Processing method of fused quartz element with smooth surface and high damage thresholdTechnical Field
The invention relates to optical element manufacture, in particular to a processing method of a fused quartz element with a smooth surface and a high damage threshold.
Background
The fused silica glass has the characteristics of high mechanical strength, low thermal conductivity, low expansion coefficient, high softening temperature, excellent dielectric property and high permeability in an extremely wide spectral range. High power laser devices use a large number of fused silica components as the terminal optical components. Along with the flux improvement of the high-power laser device, when the high-energy laser beam irradiates the fused quartz element, the surface of the fused quartz element is very easy to damage, so that destructive influence is caused on the use of the fused quartz element, the service life of the element is reduced, and the laser damage threshold of the fused quartz element limits the whole improvement. Meanwhile, the surface quality of the fused quartz element influences the quality of the high-energy laser beam, and further influences the system performance of the device. Thus, obtaining a fused silica component with a smooth surface and a high damage threshold, thereby improving the performance of a high power laser device, is an urgent problem to be solved.
At present, the existing processing means for obtaining the fused quartz component with smooth surface and high damage threshold mainly concentrate on the working procedures of precise polishing, post-treatment and the like of the component, including chemical mechanical polishing, magnetorheological polishing, ion beam polishing, hydrofluoric acid treatment and the like. Smooth surfaces can be achieved under chemical mechanical polishing, but redeposited layers formed on the surface of the element limit the increase in damage threshold. The magnetorheological polishing can obtain a smooth surface without introducing subsurface damage, but the surface of the element subjected to the magnetorheological polishing can remain iron powder, so that the damage threshold of the fused quartz element is affected. Ion beam polishing is a processing mode for removing atomic-level materials based on a vacuum environment, and the element polished by the ion beam can obtain a smooth surface and improve the damage threshold, but has high processing cost and very low efficiency, and is only suitable for a final process of precise polishing. The hydrofluoric acid post-treatment is to remove the redeposited layer on the surface of the fused quartz element and passivate cracks in the combined subsurface defects through chemical reaction, but the hydrofluoric acid has strong corrosiveness and low safety. The surface shape precision of the fused quartz element can be damaged due to overlong treatment time, so that the surface quality is deteriorated, the treatment time is too short, residual impurities and subsurface defect cracks can not be completely removed, the whole treatment process needs multiple treatments, and the steps are complicated. The plasma etching treatment has the characteristics of low cost, non-contact and no subsurface damage, the prior patent describes a method for raising the damage threshold of the element by using plasma etching, but only aiming at polished glass, the prior working procedure still adopts a traditional physical mode, the existing subsurface damage is not completely removed, and the surface appearance deterioration caused by plasma etching leads to the element not having a smooth surface.
Based on the above discussion, how to avoid redeposited layer and subsurface defect damage caused by traditional processing methods and obtain fused quartz elements with smooth surfaces and high damage thresholds in the full process flow of fused quartz elements is of great importance for improving the performance of high-power laser devices.
Disclosure of Invention
The invention aims to provide a processing method of a fused quartz component with a smooth surface and a high damage threshold.
The whole process processing process is based on non-contact plasma etching and ion beam polishing post-treatment processes, so that redeposition layers and subsurface damages generated in the traditional processing mode are avoided, and a fused quartz element with a smooth surface and a high damage threshold is obtained. The method has the characteristics of simple operation, safety and reliability, and the fused quartz element with a smooth surface and a high damage threshold is obtained.
The technical scheme of the invention is as follows:
A method of processing a fused silica component having a smooth surface and a high damage threshold, the method comprising:
A) Cutting the blank, namely cutting the fused quartz blank into drawing sizes by using a wire cutting machine. Selecting a cutting line diameter of 0.125-0.25 mm and a cutting speed of 0.1-0.5 mm/min;
B) Milling and forming, namely milling and grinding the cut fused quartz to a specified external dimension by using a numerical control optical machining center according to milling and grinding tolerance required by a drawing. The milling and grinding process of the machined surface comprises rough milling and finish milling, and the milling and grinding process of the non-machined surface comprises rough milling, wherein the material removal depth of the rough milling process is d1. The material removal depth of the finish milling process is d2.
C) And (3) plasma deep etching, namely placing the fused quartz element which is subjected to precise milling and grinding forming on an objective table of a plasma processing machine tool, and fixing the fused quartz element by using a fixture clamp. And adjusting etching parameters of the plasma, and performing deep etching on the precisely ground element by using a plasma processing machine tool to completely remove the damaged layers on the surface and the subsurface of the fused quartz element, wherein the material removal depth of the plasma deep etching process is d3.
D) And (3) shallow plasma etching, namely placing the fused quartz element subjected to deep plasma etching on an objective table of a plasma processing machine tool, and fixing the fused quartz element by using a fixture. And adjusting etching parameters of the plasmas, carrying out shallow etching on the elements subjected to plasma deep etching by using a plasma processing machine tool, removing sediment on the surfaces and merging microstructures on the surfaces of the elements, wherein the material removal depth of a plasma shallow etching process is d4.
E) Ion beam polishing post-treatment, namely, for the fused quartz element after plasma shallow etching, further removing pollutants on the surface of the fused quartz by using ion beam polishing post-treatment, wherein the material removal depth of the ion beam polishing post-treatment process is d5, and finally, the smooth surface with the root mean square roughness being better than 1nm is obtained.
Between the steps (B), (C), (D) and (E), further comprising the step of ultrasonic and megasonic cleaning of the fused silica optical element.
The processing method of the fused quartz element with the smooth surface and the high damage threshold is characterized in that in ultrasonic and megasonic cleaning of the fused quartz element, the cleaning environment is hundred-grade clean. The cleaning medium is deionized water, and the deionized water resistance is more than or equal to 15MΩ. The ultrasonic frequency is 40-200 kHz, the cleaning time is 5-10 min, the cleaning temperature is 40-50 ℃, the megasonic frequency is 430 kHz-1 MHz, the cleaning time is 5-10 min, and the cleaning temperature is 40-50 ℃. And finally, dehydrating the element by using absolute ethyl alcohol.
The processing method of the fused quartz component with the smooth surface and the high damage threshold is characterized in that a rough milling process of milling and grinding is performed by using a diamond grinding wheel with abrasive grains fixed with 400-600 meshes, and a finish milling process of milling and grinding is performed by using a diamond grinding wheel with abrasive grains fixed with 800-1200 meshes.
The processing method of the fused quartz component with the smooth surface and the high damage threshold is characterized in that the material removal depths d1 and d2 are respectively 100-200 mu m and 20-50 mu m, the material removal depths d3 and d4 are respectively 10-50 mu m and 1-10 mu m, and the material removal depth d5 is 0.2-2 mu m.
The processing method of the fused quartz component with the smooth surface and the high damage threshold is characterized in that the working environment of plasma is atmospheric pressure, the radio frequency is 13.56MHz, the carrier gas is helium or argon, the reaction gas is carbon tetrafluoride or sulfur hexafluoride, the auxiliary gas is oxygen, the reaction power in the deep etching process of the plasma is 200-500W, the flow rate of the carrier gas is 1500-4000ml/min, the flow rate of the reaction gas is 120-200ml/min, the flow rate of the auxiliary gas is 20-50ml/min, the reaction power in the shallow etching process of the plasma is 100-200W, the flow rate of the carrier gas is 500-1500ml/min, the flow rate of the reaction gas is 50-100ml/min, and the flow rate of the auxiliary gas is 5-20ml/min.
The processing method of the fused quartz component with the smooth surface and the high damage threshold is characterized in that an excitation electrode of plasma in the plasma deep etching process is an aluminum electrode, and a layer of aluminum oxide ceramic film is plated on the surface of the electrode in a preferable mode. The excitation electrode of the plasma in the plasma shallow etching process is a graphite electrode. In the plasma shallow etching process, active particles in the plasma react with the graphite electrode, and the product is carbon dioxide, so that the adsorption accumulation of the reaction product on the surface of the processing element is further avoided.
The processing method of the fused quartz element with the smooth surface and the high damage threshold is characterized in that in the plasma deep etching and the plasma shallow etching processes, the plasma torch is positioned at the position 1-3mm above the fused quartz element, a grating type, spiral type or random path is adopted, the distance between adjacent etching points in the motion path and the distance between adjacent etching points in the motion path are in the range of 0.5-1mm, the equivalent residence time of single etching points of the fused quartz element in the plasma deep etching process is 2-10 s, namely the motion speed of plasma is 0.1-0.5 mm/s, and the equivalent residence time of single etching points of the fused quartz element in the plasma shallow etching process is 0.1-1 s, namely the motion speed of plasma is 1-10 mm/s.
A processing method of a fused quartz component with a smooth surface and a high damage threshold is characterized in that an ion beam polishing post-treatment process adopts an ion source of argon ions, the ion beam energy is 400-900 eV, the processing distance is 30-50 mm, and the ion beam incident angle is 40-70 degrees.
The invention has the following technical effects:
The whole process flow adopts a non-contact processing method, avoids normal positive pressure in the traditional processing mode, directly removes quartz with different depths after precise milling and grinding by plasma, completely removes surface and subsurface damaged layers, etches the plasma by using a graphite electrode, avoids deposition layers and pollutants of shallow plasma etching, and removes the deposition layers after plasma etching by adopting a post-treatment mode of ion beam polishing.
Drawings
FIG. 1 is a flow chart of a method of processing a high damage threshold fused silica component of the present invention;
Detailed Description
The invention is further illustrated below in connection with examples, which should not be taken as limiting the scope of the invention.
Referring to fig. 1, fig. 1 is a flow chart of a method of processing a high damage threshold fused silica component of the present invention. As can be seen from the figure, the embodiment of the invention takes a fused quartz element with phi 50 multiplied by 5mm as a processing object, and the processing method comprises the following steps:
a) Cutting the blank, namely cutting the fused quartz blank into drawing sizes by using a wire cutting machine. Selecting a cutting line diameter of 0.125mm and a cutting speed of 0.2mm/min;
B) Milling and forming, namely milling and grinding the cut fused quartz to a specified external dimension by using a numerical control milling and grinding machine. The milling and grinding process of the machined surface comprises coarse grinding and fine grinding, wherein a diamond grinding wheel with 600 meshes of fixed abrasive particles is adopted to remove materials with the depth of 120-150 mu m, and then a diamond grinding wheel with 1000 meshes of fixed abrasive particles is adopted to remove materials with the depth of 30-40 mu m.
C) And (3) performing plasma deep etching, namely performing deep etching on the precisely ground element by using a plasma processing machine tool, wherein the material removal depth of the plasma deep etching process is 25-30 mu m.
D) And (3) performing plasma shallow etching, namely performing shallow etching on the element subjected to plasma deep etching by using a plasma processing machine tool, wherein the material removal depth is 3-6 mu m.
E) And (3) performing ion beam polishing post-treatment, namely performing ion beam polishing post-treatment, wherein the material removal depth is 0.5-1 mu m, and finally obtaining the smooth surface with root mean square roughness better than 1 nm.
Between the step (B), the step (C), the step (D) and the step (E), the method further comprises the step of carrying out ultrasonic and megasonic cleaning on the fused quartz optical element by using deionized water with the water resistance of 15MΩ under hundred-grade clean environment. The ultrasonic frequency is 40, 75 and 120kHz, the cleaning time is 5-10 min, the cleaning temperature is 40-50 ℃, the megasonic frequency is 430 and 950MHz, the cleaning time is 5-10 min, and the cleaning temperature is 40-50 ℃. And finally, dehydrating the element by using absolute ethyl alcohol.
The excitation environment of the plasma is atmospheric pressure, the radio frequency is 13.56MHz, the carrier gas is helium, the reaction gas is carbon tetrafluoride, the auxiliary gas is oxygen, the plasma torch is positioned at 1-2 mm above the fused quartz element, a grating path is adopted, and the distance between adjacent etching points in the motion path are in the range of 0.5-1mm.
In the plasma deep etching process, the excitation electrode is an aluminum electrode plated with aluminum oxide ceramic, the reaction power is 300-400W, the flow rate of carrier gas is 2500-350 ml/min, the flow rate of reaction gas is 150-180 ml/min, and the flow rate of auxiliary gas is 20-30 ml/min. The equivalent residence time of a single etching point of the fused quartz component is 2-5 s, namely the movement speed of plasma is 0.2-0.5 mm/s.
In the plasma shallow etching process, the excitation electrode is a graphite electrode, the reaction power is 100-150W, the flow rate of carrier gas is 800-1200 ml/min, the flow rate of reaction gas is 50-80 ml/min, the flow rate of auxiliary gas is 5-15 ml/min, and the equivalent residence time of a single etching point of the fused quartz element is 0.1-0.5 s, namely the movement speed of plasma is 2-10 mm/s.
In the ion beam polishing post-treatment process, the ion source is argon ions, 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 degrees.
The fused quartz element is subjected to 1-on-1 laser damage threshold test according to international standard ISO 21254, the test laser wavelength is 355nm, the pulse width is 8ns, and test results show that the damage threshold of the fused quartz element with the damage probability of 0% before and after plasma processing in the processing method disclosed by the invention is increased from 7.8J/cm2 to 28.2J/cm2.
Experiments show that the whole process flow of the invention adopts non-contact processing, directly processes the precisely milled fused quartz, adopts a plasma etching method to remove the damaged layers on the surface and subsurface of the fused quartz, completely removes the damaged layers on the surface and subsurface of the fused quartz, adopts an ion beam post-processing mode to effectively remove pollutants on the surface of the fused quartz, ensures that the root mean square roughness of the final surface is better than 1nm, and obtains the fused quartz element with smooth surface and high damage threshold.
The method has the characteristics of simple operation, safety and reliability, adopts a non-contact processing method in the whole process, directly carries out combined processing on the precisely ground fused quartz blank, and obtains the fused quartz element with smooth surface and high damage threshold based on the post-treatment process of plasma etching with different depths and coupled ion beam polishing.