A processing method for a fused silica component with a smooth surface and a high damage threshold

Abstract

A processing method for a fused silica component with a smooth surface and a high damage threshold, comprising: performing post-treatment polishing on the cutting, milling and forming, plasma deep etching, plasma shallow etching and ion beam polishing of the fused silica blank. In the whole process of the present invention, non-contact processing is adopted. Based on the non-contact plasma etching and ion beam polishing processing techniques, the fused silica blank after precision milling is directly processed in combination to obtain a fused silica component with a smooth surface and a high damage threshold.

Description

Technical Field

[0001] The present invention relates to the manufacture of optical components, and in particular to a processing method for a fused silica component having a smooth surface and a high damage threshold. Background Art

[0002] Fused silica glass has the characteristics of high mechanical strength, low thermal conductivity, low expansion coefficient, high softening temperature, excellent dielectric properties and high transmittance in a very wide spectral range. A large number of high-power laser devices use fused silica components as terminal optical components. With the increase in the flux of high-power laser devices, when a high-energy laser beam irradiates a fused silica component, damage is very likely to occur on the surface of the fused silica component, which will have a destructive impact on the use of the fused silica component, reduce the service life of the component, and the laser damage threshold of the fused silica component limits the overall improvement. At the same time, the surface quality of the fused silica component affects the quality of the high-energy laser beam, and thus affects the system performance of the device. Therefore, it is an urgent problem to be solved to obtain a fused silica component with a smooth surface and a high damage threshold, and thus improve the performance of high-power laser devices.

[0003] Currently, the existing processing means for obtaining fused silica components with a smooth surface and a high damage threshold mainly focus on processes such as precision polishing and post-treatment of components, including chemical mechanical polishing, magnetorheological polishing, ion beam polishing, and hydrofluoric acid treatment. Under chemical mechanical polishing, a smooth surface can be obtained, but the re-deposited layer formed on the surface of the component limits the improvement of the damage threshold. Magnetorheological polishing can obtain a smooth surface without introducing subsurface damage, but iron powder will remain on the surface of the component polished by magnetorheological polishing, which will then affect the damage threshold of the fused silica component. Ion beam polishing is a processing method based on a vacuum environment to achieve atomic-level material removal. After ion beam polishing, the component can obtain a smooth surface and an improved damage threshold, but its processing cost is high and the efficiency is very low, and it is only applicable to the final process of precision polishing. Hydrofluoric acid post-treatment is to remove the re-deposited layer on the surface of the fused silica component and passivate and merge the cracks in the subsurface defects through a chemical reaction. However, hydrofluoric acid has strong corrosiveness and low safety. If the treatment time is too long, the surface shape accuracy of the fused silica component will be damaged, resulting in deterioration of the surface quality. If the treatment time is too short, the residual impurities and subsurface defect cracks cannot be completely removed, and the entire treatment process requires multiple treatments, and the steps are cumbersome and complex. Plasma etching treatment has the characteristics of low cost, non-contact, and no introduction of subsurface damage. Existing patents have introduced methods for using plasma etching to improve the damage threshold of components, but it only targets polished glass, and the previous processes still use traditional physical methods, and the existing subsurface damage has not been completely removed, and the surface topography deterioration caused by plasma etching results in the component not having a smooth surface.

[0004] Based on the above discussion, in the full-process machining flow of fused silica components, how to avoid the re-deposition layer and subsurface defect damage caused by traditional machining methods and obtain fused silica components with a smooth surface and high damage threshold is of great significance for improving the performance of high-power laser devices. Summary of the Invention

[0005] The object of the present invention is to propose a processing method for fused silica components with a smooth surface and high damage threshold.

[0006] The full-process machining process of the present invention is based on non-contact plasma etching and ion beam polishing post-treatment processes, avoiding the re-deposition layer and subsurface damage generated by traditional machining methods, and obtaining fused silica components with a smooth surface and high damage threshold. The present invention has the characteristics of simple operation, safety and reliability, and obtains fused silica components with both a smooth surface and high damage threshold.

[0007] The technical solution of the present invention is as follows:

[0008] A processing method for fused silica components with a smooth surface and high damage threshold, characterized in that the processing method includes:

[0009] A) Blank cutting: Use a wire cutting machine to cut the fused silica blank into the drawing size. Select a cutting wire diameter of 0.125 - 0.25 mm and a cutting speed of 0.1 - 0.5 mm / min;

[0010] B) Milling and forming: According to the milling tolerance required by the drawing, use a CNC optical processing center to mill the cut fused silica to the specified external dimension. The milling process for the machining surface includes rough milling and fine milling, and the milling process for the non-machining surface includes rough milling, where the material removal depth of the rough milling process is d 1 . The material removal depth of the fine milling process is d 2 .

[0011] C) Plasma deep etching: Place the precisely milled and formed fused silica component on the stage of a plasma processing machine tool, and use a tooling fixture to fix the fused silica component. Adjust the etching parameters of the plasma, and use the plasma processing machine tool to perform deep etching on the precisely ground component to completely remove the damage layer on the surface and subsurface of the fused silica component. The material removal depth of the plasma deep etching process is d 3 .

[0012] D) Plasma shallow etching: Place the fused silica component after deep plasma etching on the stage of the plasma processing machine tool, and use a tooling fixture to fix the fused silica component. Adjust the etching parameters of the plasma, and use the plasma processing machine tool to perform shallow etching on the component after deep plasma etching to remove the surface deposits and merge the microstructures on the surface of the component. The material removal depth of the plasma shallow etching process is d 4 .

[0013] E) Ion beam polishing post-treatment: For the fused silica component after plasma shallow etching, use ion beam polishing post-treatment to further remove the contaminants on the surface of the fused silica. The material removal depth of the ion beam polishing post-treatment process is d 5 , and finally obtain a smooth surface with a root mean square roughness better than 1 nm.

[0014] Between the step (B), the step (C), the step (D) and the step (E), the following steps are further included: performing ultrasonic and megasonic cleaning on the fused silica optical component.

[0015] The processing method of a fused silica component with a smooth surface and a high damage threshold is characterized in that: in the ultrasonic and megasonic cleaning of the fused silica component, the cleaning environment is class 100 clean. The cleaning medium is deionized water, and the resistance of the deionized water is ≥15 MΩ. Among them, the ultrasonic frequency is 40 - 200 kHz, the cleaning time is 5 - 10 min, and the cleaning temperature is 40 - 50 °C; the megasonic frequency is 430 kHz - 1 MHz, the cleaning time is 5 - 10 min, and the cleaning temperature is 40 - 50 °C. Finally, dehydrate the component with anhydrous ethanol.

[0016] The processing method of a fused silica component with a smooth surface and a high damage threshold is characterized in that: for the rough milling process of milling and forming, use a diamond grinding wheel with 400 - 600 mesh fixed abrasive grains; for the fine milling process of milling and forming, use a diamond grinding wheel with 800 - 1200 mesh fixed abrasive grains.

[0017] The processing method of a fused silica component with a smooth surface and a high damage threshold is characterized in that: the material removal depth is d 1 and d 2 take values of 100 - 200 μm and 20 - 50 μm respectively; the material removal depth is d 3 and d 4 take values of 10 - 50 μm and 1 - 10 μm respectively; the material removal depth is d 5 is 0.2 - 2 μm.

[0018] A processing method for a fused silica component with a smooth surface and a high damage threshold, characterized in that: the working environment of the plasma is atmospheric pressure, and the radio frequency is 13.56 MHz; the carrier gas used is helium or argon, the reaction gas is carbon tetrafluoride or sulfur hexafluoride, and the auxiliary gas is oxygen; in the deep plasma etching process, the reaction power is 200-500 W, the flow rate of the carrier gas is 1500-4000 ml / min, the flow rate of the reaction gas is 120-200 ml / min, and the flow rate of the auxiliary gas is 20-50 ml / min; in the shallow plasma etching process, the reaction power is 100-200 W, the flow rate of the carrier gas is 500-1500 ml / min, the flow rate of the reaction gas is 50-100 ml / min, and the flow rate of the auxiliary gas is 5-20 ml / min.

[0019] A processing method for a fused silica component with a smooth surface and a high damage threshold, characterized in that: in the deep plasma etching process, the excitation electrode of the plasma is an aluminum electrode, and preferably a layer of alumina ceramic film is plated on the electrode surface. In the shallow plasma etching process, the excitation electrode of the plasma is a graphite electrode. In the shallow plasma etching process, the active particles in the plasma react with the graphite electrode, and the product is carbon dioxide, which further avoids the adsorption and accumulation of reaction products on the surface of the processed component.

[0020] A processing method for a fused silica component with a smooth surface and a high damage threshold, characterized in that: in the deep plasma etching and shallow plasma etching processes, the plasma torch is located 1-3 mm above the fused silica component, and a grating type, spiral type or random path is adopted. The distance between adjacent etching points and the distance between adjacent rows of etching points in the movement path range from 0.5 to 1 mm; in the deep plasma etching process, the equivalent residence time of a single etching point of the fused silica component is 2-10 s, that is, the movement speed of the plasma is 0.1-0.5 mm / s; in the shallow plasma etching process, the equivalent residence time of a single etching point of the fused silica component is 0.1-1 s, that is, the movement speed of the plasma is 1-10 mm / s.

[0021] A processing method for a fused silica component with a smooth surface and a high damage threshold, characterized in that: an ion beam polishing post-treatment process, the ion source used is an argon ion, the ion beam energy is 400-900 eV, the processing distance is 30-50 mm, and the ion beam incident angle is 40-70°.

[0022] The technical effects of the present invention are as follows:

[0023] The whole process of the present invention adopts a non-contact processing method, avoiding the normal positive pressure in the traditional processing method; the plasma directly removes different depths of quartz after precision milling and grinding, completely removing the surface and subsurface damage layers; the plasma uses a graphite electrode for etching, avoiding the deposited layers and pollutants of plasma shallow etching; the post-treatment method of ion beam polishing removes the deposited layers after plasma etching. Brief Description of the Drawings

[0024] Figure 1 is a flow chart of the processing method of the high damage threshold fused silica element of the present invention; Detailed Description of the Invention

[0025] The present invention will be further described below in conjunction with embodiments, but the scope of transformation of the present invention should not be limited thereby.

[0026] Refer to Figure 1 , Figure 1 which is a flow chart of the processing method of the high damage threshold fused silica element of the present invention. It can be seen from the figure that in the embodiment of the present invention, a fused silica element with a size of φ50×5mm is used as the processing object, and the processing method includes the following steps:

[0027] A) Blank cutting: Use a wire cutting machine to cut the fused silica blank into the drawing size. Select a cutting wire diameter of 0.125mm and a cutting speed of 0.2mm / min;

[0028] B) Milling and forming: Use a numerical control milling machine to mill the cut fused silica to the specified outer dimension. The milling process of the processing surface includes rough grinding and fine grinding. First, use a diamond grinding wheel with 600 mesh fixed abrasive grains to remove the material depth of 120 - 150μm; then use a diamond grinding wheel with 1000 mesh fixed abrasive grains to remove the material depth of 30 - 40μm.

[0029] C) Plasma deep etching: Use a plasma processing machine tool to perform deep etching on the precision ground element. The material removal depth of the plasma deep etching process is 25 - 30μm.

[0030] D) Plasma shallow etching: Use a plasma processing machine tool to perform shallow etching on the element after plasma deep etching. The material removal depth is 3 - 6μm.

[0031] E) Ion beam polishing post-treatment: Use ion beam polishing post-treatment, and the material removal depth is 0.5 - 1μm, finally obtaining a smooth surface with a root mean square roughness better than 1nm.

[0032] Between the steps (B), (C), (D) and (E), the following steps are further included: in a hundred-class clean environment, the fused silica optical element is ultrasonically and megasonically cleaned with deionized water having a water resistance of 15 MΩ. The ultrasonic frequencies are 40, 75 and 120 kHz, the cleaning time is 5 - 10 min, and the cleaning temperature is 40 - 50 °C; the megasonic frequencies are 430, 950 MHz, the cleaning time is 5 - 10 min, and the cleaning temperature is 40 - 50 °C. Finally, the element is dehydrated with anhydrous ethanol.

[0033] The excitation environment of the plasma is atmospheric pressure, and the radio frequency is 13.56 MHz; the carrier gas used is helium, the reaction gas is carbon tetrafluoride, the auxiliary gas is oxygen, the plasma torch is located 1 - 2 mm above the fused silica element, a grating path is adopted, and the spacing between adjacent etching points and the spacing between adjacent rows of etching points in the movement path range from 0.5 - 1 mm.

[0034] In the deep plasma etching process, the excitation electrode is an aluminum electrode plated with alumina ceramic, the reaction power is 300 - 400 W, the flow rate of the carrier gas is 2500 - 3500 ml / min, the flow rate of the reaction gas is 150 - 180 ml / min, and the flow rate of the auxiliary gas is 20 - 30 ml / min. The equivalent residence time of a single etching point of the fused silica element is 2 - 5 s, that is, the movement speed of the plasma is 0.2 - 0.5 mm / s.

[0035] In the shallow plasma etching process, the excitation electrode is a graphite electrode, the reaction power is 100 - 150 W, the flow rate of the carrier gas is 800 - 1200 ml / min, the flow rate of the reaction gas is 50 - 80 ml / min, and the flow rate of the auxiliary gas is 5 - 15 ml / min; the equivalent residence time of a single etching point of the fused silica element is 0.1 - 0.5 s, that is, the movement speed of the plasma is 2 - 10 mm / s.

[0036] In the post-treatment process of ion beam polishing, the ion source is argon ion, the ion beam energy is 650 - 750 eV, the processing distance is about 35 - 40 mm, and the ion beam incident angle is 60 - 70°.

[0037] The fused silica element of the present invention is tested for the 1-on-1 laser damage threshold according to the international standard ISO 21254. The test laser wavelength is 355 nm, the pulse width is 8 ns, and the test results show that the damage threshold of the fused silica element before and after plasma processing by the processing method of the present invention with a 0% damage probability is increased from 7.8 J / cm 2 to 28.2 J / cm 2 .

[0038] Experiments show that the entire process flow of the present invention adopts non-contact processing, directly processes the fused silica after precision milling and grinding, uses the method of plasma etching to remove the damaged layers on the surface and subsurface of the fused silica, completely removes the damaged layers on the surface and subsurface of the fused silica, and adopts the ion beam post-treatment method to effectively remove the pollutants on the surface of the fused silica and make the root mean square roughness of the final surface better than 1 nm, obtaining a fused silica component with a smooth surface and a high damage threshold.

[0039] The present invention has the characteristics of simple operation, safety and reliability. The entire process adopts a non-contact processing method, directly conducts combined processing on the precision ground fused silica blank, and obtains a fused silica component with a smooth surface and a high damage threshold based on the plasma etching at different depths and the post-treatment process of coupling ion beam polishing.

Claims

1. A processing method for a fused silica component with a smooth surface and a high damage threshold, characterized in that, the processing method includes: A) Blank cutting: Use a wire cutting machine to cut the fused silica blank into the drawing size, and select a cutting wire diameter of 0.125 - 0.25 mm and a cutting speed of 0.1 - 0.5 mm / min; B) Milling and grinding to form: According to the milling tolerance required by the drawing, use a numerical control optical processing center to mill and grind the cut fused silica to the specified outer dimension; The milling and grinding process of the machined surface includes rough milling and grinding and finish milling and grinding. The milling and grinding process of the non-machined surface includes rough milling and grinding, where the material removal depth of the rough milling and grinding process is d 1 , and the material removal depth of the finish milling and grinding process is d 2 ; C) Plasma deep etching: Place the fused silica component after precision milling on the stage of the plasma processing machine tool, and use a tooling fixture to fix the fused silica component; adjust the etching parameters of the plasma, and use the plasma processing machine tool to perform deep etching on the component after precision grinding to completely remove the damaged layer on the surface and subsurface of the fused silica component. The material removal depth of the plasma deep etching process is d 3 ; D) Plasma shallow etching: Place the fused silica component after deep plasma etching on the stage of the plasma processing machine tool, and fix the fused silica component with a tooling fixture; adjust the etching parameters of the plasma, and use the plasma processing machine tool to perform shallow etching on the component after deep plasma etching to remove the surface deposits and merge the microstructures on the component surface. The material removal depth of the plasma shallow etching process is d 4 ; E) Post-treatment by ion beam polishing: For the fused silica component after plasma shallow etching, post-treatment by ion beam polishing is used to remove the contaminants on the surface of the fused silica. The material removal depth of the ion beam polishing post-treatment process is d 5 , and finally a smooth surface with a root mean square roughness better than 1 nm is obtained.

2. The processing method for a fused silica component with a smooth surface and a high damage threshold according to claim 1, characterized in that: Between step (B), step (C), step (D) and step (E), the following step is further included: performing ultrasonic and megasonic cleaning on the fused silica optical component.

3. The processing method for a fused silica component with a smooth surface and a high damage threshold according to claim 2, characterized in that: In the ultrasonic and megasonic cleaning of the fused silica component, the cleaning environment is class 100 clean, the cleaning medium is deionized water, the resistance of the deionized water is ≥ 15 MΩ, wherein the ultrasonic frequency is 40 - 200 kHz, the cleaning time is 5 - 10 min, and the cleaning temperature is 40 - 50 °C; the megasonic frequency is 430 kHz - 1 MHz, the cleaning time is 5 - 10 min, and the cleaning temperature is 40 - 50 °C. Finally, dehydrate the component with anhydrous ethanol.

4. The processing method for a fused silica component with a smooth surface and a high damage threshold according to claim 1, characterized in that: For the rough milling process of milling and grinding to form, use a diamond grinding wheel with fixed abrasive grains of 400 - 600 mesh; for the fine grinding process of milling and grinding to form, use a diamond grinding wheel with fixed abrasive grains of 800 - 1200 mesh.

5. The processing method for a fused silica component with a smooth surface and a high damage threshold according to claim 1, characterized in that: The material removal depth is d 1 and d 2 take values of 100 - 200 μm and 20 - 50 μm respectively; the material removal depth is d 3 and d 4 take values of 10 - 50 μm and 1 - 10 μm respectively; the material removal depth is d 5 is 0.2 - 2 μm.

6. The processing method for a fused silica component with a smooth surface and a high damage threshold according to claim 1, characterized in that: The working environment of the plasma is atmospheric pressure, and the radio frequency is 13.56 MHz; the carrier gas used is helium or argon, the reaction gas is carbon tetrafluoride or sulfur hexafluoride, and the auxiliary gas is oxygen; wherein in the plasma deep etching process, the reaction power is 200 - 500 W, the flow rate of the carrier gas is 1500 - 4000 ml / min, the flow rate of the reaction gas is 120 - 200 ml / min, and the flow rate of the auxiliary gas is 20 - 50 ml / min; wherein in the plasma shallow etching process, the reaction power is 100 - 200 W, the flow rate of the carrier gas is 500 - 1500 ml / min, the flow rate of the reaction gas is 50 - 100 ml / min, and the flow rate of the auxiliary gas is 5 - 20 ml / min.

7. The processing method for a fused silica component with a smooth surface and a high damage threshold according to claim 1, characterized in that: In the plasma deep etching process, the excitation electrode of the plasma is an aluminum electrode; in the plasma shallow etching process, the excitation electrode of the plasma is a graphite electrode.

8. A processing method of a fused silica element with a smooth surface and a high damage threshold, according to claim 7, characterized in that: a layer of alumina ceramic film is plated on the surface of the aluminum electrode.

9. A processing method of a fused silica element with a smooth surface and a high damage threshold, according to claim 1, characterized in that: in the plasma deep etching and plasma shallow etching processes, the plasma torch is located 1-3 mm above the fused silica element, and a grating type, spiral type or random path is adopted. The distance between adjacent etching points in the movement path and the distance between adjacent rows of etching points range from 0.5 to 1 mm; in the plasma deep etching process, the equivalent residence time of a single etching point of the fused silica element is 2 to 10 s, that is, the movement speed of the plasma is 0.1 to 0.5 mm / s; in the plasma shallow etching process, the equivalent residence time of a single etching point of the fused silica element is 0.1 to 1 s, that is, the movement speed of the plasma is 1 to 10 mm / s.

10. A processing method of a fused silica element with a smooth surface and a high damage threshold, according to claim 1, characterized in that: for the post-treatment process of ion beam polishing, the ion source used is argon ion, the ion beam energy is 400-900 eV, the processing distance is 30-50 mm, and the ion beam incident angle is 40-70°.

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