Laser micro-hole machining optical system and micro-hole machining method

Abstract

The invention belongs to the field of laser drilling, and relates to a laser micro-hole machining optical system and a micro-hole machining method.The laser micro-hole machining optical system comprises a laser, a beam expander, a parallel plate, a galvanometer, a spectroscope, a focus lens and a rotary wave plate set; the beam expander, the parallel plate, the galvanometer, the spectroscope and the focus lens are sequentially arranged on a light path where emergent light of the laser is located from front to back. The rotary wave plate group is arranged on a light path where emergent light of the laser is located and located at any position between the beam expander and the focus lens. According to the laser micro-hole machining optical system and the micro-hole machining method, the polarization state of the optical system can be achieved and changed, and debugging is convenient.

Description

Technical Field

[0001] The present invention belongs to the field of laser drilling, and relates to a laser micro-hole processing optical system and a micro-hole processing method, and in particular to a laser micro-hole processing optical system containing a three-wave plate capable of emitting circularly polarized light, and a micro-hole processing method based on the optical system. Background Art

[0002] Laser processing is a non-contact processing method with the advantages of high energy density, low thermal impact, and a wide variety of processing materials. It can be used in a variety of industrial scenarios such as laser drilling, cutting, etching, cleaning, and roughening, and has advantages that traditional processing cannot match. Among them, in the field of laser micro-hole processing, lasers with different polarization states have different effects on the shape of the back of the hole. Using circularly polarized light can process micro-holes with higher roundness on the back.

[0003] At present, there are acousto-optic, electro-optic, wave plate and other modulation methods to achieve circularly polarized light emission from laser optical systems. Electro-optic and acousto-optic modulators have the disadvantages of high cost, low laser damage threshold, complex control method, large use space, poor stability, etc. Commonly used wave plate type polarization converters have the advantages of low cost, low insertion loss, high stability, high laser damage threshold, simple control method, etc., and are suitable for high energy density laser light sources and laser processing fields that require high stability and convenient debugging and installation. In the wave plate type polarization converter, only one or two wave plates are used, and the polarization state that can be changed is limited. For laser optical systems with multiple optical elements such as reflectors, galvanometers, beam splitters and parallel plates and with one or more mechanical swing axis movements, it cannot meet the application requirements of circularly polarized light emission. For example, in the invention application with the publication number CN107991785A, the use of a combined double wave plate to achieve polarization state conversion is recorded. The method recorded in this invention application only realizes the situation of converting linear polarized light 1 into linear polarized light 2. As for the method of changing the polarization state by combining three wave plates, such as the document "Two New Methods for Realizing Polarization Converters Using Rotating Wave Plate Groups", the solution for the wave plate angle is based on the Poincare sphere method, which is complex and difficult to understand. This method is only suitable for the case where the polarization state of the input light at the front and rear ends of the wave plate group is known, and the three wave plates need to be placed together without other optical elements in between. Moreover, for complex optical systems with mechanical swing angles, the adjustment angle of the wave plate cannot be obtained according to this derived formula. Summary of the invention

[0004] In order to solve the above technical problems existing in the background technology, the present invention provides a laser micro-hole processing optical system and a micro-hole processing method which can realize and change the polarization state of the optical system and are easy to debug.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A laser micro-hole processing optical system, characterized in that: the laser micro-hole processing optical system comprises a laser, a beam expander, a parallel plate, a galvanometer, a beam splitter, a focusing mirror and a rotating wave plate group; the beam expander, parallel plate, galvanometer, beam splitter and focusing mirror are arranged in sequence from front to back on the optical path of the laser's output light; the rotating wave plate group is arranged on the optical path of the laser's output light and is located at any position between the beam expander and the focusing mirror.

[0007] The laser micro-hole processing optical system also includes a first reflector and a second reflector; the beam expander, the first reflector, the parallel plate, the second reflector, the galvanometer, the beam splitter and the focusing mirror are arranged in sequence from front to back on the optical path of the output light of the laser.

[0008] The rotating wave plate group comprises a half wave plate, a first quarter wave plate and a second quarter wave plate; the half wave plate, the first quarter wave plate and the second quarter wave plate are arranged at any position between the beam expander and the focusing lens.

[0009] The position between the above-mentioned beam expander and the first reflector is position a; the position between the first reflector and the parallel plate is position b; the position between the second reflector and the galvanometer is position c; the position between the beam splitter and the focusing mirror is position d; the half wave plate, the first quarter wave plate and the second quarter wave plate are all set at position a, at position b, at position c or at position d.

[0010] The position between the above-mentioned beam expander and the first reflector is position a; the position between the first reflector and the parallel plate is position b; the position between the second reflector and the galvanometer is position c; the position between the beam splitter and the focusing mirror is position d; any one of the half-wave plate, the first quarter-wave plate and the second quarter-wave plate is randomly and arbitrarily set at position a, position b, position c and position d.

[0011] The parallel plate rotates; the second reflector, galvanometer, beam splitter and focusing mirror can all rotate 360° around the mechanical C axis; the galvanometer, beam splitter and focusing mirror can all swing ±90° around the mechanical B axis.

[0012] A micro-hole processing method based on the laser micro-hole processing optical system as described above, characterized in that the method comprises the following steps:

[0013] 1) Assembling the laser micro-hole processing optical system as described above;

[0014] 2) Adjust the angle of the rotating wave plate group in the laser micro-hole processing optical system;

[0015] 3) Perform micro-hole processing based on the adjusted laser micro-hole processing optical system.

[0016] The adjustment in step 2) above is accomplished using the polarization transfer matrix equation.

[0017] The specific implementation of the above polarization transmission matrix equation is:

[0018] E o =M5·M4·M t2 ·M3·M t1 ·M2·G3·G2·G1·M1·E i

[0019] in:

[0020] E i is the linear polarization light vector emitted by the laser;

[0021] E o is the outgoing polarized light vector of the laser micro-hole processing optical system;

[0022] M1 is the Jones matrix of the first reflector;

[0023] G1, G2 and G3 are the Jones matrices of the three wave plates in the rotating wave plate group;

[0024] M2 is the Jones matrix of the parallel plate;

[0025] M3 is the Jones matrix of the second reflector;

[0026] M4 is the Jones matrix of the galvanometer;

[0027] M5 is the Jones matrix of the spectroscope;

[0028] Mt1 is the transformation matrix of the second reflector caused by the mechanical C-axis rotation;

[0029] Mt2 is the conversion matrix of the galvanometer caused by the mechanical B-axis swing.

[0030] The advantages of the present invention are:

[0031] The present invention provides a laser micro-hole processing optical system and a micro-hole processing method, wherein the laser micro-hole processing optical system comprises a laser, a beam expander, a parallel plate, a galvanometer, a beam splitter, a focusing mirror and a rotating wave plate group; the beam expander, the parallel plate, the galvanometer, the beam splitter and the focusing mirror are arranged in sequence from front to back on the optical path where the output light of the laser is located; the rotating wave plate group is arranged on the optical path where the output light of the laser is located and is located at any position between the beam expander and the focusing mirror. The present invention uses a polarization transmission matrix equation method to solve the adjustment angle of the three-wave plate, and the solution algorithm can be applied to complex laser optical systems including reflection, transmission, polarization and mechanical swing axis; at the same time, the micro-hole processing method provided by the present invention is applicable to the conditions that the three-wave plate is in any position in the optical path, separated or placed in the same position, and the placement order of the three-wave plate; and the method can also be used to solve the polarization matrix of any optical element in the optical path; at the same time, by solving the polarization matrix equation, the functional relationship between the adjustment angle of the mechanical swing axis and the wave plate is obtained, and in actual use, the wave plate angle of any swing angle can be obtained through the functional relationship, which can complete the realization and change of any polarization state of the optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the principle of the laser micro-hole processing optical system provided by the present invention;

[0033] Figure 2 It is a schematic diagram of the conversion relationship between the incident light of the galvanometer and the light vector of the reflector;

[0034] In the figure:

[0035] 1-laser; 2-beam expander; 3-first reflector; 4-rotating wave plate group; 5-parallel plate; 6-second reflector; 7-galvanometer; 8-beam splitter; 9-focusing mirror; 10-processing surface. DETAILED DESCRIPTION

[0036] See also Figure 1 The present invention provides a laser micro-hole processing optical system, comprising a laser 1, a beam expander 2, a parallel plate 5, a galvanometer 7, a beam splitter 8, a focusing mirror 9 and a rotating wave plate group 4; the beam expander 2, the parallel plate 5, the galvanometer 7, the beam splitter 8 and the focusing mirror 9 are arranged in sequence from front to back on the optical path of the output light of the laser 1; the rotating wave plate group 4 is arranged on the optical path of the output light of the laser 1 and is located at any position between the beam expander 2 and the focusing mirror 9.

[0037] In addition, in order to reduce the volume of the laser micro-hole processing optical system provided by the present invention, the laser micro-hole processing optical system provided by the present invention also includes a first reflector 3 and a second reflector 6; the beam expander 2, the first reflector 3, the parallel plate 5, the second reflector 6, the galvanometer 7, the beam splitter 8 and the focusing mirror 9 are arranged in sequence from front to back on the optical path of the output light of the laser 1.

[0038] The rotating wave plate group 4 includes a half wave plate, a first quarter wave plate and a second quarter wave plate; the half wave plate, the first quarter wave plate and the second quarter wave plate are arranged at any position between the beam expander 2 and the focusing mirror 9. The rotating wave plate group 4 for generating circularly polarized light can be respectively located at positions a, b, c, and d of the optical system, and the three wave plates can be placed in the same position or separately. The rotating wave plate group 4 consists of two quarter wave plates and a half wave plate, and the three can be placed in any order. Exemplarily, the position a is between the beam expander 2 and the first reflector 3; the position b is between the first reflector 3 and the parallel plate 5; the position c is between the second reflector 6 and the galvanometer 7; the position d is between the beam splitter 8 and the focusing mirror 9; the half wave plate, the first quarter wave plate and the second quarter wave plate are all arranged at position a, at position b, at position c or at position d.

[0039] For another example, the position between the beam expander 2 and the first reflector 3 is a position a; the position between the first reflector 3 and the parallel plate 5 is b; the position between the second reflector 6 and the galvanometer 7 is c; the position between the beam splitter 8 and the focusing mirror 9 is d; any one of the half wave plate, the first quarter wave plate and the second quarter wave plate is randomly and arbitrarily set at position a, position b, position c and position d.

[0040] For the polarization state debugging principle of the λ / 2+λ / 4+λ / 4 three-wave plate combination, first use the λ / 2 wave plate to transform the incident polarization state 1 into polarization state 2 (the ellipticity angle is the same as 1, but the azimuth angle is different), then the first λ / 4 wave plate transforms polarization state 2 into linear polarized light 3, and the last λ / 4 wave plate converts linear polarized light 3 into the required elliptical polarized light 4. The three wave plate angles can be debugged manually or by combining the electric wave plate with the machine tool swing axis to realize a fully automatic debugging process. Figure 1 The optical system with double pendulum axes shown in the figure can obtain the functional relationship between the wave plate angle and the pendulum axis through the transmission matrix, so the wave plate angle of any pendulum angle can be obtained through the functional relationship.

[0041] The parallel plate rotates; the second reflector, the galvanometer 7, the beam splitter 8 and the focusing mirror 9 can all rotate 360° around the mechanical C axis; the galvanometer 7, the beam splitter 8 and the focusing mirror 9 can all swing ±90° around the mechanical B axis. The laser micro-hole processing optical system provided by the present invention is a relatively complex laser processing system. The laser beam emitted by the laser 1 is reflected by the first reflector 3 set at 45° and enters the parallel plate 5. After being refracted by the parallel plate 5, it is reflected by the second reflector 6 and enters the galvanometer 7. After being reflected by the galvanometer 7, it passes through the beam splitter 8 and enters the focusing mirror 9, and circular hole processing is performed at the focal position of the processing surface 10, wherein the second reflector, the galvanometer 7, the beam splitter 8 and the focusing mirror 9 can all rotate 360° around the mechanical C axis; the galvanometer 7, the beam splitter 8 and the focusing mirror 9 can all swing ±90° around the mechanical B axis.

[0042] The present invention provides a laser micro-hole processing optical system as described above, and also provides a micro-hole processing method based on the optical system, the method comprising the following steps:

[0043] 1) Assemble the laser micro-hole processing optical system as before;

[0044] 2) The angle of the rotating wave plate group 4 in the laser micro-hole processing optical system is adjusted, wherein the adjustment is completed by using the polarization transmission matrix equation. Specifically, the specific implementation method of the polarization transmission matrix equation is:

[0045] E o =M5·M4·M t2 ·M3·M t1 ·M2·G3·G2·G1·M1·E i (1)

[0046] in:

[0047] E i is the linear polarized light vector emitted by laser 1;

[0048] E o is the outgoing polarized light vector of the laser micro-hole processing optical system;

[0049] M1 is the Jones matrix of the first reflector 3;

[0050] G1, G2 and G3 are Jones matrices of three wave plates in the rotating wave plate group 4 respectively;

[0051] M2 is the Jones matrix of parallel plate 5;

[0052] M3 is the Jones matrix of the second reflector 6;

[0053] M4 is the Jones matrix of galvanometer 7;

[0054] M5 is the Jones matrix of beam splitter 8;

[0055] Mt1 is the transformation matrix of the second reflector 6 caused by the mechanical C-axis rotation, and the transformation matrix is ​​obtained by the following formula (7):

[0056] Mt2 is the transformation matrix of the galvanometer mirror 7 caused by the mechanical B-axis swing, and the transformation matrix is ​​obtained by the following formula (7).

[0057] It can be seen from formula (1) that the theoretical polarization state of the output light of the entire system can be obtained by knowing the coating parameters of each lens and the polarization state of the incident light. Similarly, under the condition that the polarization state of the incident and output light and the polarization matrix of the optical device are known, in order to obtain circularly polarized light, the required azimuth angle of the wave plate group can be obtained by inverse deduction from the above formula. That is, by solving the polarization transmission matrix equation, the adjustment angle of the rotating wave plate group 4 can be obtained. Among them, the optical devices such as the beam expander 2 and the focusing lens 9 with approximately normal incidence have little effect on the polarization state of the entire system, which can be ignored in theory.

[0058] 3) Perform micro-hole processing based on the adjusted laser micro-hole processing optical system.

[0059] Combine the following Figure 1 The technical solution provided by the present invention is described in detail.

[0060] See also Figure 1 The present invention provides a laser micro-hole processing optical system, including a laser 1, a reflector, a focusing mirror 9, a parallel plate 5, a galvanometer 7, a beam splitter 8, a mechanical double swing axis (B axis and C axis) and other complex optical systems, which can be used to adjust and change the polarization state through a three-wave plate system. The adjustment angle of the three-wave plate can be obtained by solving the polarization transmission equation (Formula 1).

[0061] The essence of the polarization transmission equation is to represent the polarization light vector, optical elements, etc. using the Jones matrix, and then establish an equation based on the input and output light vectors.

[0062] Among them, the Jones vector expression of the input and output light vector E is

[0063]

[0064] a1, a2, and δ are the amplitude and phase difference of two orthogonal components in a spatial right-angle system, where the amplitude a is a physical quantity that characterizes the magnitude of light energy.

[0065] In actual optical systems, the polarization matrix of input and output light can be directly measured by a polarization state measuring instrument. A general polarimeter can directly measure the azimuth and ellipticity angle of elliptically polarized light (polarized light whose end motion trajectory is an ellipse) under the principal axis system. The amplitude ratio and phase difference parameters related to the polarization matrix can be calculated by the relationship between the four parameters (such as formula 3).

[0066] sin2ε=sin2βsinδ

[0067] tan2ψ=tan2βcosδ (3)

[0068] in:

[0069] ε Ellipticity angle: refers to the angle between the major axis and the minor axis of elliptically polarized light.

[0070] β amplitude ratio angle: refers to the arc tangent of the ratio of the amplitude in the x direction to the amplitude in the y direction.

[0071] δ phase difference: refers to the phase difference between two perpendicular directions of the light vector.

[0072] ψ azimuth: A physical quantity that describes the direction of the polarized light vector. The azimuth of elliptically polarized light refers to the angle between the major axis of the ellipse and the reference axis.

[0073] The Jones matrix expression of reflective and transmissive optical elements is:

[0074]

[0075] Among them: rp, rs are the complex amplitude vectors of the p and s components of the reflected light respectively; tp, ts are the complex amplitude vectors of the p and s components of the transmitted light respectively.

[0076] The Jones matrix expression of the wave plate is:

[0077]

[0078] Where θ is the angle between the fast axis of the wave plate and the x-axis, and δ is the phase difference.

[0079] The Jones matrix of the optical element in the optical system can also be obtained by actual testing. The test optical route consists of a laser, a quarter wave plate, an optical element to be tested, and a polarization state meter. The laser emits a beam of linearly polarized light, which is adjusted to circularly polarized light by a quarter wave plate and enters the optical element to be tested. The polarization state meter tests the polarization state of the outgoing light. The polarization transmission matrix equation of the entire system is:

[0080] E out =M'·E in (6)

[0081] Solving equation (6) can establish numerical equations between the elements of the polarization matrix expansion, and use the Matlab nonlinear solver function fsolve to solve it. It should be noted that equation (6) is a simplified or basic version of equation (1), where M' is M in equation (4). R or M T .

[0082] For Figure 1 For the optical system with mechanical double pendulum axes shown in the figure, the azimuth and pitch angles of the laser beam need to change continuously under different working conditions, that is, the incident plane of the beam needs to change continuously with the mechanical axis BC axis. The incident vibration plane of the beam changes continuously, which will cause the polarization state of the outgoing light to change. This change can be solved by the transformation matrix.

[0083] See also Figure 2 , take the plane x1oy1 perpendicular to the incident surface of the second reflector 6 as the reference plane, and take the P component corresponding to the x1 axis and the S component to the y1 axis. Similarly, take the plane x2oy2 perpendicular to the incident surface of the galvanometer 7 as x2oy2, then x2oy2 rotates relative to x1oy1. Assume that at a certain moment, the incident surface of the second reflector 6 rotates by an angle of α1 relative to the incident surface of the flat plate 5, that is, x2oy2 rotates by an angle of α1 relative to x1oy1. As follows Figure 2 As shown, the reflected light components Es1r and Ep1r under the x1oy1 coordinate are projected to the x2oy2 coordinate and decomposed to obtain the matrix expression

[0084]

[0085] but It is the conversion matrix generated from the second reflecting mirror 6 to the galvanometer mirror 7 due to the change in azimuth.

[0086] Therefore, the polarization matrix of the above light vectors, optical elements and conversion matrix is ​​obtained and substituted into the polarization transmission matrix equation (1). By using the matrix expansion and nonlinear equation solving algorithm, the adjustment angle of the three-wave plate under circularly polarized light conditions can be obtained.

Claims

1. A laser micro-hole processing optical system, characterized in that: The laser micro-hole processing optical system comprises a laser (1), a beam expander (2), a parallel plate (5), a galvanometer (7), a beam splitter (8), a focusing mirror (9) and a rotating wave plate group (4); the beam expander (2), the parallel plate (5), the galvanometer (7), the beam splitter (8) and the focusing mirror (9) are arranged in sequence from front to back on the optical path of the output light of the laser (1); the rotating wave plate group (4) is arranged on the optical path of the output light of the laser (1) and is located at any position between the beam expander (2) and the focusing mirror (9).

2. The laser micro-hole processing optical system according to claim 1, characterized in that: The laser micro-hole processing optical system also includes a first reflector (3) and a second reflector (6); the beam expander (2), the first reflector (3), the parallel plate (5), the second reflector (6), the galvanometer (7), the beam splitter (8) and the focusing mirror (9) are arranged in sequence from front to back on the optical path of the output light of the laser (1).

3. The laser micro-hole processing optical system according to claim 2, characterized in that: The rotating wave plate group (4) comprises a half wave plate, a first quarter wave plate and a second quarter wave plate; the half wave plate, the first quarter wave plate and the second quarter wave plate are arranged at any position between the beam expander (2) and the focusing lens (9).

4. The laser micro-hole processing optical system according to claim 3, characterized in that: Position a is located between the beam expander (2) and the first reflector (3); position b is located between the first reflector (3) and the parallel plate (5); position c is located between the second reflector (6) and the galvanometer (7); position d is located between the beam splitter (8) and the focusing mirror (9); and the half-wave plate, the first quarter-wave plate and the second quarter-wave plate are all arranged at position a, at position b, at position c or at position d.

5. The laser micro-hole processing optical system according to claim 3, characterized in that: The position between the beam expander (2) and the first reflector (3) is position a; the position between the first reflector (3) and the parallel plate (5) is position b; the position between the second reflector (6) and the galvanometer (7) is position c; the position between the beam splitter (8) and the focusing mirror (9) is position d; and any one of the half-wave plate, the first quarter-wave plate and the second quarter-wave plate is randomly and arbitrarily arranged at position a, position b, position c and position d.

6. The laser micro-hole processing optical system according to any one of claims 2 to 5, characterized in that: The parallel plate rotates; the second reflector, the galvanometer (7), the beam splitter (8) and the focusing mirror (9) can all rotate 360° around the mechanical C axis; the galvanometer (7), the beam splitter (8) and the focusing mirror (9) can all swing ±90° around the mechanical B axis.

7. A micro-hole processing method based on the laser micro-hole processing optical system according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: 1) Assembling the laser micro-hole processing optical system according to any one of claims 1 to 6; 2) adjusting the angle of the rotating wave plate group (4) in the laser micro-hole processing optical system; 3) Perform micro-hole processing based on the adjusted laser micro-hole processing optical system.

8. The method according to claim 7, characterized in that: The adjustment in step 2) is accomplished by using the polarization transmission matrix equation.

9. The method according to claim 8, characterized in that: The specific implementation of the polarization transmission matrix equation is: E o =M5·M4·M t2 ·M3·M t1 ·M2·G3·G2·G1·M1·E i in: E i is the linear polarized light vector emitted by the laser (1); E o is the outgoing polarized light vector of the laser micro-hole processing optical system; M1 is the Jones matrix of the first reflector (3); G1, G2 and G3 are the Jones matrices of the three wave plates in the rotating wave plate set (4); M2 is the Jones matrix of the parallel plate (5); M3 is the Jones matrix of the second reflector (6); M4 is the Jones matrix of the galvanometer (7); M5 is the Jones matrix of the beam splitter (8); Mt1 is the transformation matrix of the second reflector (6) caused by the mechanical C-axis rotation; Mt2 is the conversion matrix of the galvanometer (7) caused by the mechanical B-axis swing.

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