.

[0048] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and utilize the present invention well. The present invention is only limited by the claims and their full scope and equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

[0049] Those skilled in the art can understand that, in addition to implementing the systems, devices, units, and their respective modules provided by the present invention in the form of pure computer-readable program code, the method steps can be logically programmed to enable the systems, devices, units, and their respective modules provided by the present invention to be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, embedded microcontrollers, etc. Therefore, the systems, devices, and their respective modules provided by the present invention can be regarded as a kind of hardware component, and the modules included therein for implementing various programs can also be regarded as the structures within the hardware component; the modules for implementing various functions can also be regarded as either software programs for implementing the methods or the structures within the hardware component.

[0050] In addition, all or part of the steps in the methods of the above embodiments can be completed by a program instructing relevant hardware. The program is stored in a storage medium, including several instructions for enabling a single-chip microcomputer, a chip, or a processor to execute all or part of the steps of the methods described in various embodiments of the present application. The aforementioned storage medium includes: various media that can store program codes, such as USB flash drives, mobile hard disks, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical discs.

[0051] In addition, any combination can be made among various different embodiments of the embodiments of the present invention, as long as it does not violate the idea of the embodiments of the present invention, and it should also be regarded as the content disclosed in the embodiments of the present invention.

Claims

1. A laser beam expander group, comprising: The first zero-order half-wave plate assembly, the first thin-film polarizer, the second zero-order half-wave plate assembly, the second thin-film polarizer, the first mirror, the third zero-order half-wave plate assembly, the second mirror, the third mirror, the third thin-film polarizer, wherein the first zero-order half-wave plate assembly is perpendicular to the optical axis and rotates, the first thin-film polarizer is arranged on the output optical path of the first zero-order half-wave plate assembly and is arranged at an angle of 45° with the incident optical axis; the first and second thin-film polarizers are arranged in a mirror image; the second zero-order half-wave plate assembly is arranged between the first and second thin-film polarizers and rotates and is perpendicular to the incident optical axis; the first mirror is arranged on the reflected optical path of the second thin-film polarizer and is parallel to it; the second mirror is arranged on the reflected optical path of the first thin-film polarizer and is parallel to it; the third zero-order half-wave plate assembly is arranged on the reflected optical path of the second mirror and rotates and is perpendicular to the incident optical axis; the third thin-film polarizer is arranged on the output optical path of the third zero-order half-wave plate assembly and is arranged at an angle of 45° with the incident optical axis; the third mirror is arranged on the reflected optical path of the third thin-film polarizer and is parallel to it; Among them, between the third zero-order half-wave plate, the third mirror, and the third thin-film polarizer, and between the second zero-order half-wave plate, the second thin-film polarizer, and the first mirror, they are arranged in a parallelogram-like layout in a mirror image of each other, so that the light beams reflected and transmitted from the third mirror, the third thin-film polarizer, the second thin-film polarizer, and the first mirror are parallel and the light waists are closely spliced; among them, the mirror surface sizes of the third zero-order half-wave plate and the second zero-order half-wave plate are similar; the mirror surface sizes of the first thin-film polarizer, the second thin-film polarizer, the first mirror, the second mirror, the third mirror, and the third thin-film polarizer are similar; the second mirror and the third thin-film polarizer are respectively arranged in a right triangle layout with the third zero-order half-wave plate and the optical axis; the first thin-film polarizer and the second thin-film polarizer are respectively arranged in a right triangle layout with the second zero-order half-wave plate and the optical axis.

2. The laser beam expander lens group according to claim 1, wherein the first, second, and third zero-order half-wave plate assemblies respectively comprise: Zero-order half-wave plate, rotating device, the zero-order half-wave plate is connected to the rotating end of the rotating device and is axially rotated by the drive of the rotating device.

3. The laser beam expander group according to claim 1, wherein the beam expansion ratio of the laser beam expander group is 4.

4. A laser processing device, comprising: Laser, beam expansion system and focusing system, wherein the beam expansion system uses the laser beam expander group according to any one of claims 1 to 3.

5. A laser beam expansion method for the laser beam expander group according to any one of claims 1 to 3, the steps of which include: Rotating the first zero-order half-wave plate assembly and injecting randomly polarized laser light into it, and then passing it through the first thin-film polarizer to split the beam energy into two orthogonal linearly polarized light beams: 1 / 2 reflected light a, 1 / 2 transmitted light b; 1 / 2 reflected light a is reflected by the second mirror to the rotating third zero-order half-wave plate assembly, and then passes through the third thin-film polarizer to split the beam energy into two orthogonal linearly polarized light beams again: 1 / 4 transmitted light e, 1 / 4 reflected light f; The 1 / 4 transmitted light e is transmitted from the third thin-film polarizer; the 1 / 4 reflected light f is reflected by the third mirror and is parallel to the 1 / 4 transmitted light e with the optical waists closely spliced. The 1 / 2 transmitted light b passes through the first thin-film polarizer and is incident on the rotating second zero-order half-wave plate assembly, and then passes through the second thin-film polarizer to split the beam energy in half again into two orthogonally polarized light beams: the 1 / 4 transmitted light c and the 1 / 4 reflected light d. The 1 / 4 transmitted light c is transmitted from the second thin-film polarizer and is parallel to the 1 / 4 transmitted light e with the optical waists closely spliced; the 1 / 4 reflected light d is reflected by the first mirror and is parallel to the 1 / 4 transmitted light c with the optical waists closely spliced.

6. A computer-readable storage medium storing a computer program, wherein when the computer program is executed, the steps of the laser beam expansion method as claimed in claim 5 are implemented.

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