Three-step polishing method for inhibiting high-frequency error in CO2 laser polishing of fused quartz element
By employing a three-step polishing method that combines acid etching and laser preheating with high-speed multilayer and low-speed single-layer polishing, the problem of high-frequency errors in CO2 laser polishing of fused silica components has been solved. This improves the optical transmission performance and resistance to laser damage of optical components, extends their service life, and reduces material consumption.
Patent Information
- Application Number
- CN202511621216.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-07
- Publication Date
- 2025-12-09
AI Technical Summary
In the CO2 laser polishing process of fused silica elements, the existing technology suffers from mid-to-high frequency errors that lead to far-field light modulation and near-field light field enhancement, affecting optical transmission performance and resistance to laser damage, and limiting the output throughput of high-power solid-state laser devices.
A three-step polishing method is adopted, including acid etching, laser preheating, high-speed multi-layer polishing, and low-speed single-layer polishing. By controlling the laser parameters and moving speed, high-frequency errors on the surface of the fused silica element are gradually eliminated.
It significantly reduces the surface mid-to-high frequency and high-frequency errors of fused silica elements, improves light transmission performance and resistance to laser damage, extends the service life of the elements, and reduces material consumption and processing time.
Smart Images
Figure CN121083101A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of laser processing technology for optical components, and more specifically, to a three-step polishing method for suppressing high-frequency errors in CO2 laser polishing of fused silica components. Background Technology
[0002] High-power solid-state laser devices are an important means of conducting high-energy physics experiments under laboratory conditions. These devices use thousands of large-aperture fused silica optical elements. The laser damage resistance of these optical elements determines the output flux of the high-power solid-state laser device. Therefore, improving the laser damage resistance of large-aperture fused silica elements is a bottleneck problem in improving the output flux of high-power solid-state laser devices.
[0003] Currently, contact mechanical polishing inevitably introduces surface and subsurface defects into the surface of fused silica elements. These defects are highly susceptible to laser damage under strong laser irradiation, and this damage rapidly expands with subsequent laser irradiation, leading to the rapid failure of the fused silica element. Because fused silica has a high energy absorption rate for CO2 lasers with a wavelength of 10.6µm, under CO2 laser irradiation, the surface material of the fused silica element can convert laser energy into heat, raising its temperature above the melting point, thereby achieving melt healing of surface defects and significantly improving the laser damage resistance of the fused silica element. However, in actual processing, the thermal accumulation effect after prolonged laser exposure and the surface grooves formed by the laser's trajectory lead to the formation of high-frequency errors on the surface of the fused silica element. Simultaneously, insufficient melting and flow of the material leaves pits and other defects on the surface of the fused silica element, contributing to high-frequency errors. Mid-to-high frequency errors-induced far-field optical modulation and high-frequency errors-induced near-field optical field enhancement severely affect the optical transmission performance and laser damage resistance of fused silica elements, limiting the engineering application of CO2 laser polishing technology for fused silica elements and the improvement of output flux in high-power solid-state laser devices. Therefore, to address these problems, this invention proposes a three-step polishing method to suppress mid-to-high frequency errors in CO2 laser polishing of fused silica elements. This method suppresses mid-to-high frequency and high-frequency errors on the surface of fused silica elements, ultimately achieving high-performance ultra-precision machining of the fused silica element surface. Summary of the Invention
[0004] The technical problem to be solved by this invention is:
[0005] To address the problem that high-frequency errors induce far-field optical modulation and high-frequency errors induce near-field optical field enhancement when laser-processing fused silica components, which severely affect their optical transmission performance and resistance to laser damage.
[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:
[0007] This invention provides a three-step polishing method for suppressing high-frequency errors in CO2 laser polishing of fused silica elements, comprising the following steps:
[0008] S100. The mechanically ground fused silica element is acid-etched to expose subsurface defects, and then cleaned to obtain the initial fused silica element before polishing.
[0009] S200: Install the initial fused silica element obtained in step S100 onto the XY moving platform fixture for laser polishing, draw the moving trajectory for laser preheating, and set the laser preheating parameters to perform the first step of preheating;
[0010] S300. Draw the movement trajectory for the second step of high-speed multi-layer polishing, set the high-speed multi-layer polishing parameters, and perform the second step of high-speed multi-layer polishing.
[0011] S400: Set the parameters for the third step of low-speed single-layer polishing, and perform the third step of low-speed single-layer polishing according to the movement trajectory for the second step of high-speed multi-layer polishing drawn in step S300.
[0012] S500: Clean the fused silica element after three polishing processes to obtain the laser-polished fused silica element.
[0013] Furthermore, in step S100, the surface roughness Ra of the fused silica element after mechanical grinding is 100nm-200nm, and the etching depth during acid etching is 10μm-20μm.
[0014] Furthermore, in step S200, during the first preheating step, the heating temperature of the surface material of the fused quartz element is above 1000K and below the melting temperature of 2273K.
[0015] Furthermore, in step S200, the laser preheating parameters include laser beam diameter, power, duty cycle, repetition frequency, phase difference, and spot movement speed.
[0016] Furthermore, in step S300, during the second high-speed multilayer polishing, the maximum thermodynamic temperature of the surface material of the fused silica element exceeds the melting temperature of 2273K, but is lower than the evaporation temperature of the fused silica material of 2973K.
[0017] Furthermore, in step S400, the maximum thermodynamic temperature of the surface material in the third step of low-speed single-layer polishing exceeds the maximum thermodynamic temperature of the material during the laser polishing process in step S300, but is lower than the evaporation temperature of the fused silica material, which is 2973K.
[0018] Furthermore, the laser moving speed during the second step of high-speed multi-layer polishing is greater than 1 mm / s, while the laser moving speed during the third step of low-speed single-layer polishing is less than 1 mm / s.
[0019] Furthermore, the number of polishing layers in the second step of high-speed multi-layer polishing is five, and the number of polishing layers in the third step of low-speed single-layer polishing is one.
[0020] Compared with the prior art, the beneficial effects of the present invention are:
[0021] 1. Through an innovative three-step laser polishing strategy, the mid-to-high frequency and high-frequency errors on the surface of fused silica components after laser polishing are significantly reduced. The processed surface is almost free of surface tool marks, which effectively reduces the far-field light modulation and near-field light field enhancement effects and increases the damage performance of the components under strong laser irradiation conditions.
[0022] 2. The laser preheating process effectively reduces the cooling rate of the material after polishing, thereby reducing the hypothetical temperature and residual stress of the modified layer of the fused silica element after polishing (hypothetical temperature and residual stress are related; excessive residual stress can cause cracks in the processed element under stress, leading to the scrapping of the element. The formation of residual stress is closely related to the temperature difference and the cooling rate of the material. After laser preheating, the temperature of the entire element substrate rises, thus reducing the temperature difference between the surface and internal materials during laser processing. After processing, the cooling rate of the material slows down, which can reduce residual stress). This increases the service life of the element (the stress reduction makes it less prone to cracking and scrapping). At the same time, the higher substrate temperature after preheating reduces the laser energy required for the polishing process.
[0023] 3. Compared with traditional subtractive processing methods such as mechanical polishing, this processing method does not remove any material, which can reduce material consumption; as a non-contact processing method, it does not introduce new surface or subsurface defects, and the laser action process is fast and the processing efficiency is high. Attached Figure Description
[0024] Figure 1 This is a schematic diagram of the optical path of the CO2 laser polishing system in an embodiment of the present invention;
[0025] Figure 2 This is a schematic diagram of the steps in a three-step polishing method for suppressing high-frequency errors in CO2 laser polishing of fused silica elements according to an embodiment of the present invention;
[0026] Figure 3 This is a flowchart of the three-step polishing method in an embodiment of the present invention;
[0027] Figure 4 This is a schematic diagram of the laser preheating trajectory and parameters in an embodiment of the present invention;
[0028] Figure 5 This is a comparison diagram of the light transmittance of the fused silica element before and after laser polishing in an embodiment of the present invention;
[0029] Figure 6This is a comparison chart of mid-to-high frequency errors before and after using the three-step polishing method in an embodiment of the present invention. Detailed Implementation
[0030] In the description of this invention, it should be noted that the terms used in the various embodiments, such as "upper," "lower," "front," "rear," "left," and "right," which indicate orientation, are only used to simplify the description of the positional relationships based on the accompanying drawings and do not mean that the components and devices referred to must be operated in accordance with the specific orientations and defined operations, methods, and structures in the specification. Such directional terms do not constitute a limitation of this invention.
[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
[0032] The optical path diagram of the laser processing system used in laser polishing is as follows: Figure 1 As shown, the optical path of the processing system includes a CO2 laser optical path modulation system, a two-dimensional galvanometer scanning system, and an XY moving platform. This processing system can achieve CO2 laser polishing of 100mm × 100mm fused silica elements. The two-dimensional galvanometer system is located on the Z-axis moving platform, and the diameter of the CO2 laser spot irradiating the surface of the fused silica element can be adjusted by moving the position of the galvanometer system; the CO2 laser optical path modulation system realizes the optical transmission of CO2 laser, and the laser polishing of the fused silica surface is achieved through focusing by the galvanometer system and the field lens.
[0033] Specific Implementation Plan 1: Combining Figures 1 to 3 As shown, this invention provides a three-step polishing method for suppressing high-frequency errors in CO2 laser polishing of fused silica elements, comprising the following steps:
[0034] S100. The mechanically ground fused silica element is immersed in hydrofluoric acid solution for acid etching to remove surface contaminants and impurities and expose subsurface defects. It is then cleaned with deionized water to obtain the initial fused silica element before laser polishing.
[0035] The fused silica element is a mechanically ground fused silica element with a surface roughness Ra of 100nm-200nm and has surface and subsurface defects. Acid etching is a hydrofluoric acid etching of the fused silica element with an etching depth of 10μm-20μm.
[0036] S200. Mount the fused silica element on the fixture of the XY moving platform, draw the laser movement trajectory for laser preheating, set the parameters used in the preheating process for the first step of laser preheating of the fused silica element, move the XY moving platform to move the center of the laser spot to the starting position of the drawn processing trajectory, and turn on the laser to perform the first step of preheating of the fused silica element.
[0037] Using a CO2 laser to heat the surface material of a fused silica element to above 1000K and below the melting temperature of 2273K, the fused silica material in the polishing area has a thermodynamic temperature above 1000K. This reduces the problems of excessive residual stress and insufficient material melt flow caused by excessively rapid material cooling during laser polishing. The laser movement trajectory refers to the movement trajectory of the laser spot center during laser preheating. This trajectory is typical for CO2 laser processing of fused silica elements, i.e., triggered from an initial point, moving from one end of a row to the other, then moving to the next row, and so on, completing laser preheating row by row. The parameters used in the preheating process include laser beam diameter, power, duty cycle, repetition frequency, phase difference, and spot movement speed.
[0038] S300. Draw the polishing trajectory used in the second step of laser polishing, set the parameters used in the second step of high-speed multi-layer polishing, move the XY moving platform to move the center of the laser spot to the starting position of the processing trajectory, and turn on the laser to perform the second step of high-speed multi-layer polishing on the fused silica element.
[0039] The second step, high-speed multi-layer polishing, involves laser polishing of the fused silica element using a high laser movement speed. During the polishing process, the maximum thermodynamic temperature of the surface material exceeds the melting temperature of 2273K. After polishing, the surface pits and protrusions are gradually smoothed under the action of surface tension. After high-frequency filtering (10μm <λ < 100μm), the surface roughness Sa is less than 10nm, where λ is the spatial wavelength, representing the length period of multiple occurrences of a uniform morphology in signal processing. At the same time, there is no obvious tool mark structure formed by the processing trajectory on the surface. After mid-to-high frequency filtering, the surface roughness Sa is less than 25nm (100μm <λ < 2500μm).
[0040] The parameters used in the second step of high-speed multi-layer polishing are the same as those in step S200.
[0041] The second step, high-speed multi-layer polishing, uses a high laser moving speed (greater than 1 mm / s) to polish the fused silica element from beginning to end along the polishing trajectory, and the surface roughness after polishing meets the aforementioned requirements.
[0042] S400, set the parameters used for the third step of low-speed single-layer polishing, and turn on the laser to perform the third step of low-speed single-layer polishing on the fused silica element.
[0043] The third step, low-speed single-layer polishing, involves using a relatively low laser moving speed (less than 1 mm / s) to perform single-layer laser polishing on the fused silica surface processed in step S300 according to the trajectory drawn in step S300. During the polishing process, the maximum thermodynamic temperature of the surface material exceeds the maximum thermodynamic temperature of the material during the laser polishing process in step S300, but is lower than the evaporation temperature of the fused silica material, 2973 K. Due to the decrease in speed, the interaction time between the laser and the material increases, resulting in a lower material temperature and a higher temperature during the second and third processing steps, respectively. However, the temperature range of steps S300 and S400 is within 2273 K to 2973 K.
[0044] After polishing, the surface roughness Sa after high-frequency filtering (10μm <λ<100μm) is less than 3nm, and the surface roughness Sa after medium-high frequency filtering (10μm <λ<100μm) is less than 20nm; the polishing parameters are the same type as those in step S200;
[0045] The trajectory planning, parameter setting, and laser preheating polishing process for steps S200-S400 are as follows: Figure 3 As shown;
[0046] The S500 uses deionized water to clean the surface of the polished fused silica element, removing impurities and contaminants deposited on the element surface, thus completing the laser polishing of the fused silica element.
[0047] experiment
[0048] 1) Etching of fused silica elements with hydrofluoric acid solution
[0049] The Corning 7980 fused silica element, after mechanical grinding, measures 50×50×5mm. 3 The fused silica element is immersed in hydrofluoric acid solution for 2 hours for hydrofluoric acid etching. After the impurities, contaminants and surface defects are passivated, the fused silica element is removed and cleaned with deionized water to obtain a fused silica element to be polished without grinding fluid and etching fluid residue.
[0050] 2) Laser in-situ preheating
[0051] After etching and cleaning, the fused silica element is mounted onto the fixture of the XY moving platform. Based on the dimensions of the fused silica element, the laser preheating trajectory of the fused silica element is plotted. The parameters and trajectory are as follows: Figure 4 As shown in Table 1, move the laser platform to the center of the processing area, adjust the defocus distance to 12mm, and make the laser spot diameter reach 2mm. Adjust the laser power to 20W, the laser moving speed to 5mm / s, and other parameters as shown in Table 1. Turn on the laser and let the laser preheat the fused silica element according to the drawn preheating trajectory.
[0052] Table 1 CO2 Laser Preheating Parameters
[0053]
[0054] 3) High-speed laser multi-layer polishing
[0055] After the fused silica element has been preheated, a high-speed multi-layer laser polishing trajectory is plotted. The laser power is adjusted to 30W, the laser moving speed to 1.5mm / s, the scanning interval to 0.2mm, and the number of polishing layers to 5. All other parameters remain unchanged. The laser is then turned on to perform high-speed multi-layer polishing on the fused silica element.
[0056] 4) Laser low-speed single-layer polishing
[0057] Adjust the laser movement speed to 1 mm / s, the number of polishing layers to 1, and keep the other parameters unchanged. Turn on the laser to perform low-speed single-layer polishing on the fused silica element.
[0058] 5) Cleaning with deionized water
[0059] After the fused silica element cooled, it was removed from the moving platform and its surface was cleaned with deionized water. Subsequently, a camera was used to measure the light transmittance and surface smoothness of the fused silica element, and a white light interferometer was used to measure the high-frequency errors on the surface of the fused silica element. First, the surface smoothness and light transmittance of the fused silica element before and after polishing were compared. Figure 5 As shown, the fused silica element exhibits good light transmittance after polishing.
[0060] The high-frequency error curves of the laser-polished fused silica element surface before and after the three-step polishing method were compared. Figure 6 As shown, the mid-to-high frequency error is the surface roughness value after filtering within the spatial wavelength range of greater than 120 μm and less than 2500 μm, and the high frequency error is the surface roughness value after filtering within the spatial wavelength range of greater than 10 μm and less than 120 μm. Testing showed that the mid-to-high frequency error of the fused silica element decreased from 47 nm to 17.7 nm, and the high frequency error decreased from 8.4 nm to 1.5 nm. Figure 6 As shown in the figure. Experimental results show that this three-step polishing method can effectively reduce heat accumulation and excessive material melting and flow caused by laser polishing, and effectively suppress medium and high frequency errors.
[0061] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.
Claims
1. A three-step polishing method for suppressing high-frequency errors in CO2 laser polishing of fused silica elements, characterized in that, Includes the following steps: S100. The mechanically ground fused silica element is acid-etched to expose subsurface defects, and then cleaned to obtain the initial fused silica element before polishing. S200: Install the initial fused silica element obtained in step S100 onto the XY moving platform fixture for laser polishing, draw the moving trajectory for laser preheating, and set the laser preheating parameters to perform the first step of preheating; S300. Draw the movement trajectory for the second step of high-speed multi-layer polishing, set the high-speed multi-layer polishing parameters, and perform the second step of high-speed multi-layer polishing. S400: Set the parameters for the third step of low-speed single-layer polishing, and perform the third step of low-speed single-layer polishing according to the movement trajectory for the second step of high-speed multi-layer polishing drawn in step S300. S500: Clean the fused silica element after three polishing processes to obtain the laser-polished fused silica element.
2. The three-step polishing method for suppressing high-frequency errors in CO2 laser polishing of fused silica elements according to claim 1, characterized in that: In step S100, the surface roughness Ra of the fused silica element after mechanical grinding is 100nm-200nm, and the etching depth during acid etching is 10μm-20μm.
3. The three-step polishing method for suppressing high-frequency errors in CO2 laser polishing of fused silica elements according to claim 2, characterized in that: In step S200, during the first preheating step, the heating temperature of the surface material of the fused quartz element is above 1000K and below the melting temperature of 2273K.
4. The three-step polishing method for suppressing high-frequency errors in CO2 laser polishing of fused silica elements according to claim 3, characterized in that: In step S200, the laser preheating parameters include laser beam diameter, power, duty cycle, repetition frequency, phase difference, and spot movement speed.
5. The three-step polishing method for suppressing high-frequency errors in CO2 laser polishing of fused silica elements according to claim 4, characterized in that: In step S300, during the second high-speed multilayer polishing, the maximum thermodynamic temperature of the surface material of the fused silica element exceeds the melting temperature of 2273K but is lower than the evaporation temperature of 2973K.
6. The three-step polishing method for suppressing high-frequency errors in CO2 laser polishing of fused silica elements according to claim 5, characterized in that: In step S400, the maximum thermodynamic temperature of the surface material in the third step of low-speed single-layer polishing exceeds the maximum thermodynamic temperature of the material during the laser polishing process in step S300, but is lower than the evaporation temperature of the fused silica material, which is 2973K.
7. The three-step polishing method for suppressing high-frequency errors in CO2 laser polishing of fused silica elements according to claim 6, characterized in that: The laser moving speed is greater than 1 mm / s during the second step of high-speed multi-layer polishing, and less than 1 mm / s during the third step of low-speed single-layer polishing.
8. The three-step polishing method for suppressing high-frequency errors in CO2 laser polishing of fused silica elements according to claim 7, characterized in that: The second step, high-speed multi-layer polishing, involves five polishing layers, while the third step, low-speed single-layer polishing, involves one polishing layer.