Polarized light modulation method and device

Abstract

The invention belongs to the field of laser processing, and relates to a polarized light modulation method and device, and the method comprises the following steps: 1), obtaining the phases of emergent laser in different polarization states; and 2) performing rotation control on the emergent laser according to the phase obtained in the step 1) to obtain different polarized lights. The invention provides the polarized light modulation method and the polarized light modulation device which are high in response speed and can complete high-quality processing.

Description

Technical Field

[0001] The present invention belongs to the field of laser processing and relates to a polarized light modulation method and device, and in particular to a highly dynamically adjustable rotating polarized light modulation method and device. Background Art

[0002] Polarization is a key characteristic parameter of lasers and plays a crucial role in laser processing, directly impacting material processing effectiveness and efficiency. Currently, laser polarization is typically static or slightly dynamic during use—that is, it remains constant or modulates very slowly. This can lead to isotropic variations in processing quality when processing certain complex features, as the polarization cannot keep pace with the machining, scanning trajectory, or topography adjustments.

[0003] For example, patent number 201310254453.2 discloses a method for controlling the polarization state of laser light based on polarization feedback. This method is primarily used to control the polarization state of a laser output. The method comprises a laser, an external cavity feedback system on the left side of the laser, and a polarization state detection system on the right side. The core of this method is to detect the light intensity signal on a photodetector by rotating a half-wave plate, thereby achieving conversion between horizontally polarized light and vertically polarized light. This patent adjusts the polarization state of the laser output light by rotating the half-wave plate, but it can only adjust horizontally or vertically polarized light and cannot output elliptically or circularly polarized light, limiting its applicability.

[0004] For another example, the invention application with application number 202110639367.8 discloses a light polarization state control device and a method for controlling the light polarization state. It is mainly a light polarization state control device, which includes: a detection module, a control circuit module and a polarization control module; the detection module is used to obtain the first polarization state information and the second polarization state information of the target light beam, the first polarization state information is the polarization information of the target light beam before it enters the polarization control module, and the second polarization state information is the polarization information of the target light beam after it exits the polarization control module; the control circuit module is used to determine the target control voltage based on the first polarization state information and the second polarization state information of the target light beam; the polarization control module is used to adjust the polarization state of the target light beam according to the target control voltage. Its purpose is to achieve stable output of the target polarization state. This invention mainly uses the polarization control module to adjust the change of polarized light, which can only achieve the transformation of a simple polarization state, and cannot achieve the modulation of multiple polarization states.

[0005] However, when laser light interacts with materials, its polarization state significantly impacts processing quality and efficiency. The polarization state emitted by a laser is single. To meet specific processing requirements, a polarization modulation module is often added to the optical path to shape the beam into a specific polarization state. Polarization modulation modules include wave plates or wave plate combinations, spatial light modulation and wave plate combinations, and liquid crystal phase modulators. While these polarization modules can shape linearly polarized light into multiple polarizations, they suffer from the same drawbacks: slow response speed and static polarization state. During processing, the polarization state cannot be modulated in real time, following the laser scanning spot at high speed. Summary of the Invention

[0006] In order to solve the above technical problems existing in the background technology, the present invention provides a polarization light modulation method and device with fast response speed and capable of completing high-quality processing.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A polarization light modulation method, comprising the following steps:

[0009] 1) Obtain the phase of the outgoing laser in different polarization states;

[0010] 2) According to the phase obtained in step 1), the outgoing laser is rotated and controlled to obtain light of different polarizations.

[0011] The specific implementation of step 1) above is:

[0012] 1.1) Measure the polarization direction value γ0 of the outgoing laser using a polarimeter;

[0013] 1.2) Place a half-wave plate and a quarter-wave plate in sequence on the optical path of the outgoing laser;

[0014] 1.3) Keep the half-wave plate stationary and adjust the quarter-wave plate to rotate so that the polarization meter shows a linear polarization signal. Record the linear polarization direction γ1.

[0015] 1.4) Adjust the half wave plate rotation -(γ 1- γ0) / 2 while adjusting the quarter wave plate rotation -(γ 1- γ0), making the polarization direction of the polarimeter γ0, and obtaining the linear polarization state corresponding to the initial phase A(X0, Y0), where X0 is the initial position of the half-wave plate and Y0 is the initial position of the quarter-wave plate;

[0016] 1.5) Using the initial phase A corresponding to the linear polarization state obtained in step 1.4), obtain the phase B corresponding to the circular polarization state and the phase C corresponding to the elliptical polarization state.

[0017] The expression of the phase B corresponding to the circular polarization state in step 1.5) above is: B = (X0, Y0 + 45°);

[0018] The expression of the phase C corresponding to the elliptical polarization state in step 1.5) is: C = (X0+, Y0+θ), where θ≠mπ / 4 (m=0, 1, 2...); θ is the angle between the polarization direction of the light beam emitted from the half-wave plate and the fast axis direction of the quarter-wave plate.

[0019] The specific implementation method of the above step 2) is: rotating the half wave plate and the quarter wave plate respectively, so as to cause the outgoing laser to form light of different polarization states respectively, thereby completing polarization light modulation of the outgoing laser.

[0020] The angular velocity of the half-wave plate is w1, and the angular velocity of the quarter-wave plate is w2; w2 = 2×w1.

[0021] A polarization light modulation device formed based on the polarization light modulation method as described above, the polarization light modulation device includes a main control system, a laser, a half wave plate, a quarter wave plate, a beam expander, a beam scanning system, a motion platform and a wave plate rotation drive device; the half wave plate, quarter wave plate, beam expander and beam scanning system are arranged in sequence from front to back on the output light path of the laser; the processing sample is located on the scanning path of the beam scanning system and is placed on the motion platform and moves freely with the motion platform; the wave plate rotation drive device is respectively connected to the half wave plate and the quarter wave plate and drives the half wave plate and the quarter wave plate to rotate at high speed; the main control system is respectively connected to the laser, the wave plate rotation drive device, the beam scanning system and the motion platform.

[0022] The above-mentioned wave plate rotation drive device includes a first motor, a second motor and a drive controller; the drive controller is connected to the first motor and the second motor respectively; the main control system is connected to the drive controller; the first motor is connected to the half wave plate and drives the half wave plate to rotate at high speed; the second motor is connected to the quarter wave plate and drives the quarter wave plate to rotate at high speed.

[0023] The polarization light modulation device further includes a reflecting mirror arranged between the beam expander and the beam scanning system, and a focusing mirror arranged between the beam scanning system and the processed sample.

[0024] A laser processing method based on the aforementioned polarization light modulation device, the laser processing method comprising the following steps:

[0025] 1) Build a polarization light modulation device;

[0026] 2) Select different polarization states of the laser suitable for the workpiece according to the structural characteristics of the workpiece;

[0027] 3) The main control system is used to control the rotation of the half wave plate and the quarter wave plate, so that the laser light emitted from the laser forms different polarization states required in step 2);

[0028] 4) Processing the workpiece accordingly with the different polarization states of the laser light formed in step 3) until the laser processing operation is completed.

[0029] In the above step 2), the structural features of the workpiece to be processed include a porous structure and a non-circular structure; when the structural feature of the workpiece to be processed in the step 2) is a porous structure, the laser used is circularly polarized light; when the structural feature of the workpiece to be processed in the step 2) is a non-circular structure, the laser used is elliptically polarized light.

[0030] The advantages of the present invention are:

[0031] The present invention provides a method and device for modulating polarized light. The method comprises: 1) obtaining the phase of an outgoing laser beam in different polarization states; and 2) rotating and controlling the outgoing laser beam according to the phase obtained in step 1) to produce light of different polarizations. The present invention provides a device for highly dynamic polarization adjustment, capable of achieving arbitrary, high-speed modulation of linearly polarized light, circularly polarized light, or elliptically polarized light with a simple modulation process. Furthermore, the polarization state can be controlled to dynamically and rapidly change with the laser scanning spot, enabling real-time modulation of the polarization state by tracking the laser processing trajectory, thereby enabling high-speed, high-quality laser processing of various material morphologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of the principle of the polarization light modulation method provided by the present invention;

[0033] Figure 2 Schematic diagram of the laser polarization state measurement process used in the present invention;

[0034] Figure 3 Schematic diagram of the initial phase calibration of the polarized light modulation method adopted by the present invention;

[0035] Figure 4 This is a schematic structural diagram of the polarization light modulation device provided by the present invention;

[0036] Figure 5 This is a schematic diagram of the rotation of the linearly polarized laser along the scanning trajectory when making holes based on the polarization light modulation method provided by the present invention;

[0037] Figure 6 This is a schematic diagram of the light motion trajectory when performing triangle laser cutting based on the polarized light modulation method provided by the present invention;

[0038] in:

[0039] 1-half wave plate; 2-quarter wave plate; 3-first motor; 4-second motor; 5-drive controller; 6-beam expander; 7-reflector; 8-beam scanning system; 9-focusing mirror; 10-motion platform; 11-processing sample; 12-laser; 13-main control system. DETAILED DESCRIPTION

[0040] The present invention provides a polarization light modulation method, the core idea of which is to obtain the phase of the outgoing laser in different polarization states and rotate and control the outgoing laser according to the phase to obtain different polarized lights.

[0041] To illustrate the adjustment method provided by the present invention, see Figure 1 , is a schematic diagram of the process of completing the adjustment of the present invention, Figure 1 The laser beam generator comprises a half-wave plate 1, a quarter-wave plate 2, a first motor 3 and a second motor 4 that respectively drive the half-wave plate 1 and the quarter-wave plate 2 to rotate at high speed, and a drive controller 5 that connects the first motor 3 and the second motor 4. During operation, the laser beam first vertically incidents on the half-wave plate 1, and the outgoing beam then vertically incidents on the quarter-wave plate 2. The first motor 3 drives the half-wave plate 1 to rotate at a speed of w1, and the second motor 4 drives the quarter-wave plate 2 to rotate at a speed of w2.

[0042] Specifically, the polarization light modulation method provided by the present invention is:

[0043] 1) Calibrate the initial phase relationship between the laser and the polarization modulation module.

[0044] 1.1) Pass the incident polarized laser through an attenuator to attenuate the power to within the operating power range of the polarimeter. Figure 2 , measure the polarization direction of the laser by a polarimeter and record the polarization direction value γ0;

[0045] 1.2) Return the first motor 3 and the second motor 4 to zero;

[0046] 1.3) Place the polarization control module between the attenuator and the polarimeter, see Figure 3 As shown. Adjust the second motor 4 to rotate the quarter wave plate 2. When a linear polarization signal appears on the polarization measuring instrument, record the linear polarization direction γ1 at this time.

[0047] 1.4) Adjust the first motor 3 to rotate the half wave plate 1 -(γ 1- γ0) / 2, adjust the second motor 4 to rotate the quarter wave plate 2 -(γ 1-γ0), at this time the polarization direction of the polarization meter is γ0, then the fast axis directions of the half wave plate 1 and the quarter wave plate 2 coincide with or are perpendicular, and the fast axis direction of the half wave plate 1 coincides with the polarization direction of the incident laser, and the positions X0 and Y0 of the half wave plate 1 controlled by the first motor 3 and the quarter wave plate 2 controlled by the second motor 4 are recorded respectively as the initial phase A.

[0048] 1.5) The linear polarization state corresponds to the initial phase A of the polarization control module as (X0, Y0); the circular polarization state corresponds to the initial phase B of the polarization control module as (X0, Y0+45°); and the elliptical polarization state corresponds to the initial phase as (X0, Y0+θ), where θ≠mπ / 4 (m=0, 1, 2...).

[0049] 2) Polarization rotation control

[0050] At the initial phase, the first motor 3 and the second motor 4 are allowed to drive the half wave plate 1 and the quarter wave plate 2 to rotate respectively, and the rotation speed satisfies w2=2*w1. Then, the polarization state corresponding to the initial phase will rotate rapidly to complete the adjustment of different polarization states, where w1 is the angular velocity of the half wave plate 1, and w2 is the angular velocity of the quarter wave plate 2.

[0051] Since the incident laser light is linearly polarized, assuming the angle between it and the fast axis of half-wave plate 1 is α1, the beam after passing through half-wave plate 1 is linearly polarized, but the polarization direction is rotated by 2α1 relative to the original polarization direction and is symmetrical about the fast axis. After linearly polarized light enters quarter-wave plate 2, the polarization state of the outgoing light depends on the angle between the linearly polarized light and the fast axis of quarter-wave plate 2: 1) When the angle is 0° or 90°, the polarization state of the outgoing light is linearly polarized, and the direction remains unchanged; 2) When the angle is ±45°, the polarization state of the outgoing light is circularly polarized; 3) At all other angles, the polarization state of the outgoing light is elliptical.

[0052] Based on the above method, the present invention also provides a polarization light modulation device, see Figure 4 The polarization light modulation device includes a half-wave plate 1, a quarter-wave plate 2, a first motor 3, a second motor 4, a drive controller 5, a beam expander 6, a reflector 7, a beam scanning system 8, a focusing mirror 9, a motion platform 10, a processing sample 11, a laser 12, and a main control system 13. The beam expander 6 is used to expand and collimate the laser beam; the beam scanning system 8 is used to control the laser beam to move along a set trajectory; the focusing mirror 9 is used to focus the laser beam to a point for material processing; the laser 12 is used to generate the laser beam; and the main control system 13 is used to control the coordinated movement of the laser, polarization control system, beam scanning system, and motion system.

[0053] Based on the polarization light modulation device, the present invention also provides a laser processing method, which includes the following steps:

[0054] 1) Build a polarization light modulation device;

[0055] 2) selecting different polarization states of the laser light suitable for the workpiece to be processed according to the structural characteristics of the workpiece to be processed; wherein the structural characteristics of the workpiece to be processed include a porous structure and a non-circular structure; when the structural characteristic of the workpiece to be processed in step 2) is a porous structure, the laser light used is circularly polarized light; when the structural characteristic of the workpiece to be processed in step 2) is a non-circular structure, the laser light used is elliptically polarized light.

[0056] 3) The main control system 13 is used to respectively control the rotation of the half wave plate 1 and the quarter wave plate 2, so that the laser light emitted from the laser 12 forms different polarization states required in step 2);

[0057] 4) Processing the workpiece accordingly with the different polarization states of the laser light formed in step 3) until the laser processing operation is completed.

[0058] For example, in order to illustrate the feasibility of the laser processing method provided by the present invention, the following two embodiments are used for illustration:

[0059] Example 1: High-efficiency laser hole making with linearly polarized light rotation

[0060] The polarization state of the light beam emitted from the laser is usually linearly polarized light. When processing circular holes, the material's absorption of laser light is related to polarization, and the absorption rate of P light is greater than the absorption rate of S light. Therefore, there is anisotropy in the efficiency of removing the material, which ultimately causes the back of the hole to be elliptical. In order to solve the problem of processing anisotropy, a quarter-wave plate is usually added to the optical path to convert linearly polarized light into circularly polarized light. Although this solves the problem of anisotropy, the absorption rate of each point on the circle is equivalent to half of the P light and half of the S light, so the processing efficiency is not optimal. In order to increase the material's absorption rate of laser light, thereby improving processing efficiency, the present invention rotates the linearly polarized light so that each point on the circle is P light, thereby improving laser processing efficiency. Figure 5 shown.

[0061] Specifically, when completing laser hole making, the following contents are included:

[0062] 1) The main control system 13 controls the motion platform 10 to carry the processing sample 11 and move it to the processing focus position;

[0063] 2) The main control system 13 drives the controller 5 to control the first motor 3 and the second motor 4 to return the linear polarization state of the half wave plate 1 and the quarter wave plate 2 to zero (the aforementioned X0 and Y0 initial phases);

[0064] 3) The main control system 13 controls the beam scanning system 8 to return to zero;

[0065] 4) After returning to zero, the main control system 13 controls the half-wave plate 1 to rotate at a speed of w1, the quarter-wave plate 2 to rotate at a speed of 2w1, and the beam scanning system 8 to rotate at a speed of 2w1.

[0066] 5) After the half-wave plate 1, quarter-wave plate 2, and beam scanning system 8 have stabilized, the polarization state of the beam will rotate along a circular trajectory as linearly polarized light, and a state stability signal will be output. Upon receiving this signal, the main control system 13 controls the laser 12 to turn on the laser and begin processing. At the same time, after each layer is processed, the main control system 13 controls the focusing mirror 9 to descend a step distance. The step distance is related to the laser power and scanning speed.

[0067] 6) After the laser processing is completed according to the predetermined trajectory, the main control system receives the end signal and first controls the laser to turn off the laser, and at the same time controls the driver 5 and the beam scanning system 8 to stop moving;

[0068] 7) Processing is completed.

[0069] Example 2: High-efficiency laser cutting with elliptically polarized light following trajectory

[0070] When laser cutting samples, the morphology is varied and not necessarily circular. For irregular patterns, rotating polarization is no longer applicable. Figure 6 As shown, when performing triangle laser cutting, in order to ensure good processing efficiency and processing consistency, the polarization direction of the polarized light needs to be always consistent with the direction of movement. Specifically, the specific method of the laser cutting process is:

[0071] 1) The main control system 13 controls the motion platform 10 to carry the processing sample 11 and move it to the processing focus position;

[0072] 2) The main control system 13 drives the controller 5 to control the first motor 3 and the second motor 4 to return the elliptical polarization state of the half wave plate 1 and the quarter wave plate 2 to zero (the aforementioned X0 and Y0+θ initial phases);

[0073] 3) The main control system 13 calculates the phase values (Xab, Yab), (Xbc, Ybc), and (Xca, Yca) corresponding to the three sides ab, bc, and ca of the half-wave plate 1 and the quarter-wave plate 2 respectively according to the motion trajectory topography and the polarization direction corresponding to the initial phase in the machine tool coordinate system;

[0074] 4) When performing ab trajectory processing, the main control system 13 controls the driver 5 to move the half wave plate 1 and the quarter wave plate 2 to Xab and Yab respectively, then the laser 12 turns on the laser, and the scanning control system controls the light beam to move along ab;

[0075] 5) After reaching point b, laser 12 turns off, and main control system 13 controls driver 5 to move half-wave plate 1 and quarter-wave plate 2 to Xbc and Ybc, respectively. Laser 12 turns on, and the scanning control system controls the beam to move along bc.

[0076] 6) After reaching point c, laser 12 turns off, and main control system 13 controls driver 5 to move half-wave plate 1 and quarter-wave plate 2 to Xca and Yca, respectively. Laser 12 turns on, and the scanning control system controls the beam to move along ca.

[0077] 7) After reaching point a, the laser is turned off and the processing is completed.

Claims

1. A polarization light modulation method, characterized in that: The polarization light modulation method comprises the following steps: 1) Obtain the phase of the outgoing laser in different polarization states; 2) According to the phase obtained in step 1), the outgoing laser is rotated and controlled to obtain light of different polarizations.

2. The polarization light modulation method according to claim 1, wherein: The specific implementation of step 1) is: 1.1) Measure the polarization direction value γ0 of the outgoing laser using a polarimeter; 1.2) Place a half-wave plate and a quarter-wave plate in sequence on the optical path of the outgoing laser; 1.3) Keep the half-wave plate stationary and adjust the quarter-wave plate to rotate so that the polarization meter shows a linear polarization signal. Record the linear polarization direction γ1. 1.4) Adjust the half wave plate rotation - (γ 1- γ0) / 2 while adjusting the quarter wave plate rotation -(γ 1- γ0), making the polarization direction of the polarimeter γ0, and obtaining the linear polarization state corresponding to the initial phase A(X0, Y0), where X0 is the initial position of the half-wave plate and Y0 is the initial position of the quarter-wave plate; 1.5) Using the initial phase A corresponding to the linear polarization state obtained in step 1.4), obtain the phase B corresponding to the circular polarization state and the phase C corresponding to the elliptical polarization state.

3. The polarization light modulation method according to claim 2, wherein: The expression of the phase B corresponding to the circular polarization state in step 1.5) is: B=(X0, Y0+45°); The expression of the phase C corresponding to the elliptical polarization state in step 1.5) is: C = (X0, Y0 + θ), where θ ≠ mπ / 4 (m = 0, 1, 2...); θ is the angle between the polarization direction of the light beam emitted from the half-wave plate and the fast axis direction of the quarter-wave plate.

4. The polarization light modulation method according to claim 1, 2 or 3, wherein: The specific implementation method of step 2) is: rotating the half wave plate and the quarter wave plate respectively to cause the outgoing laser to form light of different polarization states respectively, thereby completing polarization light modulation of the outgoing laser.

5. The polarization light modulation method according to claim 4, wherein: The angular velocity of the half-wave plate is w1, and the angular velocity of the quarter-wave plate is w2; w2=2×w1.

6. A polarization light modulation device formed based on the polarization light modulation method according to any one of claims 1 to 5, characterized in that: The polarization light modulation device comprises a main control system (13), a laser (12), a half wave plate (1), a quarter wave plate (2), a beam expander (6), a light beam scanning system (8), a motion platform (10) and a wave plate rotation driving device; the half wave plate (1), the quarter wave plate (2), the beam expander (6) and the light beam scanning system (8) are arranged in sequence from front to back on the output light path of the laser (12); the processing sample (11) is on the scanning path of the light beam scanning system (8) and is placed on the motion platform (10) and moves freely with the motion platform (10); the wave plate rotation driving device is respectively connected to the half wave plate (1) and the quarter wave plate (2) and drives the half wave plate (1) and the quarter wave plate (2) to rotate at high speed; the main control system (13) is respectively connected to the laser (12), the wave plate rotation driving device, the light beam scanning system (8) and the motion platform (10).

7. The polarization light modulation device according to claim 6, wherein: The wave plate rotation drive device comprises a first motor (3), a second motor (4) and a drive controller (5); the drive controller (5) is connected to the first motor (3) and the second motor (4) respectively; the main control system (13) is connected to the drive controller (5); the first motor (3) is connected to the half wave plate (1) and drives the half wave plate (1) to rotate at high speed; the second motor (4) is connected to the quarter wave plate (2) and drives the quarter wave plate (2) to rotate at high speed.

8. The polarization light modulation device according to claim 6 or 7, wherein: The polarized light modulation device further comprises a reflective mirror (7) arranged between the beam expander (6) and the beam scanning system (8), and a focusing mirror (9) arranged between the beam scanning system (8) and the processed sample (11).

9. A laser processing method based on the polarization light modulation device according to any one of claims 6 to 8, characterized in that: The laser processing method comprises the following steps: 1) constructing a polarization light modulation device as described in any one of claims 6 to 8; 2) Select different polarization states of the laser suitable for the workpiece according to the structural characteristics of the workpiece; 3) The main control system (13) controls the rotation of the half wave plate (1) and the quarter wave plate (2) respectively, so that the laser light emitted from the laser (12) forms different polarization states of the laser light required in step 2); 4) Processing the workpiece accordingly with the different polarization states of the laser light formed in step 3) until the laser processing operation is completed.

10. The laser processing method according to claim 9, wherein: The structural features of the workpiece to be processed in step 2) include a porous structure and a non-circular structure; when the structural feature of the workpiece to be processed in step 2) is a porous structure, the laser used is circularly polarized light; when the structural feature of the workpiece to be processed in step 2) is a non-circular structure, the laser used is elliptically polarized light.

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