Additive repair method for fused quartz optical element surface microdefects

Abstract

The invention discloses an additive repairing method for micro defects on the surface of a fused quartz optical element, relates to the technical field of engineering optics, and aims to solve the problem that the surface appearance of Gaussian pits is easily generated on the repaired surface of the fused quartz optical element in an existing laser damage repairing mode. Comprising the following steps: step 1, screening and positioning the position of a surface defect of the fused quartz optical element, and pre-repairing the defect by using CO2 laser; the method comprises the following steps of 1, preparing a pre-repaired pit, 2, preparing a fused quartz nano-liquid composed of silicon dioxide nano-powder, a binder and a dispersant, and coating the bottom of the pre-repaired pit with the fused quartz nano-liquid, and 3, irradiating the coated defect with CO2 laser, melting the coated fused quartz nano-liquid, and carrying out micro-damage repair. According to the method, the laser damaged part of the fused quartz is subjected to additive repair by adopting a filling method, so that the planarization process of the pit type micro-defect is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of engineering optics, and in particular, to an additive repair method for surface micro-defects of fused silica optical elements. Background Art

[0002] Due to its excellent optical properties, mechanical strength, and chemical inertness, fused silica has been widely used in fields such as aerospace, astronomy, and military. When fused silica is used in extreme environments such as inertial confinement fusion (ICF), which usually requires extremely high laser power. Large-aperture fused silica optical elements (such as wedge lenses, grating debris shields, and vacuum windows) may be damaged by high-power lasers due to micro-defects. When the diameter of the damage point exceeds about 300 μm, it must be repaired to avoid further damage. If not repaired in time, the damage will spread and reduce the laser damage threshold of the optical element, becoming a bottleneck restricting the energy transmission of high-power laser systems. Existing laser damage repair methods can effectively inhibit the growth of damage on the surface of fused silica optical elements, but the repaired surface will produce a surface topography of Gaussian pits, enhancing the beam modulation effect of parallel light on downstream optical elements and increasing the damage probability of downstream optical elements. Therefore, developing an additive repair method for surface micro-defects of fused silica can achieve a good balance between performance recovery and cost control, which is of great significance for the long-term stable operation of key equipment such as high-power lasers. Summary of the Invention

[0003] The technical problem to be solved by the present invention is:

[0004] Existing laser damage repair methods easily cause a surface topography of Gaussian pits on the repaired surface of fused silica optical elements.

[0005] The technical solution adopted by the present invention to solve the above technical problem:

[0006] The present invention provides an additive repair method for surface micro-defects of fused silica optical elements, including the following steps:

[0007] Step 1: Screen and locate the position of the defect on the surface of the fused silica optical element, and use CO 2 laser to pre-repair the defect;

[0008] Step 2: Prepare the fused silica nano-liquid and coat the fused silica nano-liquid on the bottom of the pre-repaired pit. The specific steps are as follows:

[0009] ① Weigh and pre-treat the silicon dioxide powder: Weigh the silicon dioxide nano-powder and perform drying treatment;

[0010] ② Prepare the binder solution: Heat deionized water until it boils, add the binder in batches to the boiling water, stir while adding, let it cool to room temperature and then stand still to obtain the binder solution;

[0011] ③ Prepare the liquid-phase mixture: Add a dispersant to the binder solution obtained in step ② and stir evenly to obtain a mixed solution;

[0012] ④ Add solid-phase particles: Stir the mixed solution obtained in step ③ at high speed, add the dried silica nano-powder in batches, and stir until it becomes clear to obtain the fused silica nano-liquid;

[0013] ⑤ Coat the defect: Use a syringe to precisely coat the fused silica nano-liquid to the bottom of the pit pre-repaired in step one;

[0014] Step three, use CO 2 Laser irradiate the coated defect to melt the coated fused silica nano-liquid for micro-damage repair.

[0015] Further, the fused silica nano-liquid includes by mass parts: (26 - 27) parts of deionized water, 20 parts of silica nano-powder, (53 - 54) parts of binder, and (0.2 - 0.3) parts of dispersant.

[0016] Further, the binder is selected from hydroxypropyl methylcellulose, and the dispersant is selected from anionic polycarboxylate ammonium salt.

[0017] Further, in step two ⑤, the needle diameter of the syringe is 125 μm. Use a CCD camera to locate the damage point, control the syringe through a three-axis moving stage, and fill the fused silica nano-liquid to the damage point.

[0018] Further, CO 2 The wavelength of the laser is 10.6 μm.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] The additive repair method for surface micro-defects of fused silica optical elements in the present invention uses the filling method to additively repair the damaged parts of fused silica by laser, realizing the flattening process of pit-type micro-defects. The fused silica nano-liquid in the present invention has uniform distribution, continuous stability, suitable viscosity, and good rheological properties to achieve appropriate fluid flow filling behavior.

[0021] The method of the present invention can flexibly adapt to different repair requirements, improving the adaptability and stability of the process; the present invention optimizes the composition of the best fused silica nano-liquid for filling surface micro-defect sites of fused silica to achieve high-quality additive repair.

[0022] The present invention can achieve high-precision repair of complex and deep defects, not only improving the repair efficiency and quality of surface micro-defects of fused silica optical elements, reducing the replacement cost of expensive optical elements, but also promoting the application of additive manufacturing technology in the optical field, and providing new ideas and technical support for the development and optimization of related processes.

[0023] The present invention has the advantages of fast repair speed, simple operation and low cost. Description of the Drawings

[0024] Figure 1 It is a flowchart of the additive repair method for surface micro-defects of fused silica optical elements in the embodiment of the present invention;

[0025] Figure 2 It is a schematic diagram of the functions of the binder and the dispersant in the fused silica nano-liquid in the embodiment of the present invention. Among them, a is the function of the binder in the fused silica nano-liquid, and b is the function of the binder in the fused silica nano-liquid;

[0026] Figure 3 It is a physical diagram of the fused silica nano-powder solution in the embodiment of the present invention;

[0027] Figure 4 It is the CO in the embodiment of the present invention 2 Laser device schematic diagram;

[0028] Figure 5 It is a graph of the viscosity change of solutions with different solid-phase contents in the embodiment of the present invention;

[0029] Figure 6 It is a graph of the void size and number of the solidified surface of solutions with different solid-phase contents in the embodiment of the present invention;

[0030] Figure 7 It is the melting process of the fused silica nano-liquid in the surface micro-defects of fused silica in the embodiment of the present invention;

[0031] Figure 8 It is the microscopic image, morphological characteristics and cross-sectional shape of the micro-defect repair points a-d in the embodiment of the present invention;

[0032] Figure 9 It is the beam modulation effect diagram of the micro-defect morphology in the embodiment of the present invention. Among them, (a) in the figure is the damaged point and (b) is the repaired point;

[0033] Figure 10 It is the axial light intensity curve graph of different transmission distances in the embodiment of the present invention. Among them, (a) in the figure is the damaged point and (b) is the repaired point;

[0034] Figure 11It is the modulation diagram of beam transmission in the embodiments of the present invention, where Figures (a)-(d) are damage points; Figures (a+)-(d+) are repair points;

[0035] Figure 12 It is the light field intensity diagram at the maximum wave peak in the embodiments of the present invention, where Figures (a)-(d) are damage points and Figures (a+)-(d+) are repair points;

[0036] Figure 13 It is the Raman spectrum of the repair points after additive repair of the surface microdefects of fused silica and the fused silica substrate in the embodiments of the present invention. Specific embodiments

[0037] In order to enable those skilled in the art to better understand the solution of the present invention, the exemplary embodiments or examples of the present invention will be described below in conjunction with the accompanying drawings. Obviously, the described embodiments or examples are only part of the embodiments or examples of the present invention, rather than all of them. All other embodiments or examples obtained by those of ordinary skill in the art based on the embodiments or examples of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0038] To make the above objects, features, and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0039] In a typical embodiment, as Figure 1 shown, the present invention provides a method for additive repair of surface microdefects of a fused silica optical element, including the following steps:

[0040] Step 1. Screen and locate the position of the surface defects of the fused silica optical element, and pre-repair the defects using CO 2 laser;

[0041] Step 2. Prepare a fused silica nano-liquid and coat the solution on the bottom of the pre-repaired pit. The specific steps are as follows:

[0042] ① Pretreatment of silica powder: Weigh a sufficient amount of silica nano-powder and dry it;

[0043] ② Preparation of binder solution: Heat deionized water to boiling, add the binder in batches to the boiling water, stir while adding, and let it stand after cooling to room temperature to obtain the binder solution;

[0044] ③ Preparation of liquid-phase mixture: Add a dispersant to the binder solution obtained in ② and stir evenly to obtain a mixed solution;

[0045] ④Solid-phase particle addition: The mixed solution obtained by high-speed stirring in ③ is added with dried silica nanopowder in batches and stirred until it becomes clear to obtain a fused silica nano-liquid;

[0046] ⑤Solution coating defect: The fused silica nano-liquid is precisely coated onto the bottom of the pit pre-repaired in Step 1 using a syringe;

[0047] Step 3. Use CO 2 Laser irradiates the coated defect to melt the coated fused silica nano-liquid for micro-damage repair.

[0048] In a typical embodiment, preferably, the fused silica nano-liquid includes, by mass parts: (26 - 27) parts of deionized water, 20 parts of silica nanopowder, (53 - 54) parts of binder, and (0.2 - 0.3) parts of dispersant. To ensure the uniform distribution, continuous stability, appropriate viscosity, and good rheological properties of the fused silica nano-liquid. The added binder and dispersant evaporate into the air together with deionized water during the heating process of the repair to avoid affecting the melting and condensation of the silica nanopowder and ensure that the silica forms transparent fused silica glass.

[0049] In a typical embodiment, preferably, the binder is selected from hydroxypropyl methylcellulose, and the dispersant is selected from anionic polycarboxylate ammonium salt.

[0050] As Figure 2 shown, the density of the silica powder is significantly higher than that of deionized water, resulting in easy stratification and precipitation of the mixed solution. To improve this phenomenon, hydroxypropyl methylcellulose (HPMC) is added as a binder to form clusters by increasing the solution viscosity so that the suspended particles coagulate with each other. Due to the intermolecular force, the silica powder particles cannot be evenly distributed in the solution. Adding an anionic polycarboxylate ammonium salt dispersant can form an attachment layer on the surface of the solid-phase particles, increase the charge amount on the particle surface, thereby increasing the repulsive force between particles, reducing cluster formation, stabilizing the suspension of the solution, and improving the leveling property of the fused silica nano-liquid.

[0051] Determination of the selection of the silica content in the fused silica nano-liquid:

[0052] The flow behavior of a viscous fluid is expressed by the classical Ostwald - de Waele relationship:

[0053]

[0054] In the formula, η —— effective viscosity (Pa·s);

[0055] τ —— shear stress (MPa);

[0056] n —— fluid characteristic index;

[0057] k——Viscosity coefficient;

[0058] ——Shear rate (s -1 ).

[0059] The fused silica nanofluid needs to have good fluidity in an extremely fine needle tube and should exhibit shear-thinning consistency behavior. When the liquid flows out of the output needle, as the diameter of the tube gradually decreases, the shear rate gradually increases, and the viscosity of the solution should gradually decrease. That is, the fused silica nanofluid should be a pseudoplastic fluid (0 < n < 1).

[0060] Viscosity measurements were carried out on fused silica nanofluids with different solid-phase contents (10 wt.%, 15 wt.%, 20 wt.%). The measured data were non-linearly curve-fitted using Equation (1), as Figure 5 shown, to obtain the fluid characteristic index n and viscosity coefficient k of the fused silica nanofluid. The fitting equations for the three different solid-phase content fused silica nanofluids are respectively: The viscosity fitting equation shows that the fluid characteristic coefficient n of the prepared fused silica nanofluid is less than 1, indicating its pseudoplastic fluid characteristics. As the solid-phase content increases, the surface area of the silica cluster particles in the liquid increases, and the adhesion between the binder and the particles becomes more prominent, resulting in a significant increase in the effective viscosity of the liquid, which is beneficial to the bonding between the solution and the substrate. Especially during the fused silica repair process, it improves the coating uniformity and stability.

[0061] After the fused silica nanofluid is coated on the surface of the component, the moisture in the solution will gradually evaporate into the atmosphere over time, and gradually form the surface morphology of the fused silica cluster particles. The final formed surface morphology after solidification is the main factor for judging the quality of the coating effect. There will inevitably be bubbles in the fused silica nanofluid. During the solidification process of the solution, void structures gradually form at the positions of the bubbles. There are irregular void structures on the surface of the solidified fused silica cluster particles. There is a certain probability that bubbles will be generated under the action of laser at the void structures on the surface of the particle clusters, accumulating inside the fused silica repair area. The presence of bubbles will have a great adverse impact on the surface micro-defect repair results. Try to reduce the void characteristic morphology on the surface of the fused silica cluster particles after solidification. As Figure 6 shown, by observing the surfaces of different solid-phase content solutions after solidification, as the solid-phase content gradually increases, the average number of void structures gradually decreases, and the volume of fusible fused silica cluster particles per unit area increases accordingly. The thickness of the repair layer after melting in the surface micro-defects will increase accordingly, which has a promoting effect on the surface flattening trend after repair. However, when the solid-phase content exceeds 21 wt.%, the liquid does not have obvious flow characteristics and presents a solid state. Therefore, 20 wt.% is preferably the maximum solid-phase content.

[0062] In a typical embodiment, preferably, the needle diameter of the syringe in step 2⑤ is 125 μm, a CCD camera is used to locate the damage point, and the syringe needle is controlled by a three-axis moving stage to fill the fused quartz nanofluid into the damage point.

[0063] In a typical embodiment, preferably, the Figure 4 The CO shown 2 Laser device, CO 2 The laser device uses a Gaussian beam with a wavelength of 10.6 μm and adjusts the radio frequency power to excite CO 2 Laser output, generating linearly polarized rectangular CO 2 Laser pulse; The modulator works synchronously with the laser to modulate the laser pulse into a rectangular linear polarized laser pulse. The frequency, pulse width and power of the laser pulse can be adjusted by the modulator; After passing through the beam splitter and beam expander, the diffracted laser pulse enters the galvanometer scanning system, which includes a focusing lens to ensure that the laser pulse is 1 / e on the surface of the fused silica substrate. 2 A light spot is formed at the output end of the laser beam; a suction nozzle device is provided to remove the vaporized material during the processing to prevent it from redepositing and contaminating the processed surface.

[0064] The specific laser defocus distance, laser power and laser irradiation time are adjusted according to the specific size of the defect. In order to minimize the extension of the pit edge caused by molten flow during the repair process, the spot size used in additive repair is smaller than the spot size used when presetting pit-type micro-defects. Then the laser power is further reduced to ensure that under continuous laser irradiation, the solution coated on the substrate and the micro-defect surface are in the molten flow stage, and evaporation of the substrate material in the laser irradiation area does not occur, so as to avoid "secondary damage" to micro-defects caused by secondary laser processing.

[0065] By changing the defocus distance of the beam end, CO 2 The spot diameter of the laser device, the laser defocus distance d f The spot diameter r f for:

[0066]

[0067] where d f is the defocus distance; r 0 is the focus spot radius; L r is the Rayleigh length.

[0068] like Figure 7 As shown in the figure, the surface of the clusters formed by the fused quartz nanofluid after solidification is in a semi-solid and semi-liquid state. 2Under the action of laser energy, it gradually changes from a semi-solid and semi-liquid state to a typical fused silica material. The surface morphology after additive repair is still affected by Cv 2 the influence of the laser energy distribution, and the spatial distribution of micro-defects shows a Gaussian distribution. The specific changes in the pre-placed solution on the surface of micro-defects melting over time are as follows:

[0069] At t = 0.1 s, the convex area at the center of the solidified cluster particles enters the melting stage. By t = 0.5 s, the water in the coating solution quickly evaporates and shrinks, entering the initial phase change molten pool stage, and the laser mainly eliminates the surface morphology with a large curvature to achieve flattening; by t = 1 s, the cluster particles have melted and shrunk, entering the molten pool expansion stage; by t = 1.5 s, the laser action area approaches the spot size, and the melt flows and redistributes in the XY plane to form a smooth repair surface.

[0070] The beneficial effects of the present invention will be described below in conjunction with specific embodiments.

[0071] Example 1

[0072] Step 1: Screen and locate the positions of surface defects a, b, c, and d on the surface of four fused silica optical elements with different sizes of surface defects, and use a CO laser with a wavelength of 10.6 μm 2 to pre-repair each defect;

[0073] Step 2: Prepare the fused silica nano-liquid and coat the fused silica nano-liquid on the bottom of the pre-repaired pit. The specific steps are as follows:

[0074] ① Weigh and pre-treat the silica powder: Weigh a sufficient amount of silica nano-powder (average particle size is 30 nm, specific surface area is 350 m 2 / g), and perform drying treatment on it;

[0075] ② Prepare the binder solution: Heat 26.59 g of deionized water to boiling, and add 53.15 g of hydroxypropyl methylcellulose to the boiling water in batches, stirring while adding, and let it stand after cooling to room temperature to obtain the binder solution;

[0076] ③ Prepare the liquid-phase mixture: Add 0.26 g of anionic polycarboxylate ammonium salt to the binder solution obtained in step ② and stir evenly to obtain a mixed solution;

[0077] ④ Add solid-phase particles: Stir the mixed solution obtained in step ③ at a high speed of 800 r / min, and add 20 g of dried silica nano-powder in batches, and stir until it becomes clear to obtain the fused silica nano-liquid as Figure 3 shown;

[0078] ⑤ Coating defect: Use a syringe with a needle diameter of 125 μm to suck equal amounts of fused silica nano-liquid respectively, and precisely coat it to the bottom of the pit pre-repaired in Step 1 through a three-axis moving stage. Use a scraper to remove the excess solution around the damaged point;

[0079] Step 3: Locate the surface defects of a, b, c, and d. Move the center of the laser spot to the central area of the micro-defect after coating, and use lasers with different powers and spot sizes for melting repair respectively. Melt the coated fused silica for micro-damage repair. The laser process parameters are shown in Table 1 below.

[0080] To minimize the extension caused by the molten flow at the edge of the pit, the spot size used for additive repair is smaller than the spot size used for preset pit-shaped micro-defects. Then, further reduce the laser power to ensure that both the substrate and the solution coated on the surface of the micro-defect are in the molten flow stage under continuous laser irradiation, without the evaporation and vaporization of the substrate material in the laser irradiation area, and try to avoid the "secondary damage" of the micro-defect caused by secondary laser processing. Use a white light interferometer to measure the surface topography of the pit after melting repair. The microscopic images, topography features, and cross-sectional shapes of different repaired pits are as Figure 8 shown.

[0081] Table 1

[0082]

[0083]

[0084] For the damaged point a, compare the influence of the change in the surface topography before and after repair on the modulation degree of the incident light beam. The radius of the repaired damaged point is concentrated around 350 μm. Set the size of the receiving and observing screen for beam modulation to 4×4 mm. Assume that the maximum distance of beam transmission is 1000 mm, and calculate the light intensity distribution and modulation degree value every 1 mm. The light intensity distribution of a plane light with unit amplitude passing through the micro-defect topography along the incident direction is as Figure 9 shown. There is an obvious beam modulation diffraction phenomenon when the plane beam passes through the micro-defect surface, and the amplitude and phase of the incident light are modulated.

[0085] Extract the diffraction patterns of the receiving screen at the transmission distances Z = 100, 500, and 1000 mm, and the on-axis light intensity distributions are as Figure 10As shown, the light field distributions at different distances show that Poisson bright spots appear on the beam transmission axis. As the transmission distance increases, the off-axis annular fluctuations gradually expand outwards, and the light intensity action range of the Poisson bright spots gradually shows a divergent state. For the light intensity distributions at different transmission distances, the on-axis Poisson bright spots are always lower than the light field intensity at the off-axis annular fluctuation positions. From the light intensity curves and light field distributions at different distances, it can be seen that the additive repair has an obvious effect on slowing down the depth of the repair point, but the slowdown of the depth characteristic value has no obvious improvement on the modulation effect of the long-distance beam. It is speculated that the reason is that the degree of depth slowdown is small or the beam transmission distance is large, diluting the influence of the slowdown depth on the three-dimensional morphology change of the repair point.

[0086] Quantitative analysis was carried out on the beam modulation degree within the range of 0 - 100 mm. The light intensity modulation degree M of the near-field beam of different additive repair points is as Figure 11 shown. The maximum value of the modulation degree appears at the position close to the additive repair point, which is called the first maximum peak of annular modulation. Different degrees of enhanced annular regions appear in the near-field light intensity distributions of different additive repair sites. The variation distributions of the light field intensity at the first peak of beam modulation of micro-defect repair sites with different sizes are as Figure 12 shown, indicating that the slowdown of the depth characteristic value of micro-defects has an obvious improvement effect on the first maximum peak of the annular modulation of the beam. The slowdown ratios of the maximum peaks of the modulation degrees of repair sites (a), (b), (c), and (d) are 23.82%, 28.93%, 44.35%, and 27.24% respectively. The degree of reduction of the light intensity modulation degree is consistent with the degree of slowdown of the micro-defect depth repair. By using additive repair to slow down the curvature morphology of micro-defects, the light intensity modulation degree of the defect site on the incident beam can be effectively controlled, thereby reducing or even eliminating the possibility of cascade damage to downstream optical elements caused by beam modulation at the defect site.

[0087] As Figure 13 shown in the Raman spectroscopy analysis, the spectral characteristics of the fused silica materials formed after laser melting treatment at repair sites (a) and (b) show a high degree of similarity with those of the substrate. Both show five significant Raman active peaks: D 1 , D 2 , SS, TO, and LO; compared with the standard spectrum, it can be seen that the material structures in different additive repair regions are only slightly affected by the laser energy accumulation of CO 2 laser. The intensities of the D 1 and D 2 defect bands in the Raman spectrum represent the four-membered ring and three-membered ring structures of fused silica respectively. Due to the action of the laser thermal effect, the intensities of the D 1 and D 2 defect bands in the repair region are slightly higher than those of the fused silica substrate.

[0088] The average elastic modulus of additively repaired fused silica is 70.3 GPa, and the average hardness is 9.41 GPa; the average elastic modulus of the fused silica substrate (KN7980) is 69.6 GPa, and the average hardness is 9.42 GPa. The elastic properties of additively repaired fused silica are slightly better than those of the substrate, and there is no obvious difference in hardness from the substrate.

[0089] Theoretically, a large amount of fused silica nanofluid can slow down the surface morphology to a large extent, but an excessive amount of solution may lead to irregular coating morphology. Therefore, regardless of the defect size, an excessive amount of solution should not be used; for large-sized pits, laser melting repair should be carried out in small amounts and multiple times; for small-sized pits, single repair can significantly repair more than half of the volume.

[0090] 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 invention, and these changes and modifications will all fall within the scope of protection of the present invention.

Claims

1. An additive repair method for micro-defects on the surface of a fused quartz optical element, characterized in that: The steps include: Step 1: Screen and locate the location of surface defects of fused quartz optical components, and use CO2 laser to pre-repair the defects; Step 2: Prepare fused quartz nanofluid and apply the fused quartz nanofluid to the bottom of the pre-repaired pit. The specific steps are as follows: ① Weighing silica powder and pre-treating: Weighing silica nanopowder and drying it; ②Prepare the binder solution: heat the deionized water until it boils, add the binder into the boiling water in batches, stir while adding, cool to room temperature and let stand to obtain the binder solution; ③Preparing a liquid mixture: adding a dispersant to the binder solution obtained in step ② and stirring evenly to obtain a mixed solution; ④ Add solid phase particles: stir the mixed solution obtained in step ③ at high speed, add dried silicon dioxide nanopowder in batches, stir until it is clear, and obtain fused quartz nanofluid; ⑤ Coating defects: Use a syringe to accurately coat the fused quartz nanofluid to the bottom of the pit pre-repaired in step 1; Step 3: Use CO2 laser to irradiate the defects after coating, melt the coated fused quartz nanofluid, and perform micro-damage repair.

2. The additive repair method for surface micro-defects of fused silica optical elements according to claim 1, characterized in that: The fused quartz nano-liquid comprises, by weight: deionized water (26-27) parts, silicon dioxide nano-powder 20 parts, a binder (53-54) parts and a dispersant (0.2-0.3) parts.

3. The additive repair method for surface micro-defects of fused silica optical elements according to claim 2, characterized in that: The binder is selected from hydroxypropyl methylcellulose, and the dispersant is selected from anionic polycarboxylate ammonium salts.

4. The additive repair method for surface micro-defects of fused silica optical elements according to claim 3, characterized in that: The needle diameter of the syringe in step 2⑤ is 125 μm. A CCD camera is used to locate the damage point, and the syringe is controlled by a three-axis moving stage to fill the fused quartz nanofluid into the damage point.

5. The additive repair method for surface micro-defects of fused silica optical elements according to claim 4, characterized in that: The wavelength of CO2 laser is 10.6μm.

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