A method for optimizing the CO2 laser polishing speed of fused silica components based on the uniform distribution of imaginary temperature

Abstract

The present invention provides a method for optimizing the CO2 laser polishing speed of fused silica components based on the uniform distribution of the imaginary temperature, belonging to the technical field of optical processing. In order to solve the problems in the existing CO2 laser polishing process of fused silica components, the unevenly distributed imaginary temperature and residual stress caused by heat accumulation will affect the transmission of the optical path, cause large deformation of the components, and even generate surface cracks, seriously affecting the engineering application of this process. Based on the corresponding relationship between the imaginary temperature distribution and the residual stress distribution, the present invention obtains the two-dimensional distribution of the imaginary temperature inside the fused silica component after CO2 laser polishing through finite element simulation, optimizes the instantaneous speed during the polishing process to achieve a uniform distribution of the imaginary temperature inside the component, and then obtains a fused silica component with a uniform residual stress distribution, preventing surface deformation and the generation of surface cracks of the component, thereby providing theoretical guidance and optimization methods for the engineering application of the CO2 laser polishing process of fused silica components.

Description

Technical Field

[0001] The present invention relates to the technical field of optical processing, and more particularly, to a method for optimizing the CO2 laser polishing speed of fused silica components based on the assumption of uniform temperature distribution. Background Art

[0002] Fused silica material is a typical hard and brittle material. Due to its excellent mechanical and chemical properties and good light transmittance, it is widely used in high-power solid laser devices. Since fused silica material has a high energy absorption rate for 10.6 μm wavelength laser (CO2 laser), the processing method of CO2 laser processing of fused silica components has received extensive attention. When CO2 laser irradiates fused silica material, the material absorbs laser energy, the temperature rises and gradually melts into a liquid state, and the pit defects on the surface of the component are gradually filled under the action of the surface tension of the fluid, so as to obtain a fused silica component with a defect-free surface and low roughness.

[0003] At present, there are a series of problems in the process of CO2 laser polishing of fused silica components. During the process of the temperature rise of fused silica material, the microstructure inside the material changes, that is, material modification occurs. The TOOL uses the fictitious temperature T f (Fictivetemperature) to characterize this structure transformation and material modification phenomenon. During the whole process of heating temperature rise and cooling of fused silica material, its initial fictitious temperature is about 1315K. When the material temperature is lower than the glass transition temperature Tg (Glass transition), the structural relaxation time of the material, that is, the time required for the internal microstructure of the material to transform to the internal microstructure corresponding to the thermodynamic temperature is extremely long, and the fictitious temperature remains unchanged; when the material temperature exceeds Tg, the structural relaxation time of the material rapidly decreases, and the internal microstructure rearranges to reach equilibrium, and the fictitious temperature gradually becomes consistent with the thermodynamic temperature. When the material cools, when the structural relaxation of the material cannot keep up with the rate of decrease of the thermodynamic temperature, the freezing of the internal structure of the material will occur, and the fictitious temperature deviates from the thermodynamic temperature and freezes at a certain higher temperature, that is, the "freezing temperature". The increase in fictitious temperature will lead to a linear increase in material density, causing the material surface to deform and generate residual stress. According to the research of domestic and foreign scholars, there is a certain relationship between the distribution of fictitious temperature and the distribution of residual stress. A uniformly distributed fictitious temperature field can generate a uniformly distributed residual stress field and can greatly improve the laser damage threshold of fused silica components. However, in the process of CO2 laser polishing of fused silica components, due to heat accumulation, the unevenly distributed fictitious temperature and residual stress will affect the transmission of the optical path, cause large deformation of the component, and even generate surface cracks, seriously affecting the engineering application of this process. Summary of the Invention

[0004] The technical problem to be solved by the present invention is:

[0005] In order to solve the problem that in the existing CO2 laser polishing process of fused silica components, the imaginary temperature and residual stress caused by heat accumulation and uneven distribution will affect the transmission of the optical path, cause large deformation of the components, and even produce surface cracks, seriously affecting the engineering application of this process.

[0006] The technical solution adopted by the present invention to solve the above technical problems:

[0007] The present invention provides a method for optimizing the CO2 laser polishing speed of fused silica components based on the uniform distribution of imaginary temperature, including the following steps:

[0008] Step 1: Obtain the imaginary temperature distribution after cooling of the fused silica component through finite element simulation according to the evolution of the thermodynamic temperature field.

[0009] Step 2: Extract the modified layer boundary curve between the modified layer and the fused silica matrix according to the imaginary temperature distribution in Step 1, extract the depth of the modified layer boundary curve along the horizontal direction of the fused silica component, and integrate the depths of the modified layer boundary curves at different horizontal positions to obtain the fitting curve of the modified layer boundary depth.

[0010] Step 3: Analyze the fitting curve of the modified layer boundary depth, take the depth value corresponding to the horizontal position in the middle region as the ideal depth of the modified layer, use the proportional optimization method to optimize and solve the laser moving speed for the horizontal positions with non-ideal depths of the modified layer, obtain the fitting curve of the relationship between the optimized speed and the horizontal position, and control the moving speed of the laser during laser polishing according to the fitting curve of the relationship between the optimized speed and the horizontal position to achieve variable-speed laser polishing of the fused silica component.

[0011] Step 4: Repeat Step 1 for the polished fused silica component in Step 3. If the obtained imaginary temperature distribution is still uneven along the horizontal direction, repeat Step 2, Step 3, and Step 1 in sequence until the obtained imaginary temperature distribution is uniform along the horizontal direction.

[0012] Furthermore, in Step 1, the imaginary temperature distribution can be solved and calculated by using the thermodynamic temperature field distribution through the ordinary differential equation of material structure relaxation. The ordinary differential equation is:

[0013]

[0014]

[0015] In the above formula,

[0016] T — Thermodynamic temperature (K);

[0017] T f — Imaginary temperature (K);

[0018] τ0—the relaxation time constant (s);

[0019] R—the ideal gas constant;

[0020] ΔH—the activation energy (KJ / mol);

[0021] η—the distribution coefficient between the thermodynamic temperature and the imaginary temperature.

[0022] Further, in step three, the ratio optimization method is as follows:

[0023] Calculate the optimized speed corresponding to each horizontal position using the following formula,

[0024]

[0025] In the above formula,

[0026] x i —the horizontal position of the i-th point;

[0027] v xi —the optimized speed of the i-th point;

[0028] v ave —the speed of uniform polishing before optimization;

[0029] y xi —the depth of the modified layer at the i-th point;

[0030] y ave —the ideal depth of the modified layer;

[0031] α—the amplification factor;

[0032] Integrate the optimized speeds corresponding to each obtained horizontal position to obtain the fitting curve of the relationship between the optimized speed and the horizontal position.

[0033] Further, in step four, the method for judging whether the imaginary temperature distribution is uniform along the horizontal direction is as follows:

[0034] Analyze the depth curve of the modified layer optimized through steps one to three, calculate the relative ideal depth and the peak-valley difference of the relative ideal depth with respect to the relative ideal depth. If the difference in the relative ideal depth is less than or equal to 10%, then the optimized imaginary temperature distribution is uniform along the horizontal direction. If the difference in the relative ideal depth is greater than 10%, then the optimized imaginary temperature distribution is non-uniform along the horizontal direction; if the peak-valley difference in the relative ideal depth is less than or equal to 15%, then the optimized imaginary temperature distribution is uniform along the horizontal direction. If the peak-valley difference in the relative ideal depth is greater than 15%, then the optimized imaginary temperature distribution is non-uniform along the horizontal direction.

[0035] Further, the modified layer depth curves in the boundary regions on both sides of the fused silica element are selected for analysis.

[0036] Further, the width of the boundary regions on both sides is 1 / 4 - 3 / 8 of the overall width of the fused silica element.

[0037] Further, in step one, the hypothetical temperature distribution after cooling is the hypothetical temperature distribution when the maximum thermodynamic temperature of the element drops to room temperature.

[0038] Further, the initial set value of the amplification factor is 1.

[0039] Further, the parameter settings for the finite element simulation calculation include the spot radius, laser power, laser moving speed, and moving distance.

[0040] Further, in the laser variable speed polishing in step three, the spot radius, laser power, and moving distance are the same as those used in the finite element simulation calculation.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] (1) Currently, there are laser devices that can achieve variable speed movement, and the laser moving speed can be adjusted in real time through a program. Applying the fitting curve of the optimized speed and horizontal position relationship determined by this solution to the laser device that can achieve variable speed movement can realize the optimized processing of the fused silica element. Therefore, this speed optimization method is beneficial for practical engineering applications.

[0043] (2) This method has iterability. By gradually optimizing, the hypothetical temperature distribution can be approximated to a uniform distribution state, and finally an ideal element with a uniform surface residual stress distribution can be obtained. The hypothetical temperature and residual stress of the ideal element are uniform, which will not affect the optical path transmission or cause large deformation or surface cracks in the element.

[0044] (3) Using the uniform distribution of the hypothetical temperature as the optimization target, since it is difficult to measure the surface residual stress distribution of the processed fused silica element, and from the simulation results, the residual stress distribution is complex and there is no obvious pattern, it is very difficult to use the residual stress as the optimization target to optimize the processing parameters. Compared with directly using the uniform distribution of the residual stress as the optimization target, this method reduces the complexity of the optimization process and provides an optimization method for the engineering application of the CO2 laser polishing fused silica element process. Description of the Drawings

[0045] Figure 1 It is a schematic diagram of the modified layer boundary in the embodiment of the present invention;

[0046] Figure 2 It is a schematic diagram of the laser polishing process in the embodiment of the present invention;

[0047] Figure 3 This is the hypothetical temperature distribution diagram inside the fused silica component before optimization calculated in the embodiment of the present invention;

[0048] Figure 4 This is the depth curve diagram of the modified layer before optimization in the embodiment of the present invention;

[0049] Figure 5 This is the fitting curve diagram of the relationship between the optimization speed and the horizontal position in the embodiment of the present invention;

[0050] Figure 6 This is the hypothetical temperature distribution diagram inside the optimized component obtained with a magnification factor of 0.8 in the embodiment of the present invention;

[0051] Figure 7 This is the comparison diagram of the depth of the modified layer near the left and right boundaries before and after optimization with a magnification factor of 0.8 in the embodiment of the present invention. Detailed implementation manners

[0052] In the description of the present invention, it should be noted that the term nouns in each embodiment, such as "upper", "lower", "front", "rear", "left", "right", etc., which indicate directions, are only used to simplify the description of the positional relationship based on the drawings of the specification, and do not represent that the indicated components and devices, etc., must be operated according to the specific directions, limited operations and methods, and structures in the specification. Such direction nouns do not constitute a limitation to the present invention.

[0053] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be given with reference to the drawings.

[0054] Specific implementation manner one: Combining Figure 1 As shown, the present invention provides a method for optimizing the CO2 laser polishing speed of a fused silica component based on a uniform distribution of hypothetical temperature, including the following steps:

[0055] Step 1. Obtain the hypothetical temperature distribution after cooling for the cooled fused silica component through finite element simulation according to the evolution of the thermodynamic temperature field; the evolution of the thermodynamic temperature field is the actual temperature evolution calculated by finite element simulation, and the hypothetical temperature can be obtained from an ordinary differential equation containing the thermodynamic temperature. The hypothetical temperature distribution after cooling is the hypothetical temperature distribution when the maximum thermodynamic temperature of the component drops to room temperature (293.15K). The ordinary differential equation is:

[0056]

[0057]

[0058] In the above formula,

[0059] T — Thermodynamic temperature (K);

[0060] T f — Hypothetical temperature (K);

[0061] τ0 — Relaxation time constant (s), with a value of 1.064×10 -17 (s);

[0062] R — Ideal gas constant, with a value of 8.314 (J / (mol·K));

[0063] ΔH — Activation energy (KJ / mol), with a value of 542 (KJ / mol);

[0064] η — Distribution coefficient between thermodynamic temperature and hypothetical temperature, with a value of 0.9.

[0065] The software used for the finite element simulation is COMSOL commercial software, and the specific steps are as follows:

[0066] 1. Establish a multi-physics coupling model including a heat transfer module, a fluid flow module, a structural relaxation module (i.e., the ordinary differential equation of thermodynamic temperature and hypothetical temperature), and a laser variable speed movement module;

[0067] 2. Supplement relevant parameters into the model;

[0068] 3. Perform mesh division and transient study settings on the model;

[0069] 4. Run the simulation software and export the distribution of the hypothetical temperature at the result.

[0070] Step 2: Extract the modified layer boundary curve between the modified layer and the fused silica substrate according to the hypothetical temperature distribution in Step 1, extract the depth of the modified layer boundary curve along the horizontal direction of the fused silica element, and integrate the depths of the modified layer boundary curves at different horizontal positions to obtain the modified layer boundary depth fitting curve;

[0071] The modified layer boundary curve is the boundary line between the region where the hypothetical temperature in the fused silica element has not changed and the region where it has changed. Above the boundary line, due to the increase in thermodynamic temperature, the hypothetical temperature changes and the material is modified, i.e., the modified layer; below the boundary line, due to the extremely long structural relaxation time of the material, the hypothetical temperature of the material remains constant, i.e., the fused silica substrate; the depth of the modified layer boundary curve along the horizontal direction of the fused silica element is the vertical distance from the surface of the fused silica element to the modified layer boundary curve. A schematic diagram of the material modified layer boundary after CO2 laser polishing is as Figure 1 shown.

[0072] Step 3: Analyze the fitting curve of the modified layer boundary depth, and take the depth value corresponding to the horizontal position in the middle area as the ideal depth of the modified layer. For the horizontal position of the ideal depth of the non-modified layer, use the proportional optimization method to optimize and solve the laser moving speed, obtain the fitting curve of the relationship between the optimized speed and the horizontal position, and control the moving speed of the laser during laser polishing according to the fitting curve of the relationship between the optimized speed and the horizontal position, so as to realize the variable-speed laser polishing of fused silica components;

[0073] The proportional optimization method is as follows:

[0074] Calculate the optimized speed corresponding to each horizontal position using the following formula

[0075]

[0076] In the above formula,

[0077] x i — The horizontal position of the i-th point;

[0078] v xi — The optimized speed of the i-th point;

[0079] v ave — The speed of uniform polishing before optimization;

[0080] y xi — The depth of the modified layer at the i-th point;

[0081] y ave — The ideal depth of the modified layer;

[0082] α — The amplification factor, with an initial setting value of 1;

[0083] Integrate the optimized speeds corresponding to each obtained horizontal position, so as to obtain the fitting curve of the relationship between the optimized speed and the horizontal position.

[0084] Step 4: Repeat Step 1 for the polished fused silica component in Step 3. If the obtained imaginary temperature distribution is still uneven along the horizontal direction, repeat Step 2, Step 3, and Step 1 in sequence until the obtained imaginary temperature distribution is uniform along the horizontal direction;

[0085] The method for judging whether the imaginary temperature distribution is uniform along the horizontal direction is as follows:

[0086] Analyze the modified layer depth curve optimized through steps 1 to 3, calculate the relative ideal depth and the peak-to-valley difference of the relative ideal depth. The relative ideal depth is the maximum difference between the modified layer depth and the ideal depth of the modified layer divided by the ideal depth. The peak-to-valley difference of the relative ideal depth is the peak-to-valley difference divided by the ideal depth. If the difference of the relative ideal depth is less than or equal to 10%, the optimized imaginary temperature distribution is uniform along the horizontal direction. If the difference of the relative ideal depth is greater than 10%, the optimized imaginary temperature distribution is non-uniform along the horizontal direction. If the peak-to-valley difference of the relative ideal depth is less than or equal to 15%, the optimized imaginary temperature distribution is uniform along the horizontal direction. If the peak-to-valley difference of the relative ideal depth is greater than 15%, the optimized imaginary temperature distribution is non-uniform along the horizontal direction.

[0087] When comparing the optimized modified layer boundary depth fitting curve after extraction with the modified layer boundary depth fitting curve before optimization, observe the changes in the modified layer depth curve before and after optimization, including the maximum difference between the modified layer depth in the left and right boundary regions and the ideal depth of the modified layer and the difference between the peak and valley of the entire modified layer boundary depth fitting curve. The decrease in the difference indicates that the optimized imaginary temperature distribution is more uniform. The magnification factor can be used as a variable to adjust the optimization degree. If the optimization result is not ideal, the optimization can be re-performed by adjusting the magnification factor. The re-optimization is to use the optimized modified layer boundary depth fitting curve as the modified layer depth fitting curve before step 2 for re-optimization to obtain a more uniform imaginary temperature field.

[0088] Preferably, analyze the modified layer depth curves in the boundary regions on both sides of the fused silica element.

[0089] Preferably, the width of the boundary regions on both sides is 1 / 4 - 3 / 8 of the overall width of the fused silica element.

[0090] Preferably, the parameter settings used in the finite element simulation method calculation include the spot radius, laser power, laser moving speed, and moving distance.

[0091] Preferably, in the laser variable-speed polishing in step 3, the spot radius, laser power, and moving distance are the same as those used in the finite element simulation method calculation.

[0092] Currently, there are laser devices that can achieve variable-speed movement, and the laser moving speed can be adjusted in real time through a program. Apply the optimized speed and horizontal position relationship fitting curve determined by this solution to the laser device that can achieve variable-speed movement to realize the optimization process of the fused silica element. Therefore, this speed optimization method is conducive to practical engineering applications.

[0093] This method is iterative. By gradually optimizing, the imaginary temperature distribution can be made to approach a uniform distribution state, and finally an ideal component with a uniform surface residual stress distribution can be obtained. The imaginary temperature and residual stress of the ideal component are uniform, which will not affect the optical path transmission or cause large deformation or surface cracks in the component.

[0094] Taking the uniform distribution of the imaginary temperature as the optimization goal, since it is difficult to measure the surface residual stress distribution of the processed fused silica component, from the simulation results, the residual stress distribution is complex and there is no obvious pattern. It is very difficult to use the residual stress as the optimization goal to optimize the processing parameters. Compared with directly taking the uniform distribution of the residual stress as the optimization goal, this method reduces the complexity of the optimization process and provides an optimization method for the engineering application of the CO2 laser polishing of fused silica components.

[0095] Specific implementation method two: Combined with Figures 2 to 7 As shown, a method for optimizing the CO2 laser polishing speed of a fused silica component based on the uniform distribution of the imaginary temperature optimizes the speed of the uniformly moving laser polishing according to the above process.

[0096] 1) Parameter setting and finite element simulation calculation of the imaginary temperature distribution

[0097] The laser parameters used in the finite element simulation calculation are shown in Table 1. The laser source is incident from 1 mm away from the left boundary of the fused silica component and moves uniformly to the right. The laser is turned off when it reaches 1 mm away from the right boundary of the fused silica component, as Figure 2 shown, and the fused silica component is given sufficient cooling time, that is, cooled to room temperature; the fused silica component used is a Corning 7980 fused silica component;

[0098] Among them, the distance between the laser source when it enters and exits and the fused silica component is greater than or equal to the spot radius;

[0099]

[0100] Table 1 Table of parameters for uniformly moving laser polishing

[0101] The above parameters are not fixed and can be determined according to the actual situation of the fused silica component. Specifically: the parameters used need to ensure that the surface of the component undergoes melting polishing rather than evaporation removal during the laser polishing process, that is, the surface temperature of the fused silica component should be controlled above the melting temperature (2273 K) and below the vaporization temperature (2973 K).

[0102] The imaginary temperature distribution can be solved and calculated by using the thermodynamic temperature field distribution and the ordinary differential equation of material structure relaxation:

[0103]

[0104]

[0105] In the above formula,

[0106] T — thermodynamic temperature (K);

[0107] T f — fictitious temperature (K);

[0108] τ0 — relaxation time constant (s), with a value of 1.064×10 -17 (s);

[0109] R — universal gas constant, with a value of 8.314 (J / (mol·K));

[0110] ΔH — activation energy (KJ / mol), with a value of 542 (KJ / mol);

[0111] η — distribution coefficient between thermodynamic temperature and fictitious temperature, with a value of 0.9.

[0112] The calculated fictitious temperature distribution inside the fused silica component after cooling is as Figure 3 shown, where the dark area is the surface modified area, and the fictitious temperature in this area increases; the light area is the surface unmodified area, and the fictitious temperature in this area remains unchanged.

[0113] 2) Plot the fitting curve of the modified layer boundary depth

[0114] According to the fictitious temperature distribution obtained from the previous simulation, extract the depth of the modified layer boundary curve in the horizontal direction, and fit to obtain the fitting curve of the modified layer boundary depth and use it as the basis for velocity optimization, as Figure 4 shown;

[0115] Since the depth of the modified layer in the middle region is almost unchanged, this depth (-256μm) is set as the ideal depth of the modified layer, that is, y ave , as Figure 4 shown by the black dashed line in.

[0116] 3) Optimize and solve the laser moving speed

[0117] Using the fitting curve of the modified layer boundary depth obtained in the previous step, combined with the velocity optimization method described in step three, solve the optimized velocity for each horizontal position one by one. By adjusting the amplification factor through multiple calculations, the final determined amplification factor is 0.8. At this time, the solved velocity optimization curve and the morphology of the modified layer depth curve are basically the same as observed by the naked eye, as Figure 5 shown.

[0118] The amplification factor can be used as a variable to adjust the optimization degree. If the optimization result is not ideal, the optimization can be restarted by adjusting the amplification factor.

[0119] 4) Analysis of optimized speed results

[0120] Using the fitting curve of the optimized speed and the horizontal position relationship obtained by optimization, a finite element simulation of the variable-speed laser polishing process of fused silica components is carried out. Except for the speed parameter, the other parameters are the same as those before optimization; the calculated imaginary temperature distribution inside the component after optimization is as Figure 6 shown, and it can be observed that the imaginary temperature distribution at the left and right boundary positions of the component is more uniform compared with the Figure 4 imaginary temperature distribution diagram before optimization;

[0121] The specific steps are as follows: Extract the modified layer depths in the left and right boundary regions of the fused silica component before and after optimization, and compare the fitted modified layer boundary curves, as Figure 7 shown. Taking the maximum difference between the modified layer depth and the ideal modified layer depth as the evaluation criterion, the maximum difference in the left boundary region is reduced from 65 μm to 11 μm after optimization. Relative to the ideal modified layer depth, the relative maximum difference (i.e., the maximum difference divided by the ideal modified layer depth) is reduced from 25.4% to 4.3%; the maximum difference in the right boundary region is reduced from 101 μm to 10 μm after optimization. Relative to the ideal modified layer depth, the relative maximum difference is reduced from 39.5% to 3.9%;

[0122] Taking the maximum height (the difference between the maximum value and the minimum value) of the maximum height difference contour of the modified layer boundary depth fitting curve as the evaluation criterion, the maximum height of the modified layer height difference contour in the left boundary region is reduced from 65 μm to 31 μm after optimization, and the peak-to-valley difference relative to the ideal depth is 12.1%. The maximum height of the modified layer height difference contour in the right boundary region is reduced from 101 μm to 10 μm after optimization, and the peak-to-valley difference relative to the ideal depth is 3.9%. It can be seen that the optimization effect of this method is obvious, and it can make the imaginary temperature distribution more uniform.

[0123] Among them, a two-dimensional rectangular coordinate system is established with the center of the upper surface of the fused silica component as the origin. The left boundary region is the region from (-4000, 0) to (-1000, 0), and the right boundary region is the region from (2000, 0) to (4000, 0).

[0124] Since the imaginary temperature change in the left and right boundary regions of the polished fused silica component is more obvious than that in the middle region, and the modified layer depth in the middle region is close to the ideal modified layer depth, the left and right boundary regions are selected for comparison.

[0125] The above steps use the speed optimization method of the present invention to obtain a more uniform modified layer and imaginary temperature from the numerical simulation results, that is, a more uniform residual stress is obtained, which proves that this method can provide an important theoretical method for the optimization of the CO2 laser polishing process speed of fused silica components.

[0126] Although the present invention is disclosed as above, the scope of protection of the present invention is not limited thereto. Those skilled in the art of the present invention can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will all fall within the scope of protection of the present invention.

Claims

1. A method for optimizing the CO2 laser polishing speed of fused silica components based on the uniform distribution of imaginary temperature, characterized in that, It includes the following steps: Step 1: Obtain the cooled imaginary temperature distribution of the fused silica component according to the evolution of the thermodynamic temperature field through finite element simulation; Step 2: Extract the modified layer boundary curve between the modified layer and the fused silica matrix according to the imaginary temperature distribution in Step 1, extract the depth of the modified layer boundary curve along the horizontal direction of the fused silica component, and integrate the depths of the modified layer boundary curves at different horizontal positions to obtain the fitted curve of the modified layer boundary depth; Step 3: Analyze the fitted curve of the modified layer boundary depth, take the depth value corresponding to the horizontal position in the middle region as the ideal depth of the modified layer, use the proportional optimization method to optimize and solve the laser moving speed for the horizontal positions with non-ideal depths of the modified layer, obtain the fitted curve of the relationship between the optimized speed and the horizontal position, and control the moving speed of the laser during laser polishing according to the fitted curve of the relationship between the optimized speed and the horizontal position to achieve variable-speed laser polishing of the fused silica component; Step 4: Repeat Step 1 for the polished fused silica component in Step 3. If the obtained imaginary temperature distribution is still unevenly distributed along the horizontal direction, repeat Step 2, Step 3, and Step 1 in sequence until the obtained imaginary temperature distribution is evenly distributed along the horizontal direction.

2. The CO2 laser polishing speed optimization method for fused silica components based on the assumed uniform distribution of imaginary temperature according to claim 1, wherein In Step 1, the imaginary temperature distribution can be solved and calculated by using the thermodynamic temperature field distribution through the ordinary differential equation of material structure relaxation. The ordinary differential equation is: In the above formula, T—Thermodynamic temperature; T f — Hypothetical temperature; τ0—Relaxation time constant; R—Ideal gas constant; ΔH—Activation energy; η—the distribution coefficient between the thermodynamic temperature and the imaginary temperature.

3. The method for optimizing the CO2 laser polishing speed of a fused silica element based on the uniform distribution of imaginary temperature according to claim 2, wherein In Step 3, the proportional optimization method is: Calculate the optimized speed corresponding to each horizontal position by using the following formula: In the above formula, xi—the horizontal position of the i-th point; v xi — The optimized speed of the i-th point; v ave — The speed of uniform polishing before optimization; y xi — depth of the i-th point modification layer; y ave — Desired depth of the modified layer; α—Magnification coefficient; Integrate the optimized speeds corresponding to each obtained horizontal position to obtain the fitted curve of the relationship between the optimized speed and the horizontal position.

4. A method for optimizing the CO2 laser polishing speed of fused silica components based on the uniform distribution of imaginary temperature, as claimed in claim 3, wherein In Step 4, the method for judging whether the imaginary temperature distribution is evenly distributed along the horizontal direction is: Analyze the modified layer depth curve optimized through Step 1 to Step 3, calculate the relative ideal depth and the peak-to-valley difference of the relative ideal depth. If the difference of the relative ideal depth is less than or equal to 10%, the optimized imaginary temperature distribution is evenly distributed along the horizontal direction. If the difference of the relative ideal depth is greater than 10%, the optimized imaginary temperature distribution is unevenly distributed along the horizontal direction; if the peak-to-valley difference of the relative ideal depth is less than or equal to 15%, the optimized imaginary temperature distribution is evenly distributed along the horizontal direction. If the peak-to-valley difference of the relative ideal depth is greater than 15%, the optimized imaginary temperature distribution is unevenly distributed along the horizontal direction.

5. A method for optimizing the CO2 laser polishing speed of fused silica components based on the uniform distribution of imaginary temperature, as claimed in claim 4, wherein: Select the modified layer depth curves in the boundary regions on both sides of the fused silica component for analysis.

6. The optimized method for the CO2 laser polishing speed of fused silica components based on the assumed uniform distribution of temperature, as claimed in claim 5, is characterized in that: The width of the boundary regions on both sides is 1 / 4 - 3 / 8 of the overall width of the fused silica component.

7. A method for optimizing the CO2 laser polishing speed of fused silica components based on the assumed uniform distribution of temperature, characterized in that: In Step 1, the cooled imaginary temperature distribution is the imaginary temperature distribution when the maximum thermodynamic temperature of the component drops to room temperature.

8. An optimization method for the CO2 laser polishing speed of fused silica components based on the assumed uniform distribution of imaginary temperature, characterized in that: The initial set value of the magnification coefficient is 1.

9. The method for optimizing the CO2 laser polishing speed of fused silica components based on the uniform distribution of imaginary temperature according to claim 8, characterized in that: The parameter settings for the finite element simulation calculation include spot radius, laser power, laser moving speed, and moving distance.

10. A method for optimizing the CO2 laser polishing speed of fused silica components based on the assumed uniform distribution of imaginary temperature, characterized in that: In the laser variable-speed polishing in Step 3, the spot radius, laser power, and moving distance are the same as those used in the finite element simulation calculation.

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