Light spot shaping device and method based on partition modulation and polarization element customization

Abstract

The invention discloses a light spot shaping device and method based on partition modulation and a customized polarization element, and relates to the technical field of laser processing, random polarized light is divided into S / P light through a 42.5-degree customized polarization beam splitter (PBS), the S / P light is emitted to a partition silicon-based liquid crystal spatial light modulator (LCoS SLM) in parallel through a total reflection surface, the liquid crystal orientation difference of A / B regions is 90 degrees, independent modulation is achieved, and the light spot shaping device and method based on the partition modulation and the customized polarization element are obtained. And combining the light beams by using a P reflection type polarization beam splitter (R-PBS) and ensuring that the optical path is consistent. The method comprises the steps of beam expansion, light splitting, partition modulation, light beam combination, secondary beam expansion focusing and the like. According to the scheme, the energy utilization rate is close to 100%, the method is suitable for lasers of 50 W or above, the machining efficiency of the shaped annular light spots is improved by two times or above compared with Gaussian beams, the temperature gradient is reduced, the method can be used for laser welding and metal 3D printing, and the problems of energy waste, heat effect and insufficient precision 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 and method based on partition modulation and customized polarization elements. Background Art

[0002] In the field of laser processing, Gaussian beams, due to their high energy distribution at the center and low energy at the edges, present significant limitations in applications such as welding and metal 3D printing. Their energy gradient leads to uneven temperature distribution during processing, which can easily cause thermal stress cracks. Furthermore, the effective processing area is small, resulting in low efficiency. Therefore, shaping Gaussian beams into non-Gaussian beams, such as flat-top beams and annular beams, is key to improving processing quality.

[0003] In existing technologies, fiber lasers typically output randomly polarized light, while liquid crystal on silicon spatial light modulators (LCoSSLMs) can only modulate linearly polarized light. Traditional solutions use a polarization beam splitter (PBS) to split randomly polarized light into S / P polarized light, utilizing only the energy of one polarization and wasting 50% of the laser energy. Furthermore, existing public documents (such as CN116909051B) exhibit significant flaws: The optical components are too closely spaced, making it susceptible to heat accumulation under high-power laser irradiation exceeding 50W, leading to deformation of the reflective surface and affecting the beam spot accuracy. Furthermore, water cooling is not possible. The beam passes through the beam splitting surface multiple times, resulting in light loss rates as high as 10-15%.

[0004] In view of this, this application is hereby filed. Summary of the Invention

[0005] The object of the present invention is to provide a light spot shaping device and method based on partition modulation and customized polarization elements to solve the problems mentioned in the above background technology.

[0006] To solve the above technical problems, the present invention provides a light spot shaping device based on partition modulation and customized polarization elements, comprising: Fiber laser: used to output randomly polarized light; Beam expander: used to expand randomly polarized light; Customized polarization beam splitter (PBS): The beam splitting surface is designed with an angle of 42.5 degrees, which is used to split the randomly polarized light into S-polarized light and P-polarized light, where the S-polarized light is reflected and the P-polarized light is transmitted; Total reflection surface: arranged parallel to the beam splitting surface of the customized PBS, used to reflect the transmitted P-polarized light and make it parallel to the reflected S-polarized light; Liquid crystal on silicon spatial light modulator (LCoS SLM): Its active area is divided into area A and area B. The liquid crystal orientation directions of areas A and B differ by 90 degrees, and are used to receive parallel S-polarized light and P-polarized light respectively and perform phase modulation; P-type reflective polarization beam splitter (R-PBS): used to receive modulated S-polarized light and P-polarized light. The R-PBS transmits the S-polarized light and reflects the P-polarized light, combining the two into one beam. 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.

[0007] Furthermore, the angle of the splitting surface of the customized polarization beam splitter (customized PBS) is 40 to 50 degrees, and the reflection and transmission of S-polarized light and P-polarized light are achieved through the interference film of the customized splitting surface.

[0008] Furthermore, the incident angles of the S-polarized light and the P-polarized light incident on the liquid crystal on silicon spatial light modulator (LCoS SLM) are both less than or equal to 5 degrees.

[0009] Furthermore, the interference film of the P reflective polarization beam splitter (R-PBS) is designed to reflect P polarized light and transmit S polarized light, and the optical paths of the S polarized light and the P polarized light at the P reflective polarization beam splitter (R-PBS) are consistent.

[0010] Furthermore, area A and area B of the liquid crystal on silicon spatial light modulator (LCoS SLM) do not overlap, and area A corresponds to S-polarized light modulation, and area B corresponds to P-polarized light modulation.

[0011] A method for using a light spot shaping device based on partition modulation and customized polarization elements, comprising the following steps: The fiber laser outputs randomly polarized light, which is expanded to 6-13mm by a beam expander; Randomly polarized light passes through a 42.5-degree custom polarizing beam splitter (PBS), which reflects S-polarized light and transmits P-polarized light; The transmitted P-polarized light is reflected by the total reflection surface and then incident on areas A and B of the liquid crystal on silicon spatial light modulator (LCoS SLM) in parallel with the S-polarized light. The orientation of the liquid crystals in areas A and B differs by 90 degrees. Liquid crystal on silicon spatial light modulator (LCoS SLM) phase modulates the S / P polarized light to form a non-Gaussian beam; The modulated light beam is emitted to the R-PBS, the S light is transmitted, the P light is reflected and then merged into one beam; After the combined beam is expanded by the 4f optical module, it is focused onto the material surface through the scanning galvanometer module and the field lens.

[0012] Furthermore, the 4f optical module expands the beam diameter from 8 mm to 15 mm.

[0013] Furthermore, the optical paths of the S-polarized light and the P-polarized light are consistent, and the modulated non-Gaussian light beam includes but is not limited to a flat-top beam and a ring beam.

[0014] Furthermore, in one of laser welding and metal 3D printing, the energy gradient of the non-Gaussian beam is smaller than that of the Gaussian beam.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. Energy utilization rate is significantly improved, breaking through the bottleneck of 50% energy waste in traditional solutions: 1. Synergistic utilization of dual-polarized light: By customizing the design of 42.5-degree PBS and total reflection surface, randomly polarized light is divided into S / P polarized light and emitted to the A / B area of the SLM for modulation respectively. Finally, it is merged into a beam of light through the R-PBS, achieving a laser energy utilization rate of nearly 100% (traditional solutions can only utilize 50%).

[0016] 2. Precise control of energy loss: The interference film design of customized PBS can achieve total reflection of S light and full transmission of P light (reflection / transmittance ≥ 99%). If a 45-degree PBS is used, the S light transmittance and P light reflectance are controlled within 5-10%, ensuring minimal energy loss.

[0017] 2. The accuracy of light spot shaping and the consistency of optical path are significantly optimized: 1. Partition modulation and optical path matching: The liquid crystal orientation directions of the A / B zones of the SLM differ by 90 degrees, which are adapted to S / P polarized light modulation respectively. After the S / P light is processed by the total reflection surface and R-PBS, the optical path difference is ≤λ / 5 (λ is the laser wavelength), avoiding spot distortion caused by phase difference.

[0018] 2. Precise control of the incident angle: The incident angle of the S / P light to the SLM is ≤5 degrees, and the angle between the outgoing light and the incident light is ≤10 degrees, which reduces the modulation error caused by beam deviation and ensures phase loading accuracy.

[0019] 3. High-power laser applicability breaks through traditional limitations: 1. Optimized thermal management of optical components: The customized spacing design between PBS and SLM avoids the heat accumulation problem caused by the close proximity of components in traditional solutions. Combined with the heat dissipation layout of the total reflection surface, it can withstand the power density of continuous lasers or nanosecond lasers above 50W (such as 200W fiber lasers). The temperature rise of the reflecting surface is ≤10℃, which does not affect the spot shaping effect.

[0020] 2. Compatible with industrial-grade high-power processing: In metal 3D printing applications, when using 500-2000W lasers, the temperature gradient of the molten pool is reduced, avoiding splashing and cracking of the material due to sudden temperature changes, and improving the processing yield.

[0021] 4. Double improvement in processing efficiency and quality: Non-Gaussian beams have significant advantages: The shaped flat-top or annular beam has a low energy gradient, resulting in a more uniform temperature distribution during processing. Compared to Gaussian beams (which have higher energy at the center), they are more suitable for welding and melting metal powders. For example, the processing area of an annular spot is more than twice that of a Gaussian beam.

[0022] 2. Multifunctional processing adaptation: By loading different phase patterns on the SLM, non-Gaussian beams such as flat-top light and ring light can be flexibly generated.

[0023] 5. Enhanced flexibility and compatibility of optical path design Customized PBS angles are compatible with multiple scenarios: In addition to the optimal angle of 42.5 degrees, customized interference films can be adapted to different splitting angles of 40 to 50 degrees to accommodate different laser polarization characteristics and optical path layout requirements, providing increased flexibility.

[0024] The SLM partition design is adapted to polarization light modulation: the A / B zones independently modulate the S / P light, and can load the same or complementary phase patterns according to processing requirements. For example, symmetrical ring beams can be generated simultaneously, or energy uniformity can be further optimized through complementary modulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A flow chart of a method for using a light spot shaping device based on partition modulation and customized polarization elements; Figure 2 It is a complete optical path for existing fiber lasers to cooperate with SLM. DETAILED DESCRIPTION

[0026] 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.

[0027] See also Figure 1-Figure 2 The present invention provides a technical solution: a light spot shaping device and method based on partition modulation and customized polarization elements, comprising: 1. Device Construction and Optical Component Installation 1. Fiber laser installation Fix the fiber laser on the optical path base, align the output end with the center of the beam expander, and ensure that the axis of the laser collimated beam is parallel to the base guide rail.

[0028] 2. Beam expander debugging Install a beam expander (the magnification is selected according to needs, such as 1:2), adjust the position of the beam expander so that the diameter of the laser spot after beam expansion is 6-13mm (for example, from 4mm to 8mm), and monitor the beam energy using a power meter.

[0029] 3. Custom polarizing beam splitter (PBS) and total reflection surface installation A customized PBS with a fixed 42.5-degree angle is used. Its beam splitting surface forms an angle of 42.5 degrees with the incident direction of the laser, ensuring that the randomly polarized light is incident on the PBS beam splitting surface at an incident angle of 47.5 degrees (90-42.5 degrees). A total reflection surface (such as a plane mirror) is installed parallel to the PBS splitter surface at a distance of 4-13 mm behind the PBS splitter surface. The spacing error between the reflection surface and the PBS splitter surface is ≤ 0.1 mm to ensure that the transmitted P-polarized light is parallel to the reflected S-polarized light after reflection.

[0030] 4.LCoS SLM Partition Calibration Install an LCoS SLM, divide its active area into area A and area B (physical or logical partitions), and use a microscope camera to calibrate the liquid crystal orientation in areas A and B: the liquid crystal orientation in area A aligns with the vibration direction of S-polarized light (e.g., vertical), and the liquid crystal orientation in area B aligns with the vibration direction of P-polarized light (e.g., horizontal), with the angle between the two being 90 degrees. Adjust the SLM position so that the S-polarized light is incident on area A and the P-polarized light is incident on area B, with the incident angles both ≤ 5 degrees (monitored by a goniometer).

[0031] 5.P Reflective Polarizing Beam Splitter (R-PBS) Installation and Optical Path Adjustment An R-PBS is installed on the SLM outgoing light path, and its interference film is designed to transmit S-polarized light and reflect P-polarized light; The optical path length compensation plate (such as quartz glass plate) is used to adjust the optical path length of the S light and the P light so that the optical path length difference between the two at the R-PBS is ≤λ / 10 (λ is the laser wavelength) to ensure consistent modulation effect.

[0032] 6.4f Optical Module and Scanning System Installation Install a 4f optical module (composed of two lenses with the same focal length) to expand the combined R-PBS beam diameter from 8 mm to 15 mm; Install the scanning galvanometer module and field lens in sequence. Select the focal length of the field lens according to the processing requirements (such as 160mm) to ensure that the focus of the beam coincides with the material surface.

[0033] 2. Implementation process of spot shaping method 1. Laser output and beam expansion Start the fiber laser, which can output randomly polarized light with a wavelength in the range of 1000-1100nm (the power can be set to 50-2000W); The randomly polarized light is expanded to a diameter of 6 mm by a beam expander, and the center area of the beam is filtered by an aperture to reduce edge stray light.

[0034] 2. Polarized light splitting and parallelization processing 2.1 After beam expansion, the randomly polarized light is incident on the 42.5 degree custom PBS: The S-polarized light is reflected by the PBS beam splitter, and the reflection angle is 95 degrees to the incident angle (due to the 47.5-degree incident angle); The P-polarized light passes through the PBS beam splitter and is directed toward the total reflection surface at the rear. 2.2 The total reflection surface reflects the P polarized light so that its propagation direction is parallel to the S polarized light (the angle between the two is ≤ 0.5 degrees), forming parallel S light and P light beams.

[0035] 3. Partition modulation and phase loading 3.1 Parallel S light and P light are incident on area A and area B of the SLM respectively: The liquid crystal in area A applies a phase modulation pattern (such as a flat-top light phase distribution) to the S light; The liquid crystal in area B loads the same or complementary phase modulation pattern to the P light (adjusted according to the shaping target); 3.2 The modulated S light and P light are emitted from the SLM and remain parallel. The angle between the emitted light and the incident light is ≤10 degrees.

[0036] 4. Beam merging and optical path calibration 4.1 The modulated S light and P light are incident on the R-PBS: The S light passes through the R-PBS spectrometer and changes its propagation direction after being reflected by the total reflection surface; The P light is reflected by the R-PBS spectrometer and merges with the S light in the same optical path to form an S+P polarization mixed beam; 4.2 Monitor the phase consistency of the combined beam using an interferometer. If the optical path difference exceeds λ / 10, adjust the position of the R-PBS or the total reflection surface to compensate.

[0037] 5. Secondary beam expansion and focusing processing 5.1 The combined beam enters the 4f optical module, and the lens group expands the spot diameter from 8mm to 15mm, thereby increasing the beam coverage area; 5.2 The expanded beam is deflected by the scanning galvanometer module and focused by the field lens onto the surface of the metal material (such as a stainless steel powder bed) for laser welding or 3D printing: Flat-top beams are used to heat materials evenly; The annular beam is used to expand the processing area, and the processing efficiency is more than 2 times higher than that of the Gaussian beam.

[0038] 3. Key parameter debugging and error control 1. PBS spectral efficiency verification Use a polarimeter to measure the energy of S light and P light after passing through 42.5 degree PBS: Under ideal conditions, the S light reflectivity is ≥99%, and the P light transmittance is ≥99%; If 45-degree PBS is used, the S light transmittance and P light reflectance are controlled within 5-10%.

[0039] 2. SLM partition incident angle calibration The incident position of the beam on the SLM is observed by an infrared CCD camera: The deviation between the center of the light spot in area A and the incident point of light S is ≤0.1mm; The deviation between the center of the light spot in area B and the incident point of light P is ≤0.1mm, ensuring that there is no overlap in the partition modulation.

[0040] A method for a spot shaping device based on partition modulation and customized polarization elements is used to reduce the temperature gradient of the molten pool and improve processing efficiency when processing 316L stainless steel powder.

Claims

1. A spot shaping device based on partition modulation and customized polarization elements, characterized by: include: Fiber laser: used to output randomly polarized light; Beam expander: used to expand randomly polarized light; Customized polarization beam splitter: The beam splitting surface is designed with an angle of 42.5 degrees, which is used to split the randomly polarized light into S-polarized light and P-polarized light, where the S-polarized light is reflected and the P-polarized light is transmitted; Total reflection surface: arranged parallel to the beam splitting surface of the customized PBS, used to reflect the transmitted P-polarized light and make it parallel to the reflected S-polarized light; Liquid crystal on silicon spatial light modulator: Its active area is divided into area A and area B. The liquid crystal orientation directions of area A and area B differ by 90 degrees, and are used to receive parallel S-polarized light and P-polarized light respectively and perform phase modulation; P-type reflective polarization beam splitter: used to receive modulated S-polarized light and P-polarized light. The P-type reflective polarization beam splitter transmits the S-polarized light and reflects the P-polarized light, combining the two into one beam. 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 partition modulation and customized polarization elements according to claim 1, characterized in that: The angle of the splitting surface of the customized polarization beam splitter also includes one of 40 to 50 degrees, and the reflection and transmission of S-polarized light and P-polarized light are achieved through the interference film of the customized splitting surface.

3. The light spot shaping device based on partition modulation and customized polarization elements according to claim 1, characterized in that: The incident angles of the S-polarized light and the P-polarized light incident on the LCOS spatial light modulator are both less than or equal to 5 degrees.

4. The light spot shaping device based on partition modulation and customized polarization elements according to claim 1, characterized in that: The interference film of the P-reflective polarization beam splitter is designed to reflect P-polarized light and transmit S-polarized light, and the optical paths of the S-polarized light and the P-polarized light at the P-reflective polarization beam splitter are consistent.

5. The light spot shaping device based on partition modulation and customized polarization elements according to claim 1, characterized in that: Region A and region B of the LCOS spatial light modulator do not overlap, and region A corresponds to S-polarized light modulation, while region B corresponds to P-polarized light modulation.

6. A method for using a light spot shaping device based on partition modulation and customized polarization elements, characterized by: The following steps are involved: The fiber laser outputs randomly polarized light, which is expanded to 6-13mm by a beam expander; Randomly polarized light passes through a 42.5-degree custom polarization beam splitter, which reflects S-polarized light and transmits P-polarized light; After being reflected by the total reflection surface, the transmitted P-polarized light is directed parallel to the S-polarized light toward areas A and B of the LCOS spatial light modulator, where the orientation directions of the liquid crystals in areas A and B differ by 90 degrees. The liquid crystal on silicon spatial light modulator phase modulates the S / P polarized light to form a non-Gaussian beam; The modulated light beam is directed to the P reflective polarization beam splitter, the S light is transmitted, the P light is reflected and merged into one beam; After the combined beam is expanded by the 4f optical module, it is focused onto the material surface through the scanning galvanometer module and the field lens.

7. A method for using a spot shaping device based on partition modulation and customized polarization elements according to claim 6, characterized in that: The 4f optical module expands the beam diameter from 8 mm to 15 mm.

8. The method for using the spot shaping device based on partition modulation and customized polarization elements according to claim 6, characterized in that: The optical paths of the S-polarized light and the P-polarized light are consistent, and the modulated non-Gaussian light beam includes but is not limited to a flat-top beam and a ring beam.

9. The method for using the spot shaping device based on partition modulation and customized polarization elements according to claim 6, characterized in that: Used in laser welding and metal 3D printing, the energy gradient of the non-Gaussian beam is smaller than that of the Gaussian beam.

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