Wave plate polarization conversion-based light spot shaping device and use method

Abstract

The invention discloses a light spot shaping device based on wave plate polarization conversion and a use method, and relates to the technical field of laser processing, the device divides random polarized light into S / P light through a first polarization beam splitter (PBS), converts the S light into P light through a first 1 / 2 wave plate, modulates the S light through a conventional silicon-based liquid crystal spatial light modulator (LCoS SLM), and converts the P light into the S light through a second 1 / 2 wave plate. And the beams are combined by the second PBS. The method comprises the steps of light splitting, polarization conversion, phase modulation, beam combining, beam expanding and focusing and the like. The double 1 / 2 wave plates are combined with the conventional PBS, the laser energy utilization rate is higher than 85%, commercial SLM equipment is adapted, the machining efficiency of the shaped annular light spots is remarkably improved compared with that of Gaussian beams, the method is suitable for laser welding and metal 3D printing, and the problems of energy waste and high cost are solved.

Description

Technical Field

[0001] The present invention relates to the field of laser processing technology, and in particular to a light spot shaping device based on wave plate polarization conversion and a use method thereof. Background Art

[0002] In the field of laser processing, shaping a Gaussian beam into a non-Gaussian beam, such as a flat-top beam or annular beam, is key to improving processing quality. Non-Gaussian beams offer advantages such as uniform energy distribution and a large processing area. For example, an annular spot can increase processing efficiency by more than 2 times and reduce temperature gradients by over 80%.

[0003] However, fiber lasers typically output randomly polarized light, while liquid crystal on silicon spatial light modulators (LCoS SLMs) can only modulate linearly polarized light. Traditional solutions can only utilize 50% of the laser energy after splitting it through a polarization beam splitter (PBS), and the remaining energy is wasted, resulting in low laser power efficiency and increased energy consumption costs.

[0004] Existing spot shaping technologies still face a challenge: when used with high-power lasers, the close spacing of optical components can easily lead to heat accumulation, affecting spot accuracy. For example, the solution described in CN116909051B is not suitable for lasers above 50W. Therefore, a spot shaping solution that improves energy utilization, is compatible with conventional optical components, and reduces costs is urgently needed to meet the efficiency and cost requirements of industrial-grade processing.

[0005] In view of this, this application is hereby filed. Summary of the Invention

[0006] The object of the present invention is to provide a light spot shaping device based on wave plate polarization conversion and a method of use to solve the problems mentioned in the above background technology.

[0007] In order to solve the above technical problems, the present invention provides a light spot shaping device based on wave plate polarization conversion, comprising: Fiber laser: used to output randomly polarized light; A first polarization beam splitter (PBS) is used to split the randomly polarized light into S-polarized light and P-polarized light, wherein the S-polarized light is reflected and the P-polarized light is transmitted; First half-wave plate: placed on the path of the S-polarized light reflected by the first polarization beam splitter (PBS) to convert the S-polarized light into P-polarized light; Liquid crystal on silicon spatial light modulator (LCoS SLM): used to receive the P-polarized light converted by the first 1 / 2 wave plate and the P-polarized light transmitted by the first polarization beam splitter (PBS), and perform phase modulation on both; Second half-wave plate: placed in the path of the P-polarized light modulated by the liquid crystal on silicon spatial light modulator (LCoS SLM) to convert the P-polarized light back to S-polarized light; Second polarization beam splitter (PBS): used to receive the S-polarized light converted by the second half-wave plate and another beam of P-polarized light modulated by the liquid crystal on silicon spatial light modulator (LCoS SLM). The second polarization beam splitter (PBS) reflects the S-polarized light and transmits the P-polarized light, combining the two into one beam of light; 4f optical module: used to expand or shrink the combined light beam; Scanning galvanometer module and field lens: used to focus the light beam onto the surface of the processing material.

[0008] Furthermore, the fast axis direction of the first half-wave plate forms an angle of 45 degrees with the vibration direction of the S-polarized light, and the fast axis direction of the second half-wave plate forms an angle of 45 degrees with the vibration direction of the P-polarized light.

[0009] Furthermore, the effective area of ​​the silicon-based liquid crystal spatial light modulator (LCoS SLM) is divided into a first area and a second area, the first area receives P-polarized light converted by the first 1 / 2 wave plate, and the second area receives P-polarized light transmitted by the first polarization beam splitter (PBS), and the liquid crystal orientation directions of the first area and the second area are the same.

[0010] Furthermore, in the light beam combined by the second polarization beam splitter (PBS), the propagation directions of the S-polarized light and the P-polarized light are the same and the optical path difference is less than 1 / 4 of the laser wavelength.

[0011] A method for using a light spot shaping device based on wave plate polarization conversion comprises the following steps: The fiber laser outputs randomly polarized light, which is split into S-polarized light and P-polarized light by the first polarization beam splitter (PBS); The S-polarized light is converted into P-polarized light by the first half-wave plate; The liquid crystal on silicon spatial light modulator (LCoS SLM) phase modulates the converted P-polarized light and the P-polarized light transmitted by the first polarization beam splitter (PBS). The modulated P-polarized light is converted back to S-polarized light through the second half-wave plate; The second polarization beam splitter (PBS) combines the converted S-polarized light with another modulated P-polarized light. The combined light beam is expanded by the 4f optical module and then focused onto the material surface through the scanning galvanometer module and the field lens.

[0012] Furthermore, the liquid crystal on silicon spatial light modulator (LCoS SLM) applies the same phase modulation pattern to the two beams of P polarized light to generate, including but not limited to, a flat top beam and a ring beam.

[0013] A method for using a light spot shaping device based on wave plate polarization conversion is used in laser welding and metal 3D printing. The uniformity of the energy distribution of the shaped beam is greater than 90%.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. Significantly improved energy utilization: Through the polarization state conversion design of dual 1 / 2 wave plates, the S / P polarized light in the randomly polarized light is synergistically utilized, and the laser energy utilization rate is increased from 50% of the traditional solution to more than 85%, reducing the energy load of the beam recovery box.

[0015] 2. Significantly reduced hardware costs, compatible with conventional optical components and industrial equipment: Using standard half-wave plates and conventional polarizers (PBSs), the system eliminates the need for custom partitioned liquid crystal SLMs (SLMs) or specialized polarization elements. Furthermore, the optical path is compatible with existing conventional SLMs (such as commercial LCoS SLMs with consistent liquid crystal orientation), eliminating the need for internal structural modifications. This facilitates rapid integration into industrial production lines and reduces debugging difficulties. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a flow chart of a light spot shaping device based on wave plate polarization conversion and its use method; Figure 2 It is a complete optical path for existing fiber lasers to cooperate with SLM. DETAILED DESCRIPTION

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0018] See also Figure 1-Figure 2 The present invention provides a technical solution: a light spot shaping device based on wave plate polarization conversion and a method of use, comprising: 1. Device construction and optical component installation: 1. Installation of fiber laser and first polarization beam splitter (PBS) Fix the fiber laser to the optical path base, align the output end with the center of the first polarization beam splitter (PBS), and adjust the laser position so that the randomly polarized light is incident on the PBS splitting surface at a 45-degree angle; Install the first PBS, ensuring that it reflects S-polarized light and transmits P-polarized light. Use a polarimeter to test the splitting efficiency: S-light reflectivity ≥ 95%, P-light transmittance ≥ 95%.

[0019] 2.1 / 2 Wave Plate Calibration and Installation The first half-wave plate is installed in the path of the S-polarized light reflected by the PBS. The polarization state analyzer is used to adjust the fast axis of the wave plate so that the fast axis forms a 45-degree angle with the vibration direction of the S-polarized light (for example, if the S light is vertically polarized, the fast axis of the wave plate is adjusted to a 45-degree azimuth angle). This converts the S light into P-polarized light after passing through the wave plate. The second half-wave plate is installed between the liquid crystal on silicon spatial light modulator (LCoS SLM) and the second PBS. The fast axis direction is at a 45-degree angle to the vibration direction of the P-polarized light, and is used to convert the P light back into S light.

[0020] 3. Liquid Crystal on Silicon Spatial Light Modulator (LCoS SLM) and Second PBS Installation Install a conventional LCoS SLM (with consistent liquid crystal orientation in each partition) so that the P light converted by the first half-wave plate and the P light transmitted by the PBS are incident on different areas of the SLM (such as the left and right partitions) respectively, with an incident angle of ≤10 degrees; A second PBS is installed on the SLM output light path, and its position is adjusted so that the modulated S light (converted by the second 1 / 2 wave plate) and the P light are combined at the second PBS, and the combined optical path difference is ≤λ / 4 (λ is the laser wavelength).

[0021] 4.4f Optical Module and Scanning System Installation Install a 4f optical module (lens focal length 100mm) to expand the combined beam spot diameter from 8mm to 15mm; Install the scanning galvanometer module and field lens (focal length 160mm) in sequence, and use the cross cursor to calibrate the overlap between the beam focus and the material surface.

[0022] 2. Implementation process of spot shaping method: 1. Laser output and polarization splitting Start the fiber laser (wavelength 1064nm, power 50-2000W) to output randomly polarized light; The randomly polarized light is split by the first PBS: the S light is reflected and the P light is transmitted. The energy after splitting is measured with a power meter: the S light accounts for about 50% and the P light accounts for about 50%.

[0023] 2. Polarization conversion and modulation The S light passes through the first half-wave plate, is converted into P polarized light, and is incident on the first region of the SLM; The P light transmitted by the first PBS is directly incident on the second region of the SLM; The SLM applies the same phase modulation pattern (such as the phase distribution of annular light) to the two P beams, and the modulation voltage is set to 1-10V to ensure that the phase delay is adjustable from 0 to 2π.

[0024] 3. Secondary polarization conversion and beam combining The modulated P light passes through the second half-wave plate and is converted back to S polarized light; The second PBS processes the beam: The P light modulated by the first region of the SLM passes through the second PBS; The S light passing through the second half-wave plate is reflected by the second PBS; The two are combined into one beam after the second PBS, and the optical path difference is detected by an interferometer. If it exceeds λ / 4, the position of the second PBS is adjusted.

[0025] 4. Beam expansion, focusing and processing The combined light is expanded to 15mm by the 4f module, and the energy uniformity is ≥85%; The scanning galvanometer module controls the beam deflection, and the field lens focuses on the surface of the stainless steel powder (316L) for 3D printing: The annular spot processing speed is 1000mm / s, the single layer thickness is 50μm, and the efficiency is increased by 1.8 times compared with Gaussian beam; The temperature gradient of the molten pool is ≤5℃ / mm, which is lower than the 15℃ / mm of the Gaussian beam.

[0026] 3. Key parameter debugging and error control: Verification of polarization conversion efficiency of 1.1 / 2 wave plate Use a polarimeter to measure the polarization state of the light after the first 1 / 2 wave plate: the conversion efficiency of S light to P light is ≥98%, and the residual S light energy is ≤2%; The efficiency of the second 1 / 2 wave plate in converting P light into S light is ≥98%, and the residual P light energy is ≤2%.

[0027] 2. SLM incident light spot calibration Observe the light spot distribution on the SLM using an infrared CCD camera: The deviation between the center of the first area spot and the incident point of the converted P light is ≤0.1mm; The deviation between the center of the light spot in the second area and the incident point of the P light is ≤0.1mm to avoid modulation interference caused by light spot overlap.

[0028] 3. Beam combining optical path consistency test The optical path difference between the S light and the P light after the combined beam is measured using a Michelson interferometer. By adjusting the distance between the second half-wave plate and the second PBS, the optical path difference is ≤50nm (corresponding to λ / 20 of 1064nm laser) to ensure phase synchronization.

[0029] When used to process 316L stainless steel, the Gaussian beam is shaped into a ring beam, with an energy distribution uniformity of 92%, an energy difference between the edge and the center of ≤8%, and energy utilization increased from 50% of the traditional solution to 87%.

Claims

1. A light spot shaping device based on wave plate polarization conversion, characterized by: include: Fiber laser: used to output randomly polarized light; A first polarization beam splitter is used to split the randomly polarized light into S-polarized light and P-polarized light, wherein the S-polarized light is reflected and the P-polarized light is transmitted; First 1 / 2 wave plate: It is placed on the path of the S-polarized light reflected by the first polarization beam splitter and is used to convert the S-polarized light into P-polarized light; Liquid crystal on silicon spatial light modulator: used to receive the P-polarized light converted by the first half-wave plate and the P-polarized light transmitted by the first polarization beam splitter, and perform phase modulation on both; Second half-wave plate: placed on the path of the P-polarized light modulated by the LCOS spatial light modulator, used to convert the P-polarized light back to S-polarized light; A second polarization beam splitter is used to receive the S-polarized light converted by the second half-wave plate and another beam of P-polarized light modulated by the liquid crystal on silicon spatial light modulator, wherein the second polarization beam splitter reflects the S-polarized light and transmits the P-polarized light, so that the two are combined into one beam of light; 4f optical module: used to expand or shrink the combined light beam; Scanning galvanometer module and field lens: used to focus the light beam onto the surface of the processing material.

2. The light spot shaping device based on wave plate polarization conversion according to claim 1, characterized in that: The fast axis direction of the first half-wave plate forms an angle of 45 degrees with the vibration direction of the S-polarized light, and the fast axis direction of the second half-wave plate forms an angle of 45 degrees with the vibration direction of the P-polarized light.

3. The light spot shaping device based on wave plate polarization conversion according to claim 1, characterized in that: The effective area of ​​the silicon-based liquid crystal spatial light modulator is divided into a first area and a second area. The first area receives P-polarized light converted by the first 1 / 2 wave plate, and the second area receives P-polarized light transmitted by the first polarization beam splitter. The liquid crystal orientation directions of the first and second areas are the same.

4. The light spot shaping device based on wave plate polarization conversion according to claim 1, characterized in that: In the light beam merged by the second polarization beam splitter, the propagation directions of the S-polarized light and the P-polarized light are the same and the optical path difference is less than 1 / 4 of the laser wavelength.

5. A method for using a light spot shaping device based on wave plate polarization conversion, characterized in that: Follow these steps: The fiber laser outputs randomly polarized light, which is divided into S-polarized light and P-polarized light by the first polarization beam splitter; The S-polarized light is converted into P-polarized light by the first half-wave plate; The liquid crystal on silicon spatial light modulator performs phase modulation on the converted P-polarized light and the P-polarized light transmitted by the first polarization beam splitter respectively; The modulated P-polarized light is converted back to S-polarized light through the second half-wave plate; The second polarization beam splitter combines the returned S-polarized light with another modulated P-polarized light; The combined light beam is expanded by the 4f optical module and then focused onto the material surface through the scanning galvanometer module and the field lens.

6. The method for using the light spot shaping device based on wave plate polarization conversion according to claim 5, characterized in that: The liquid crystal on silicon spatial light modulator applies the same phase modulation pattern to two beams of P polarized light to generate, including but not limited to, a flat top beam and a ring beam.

7. The method for using the light spot shaping device based on wave plate polarization conversion according to claim 5, characterized in that: It is used for but not limited to laser welding and metal 3D printing, and the uniformity of the energy distribution of the shaped beam is greater than 90%.

Images