A post-treatment method for fused silica components with high laser damage threshold

Abstract

The present invention discloses a post-treatment method for fused silica components with a high laser damage threshold. The specific operation process is as follows: First, the surface of the fused silica component is etched by an ion beam with a large incident angle to remove metal impurity defects and broken-type defects on the surface of the component; after ion beam etching, oxygen ions are implanted into the fused silica component to introduce oxygen ions and composite the oxygen-deficient structural defects on the surface of the component; then, the ion-implanted fused silica component is subjected to subsequent annealing treatment to further eliminate the oxygen-deficient structural defects on the surface of the component and even in the material itself; finally, the fused silica component is ultrasonically cleaned with deionized water and absolute ethanol. The method of the present invention can make up for the limitations of a single method, and at the same time can systematically and effectively eliminate the precursors that induce laser damage of fused silica: metal impurity defects, broken-type defects, and oxygen-deficient structural defects, and significantly improve the laser damage resistance performance of the fused silica component.

Description

Technical Field:

[0001] The present invention relates to the technical field of optical element manufacturing, and particularly relates to a post-treatment method for fused silica elements with a high laser damage threshold. Background Art:

[0002] Fused silica materials have good optical, thermal and mechanical properties and are mainly used to manufacture ultraviolet optical elements such as shielding sheets, focusing lenses, mirrors, polarizers, sampling gratings, etc., and are widely used in high-power solid laser devices. However, during the initial optical polishing process of fused silica elements, metal impurity defects (such as Ce, Fe, Al, etc.), broken-type defects (such as scratches, pits, etc.) and oxygen-deficient structural defects (such as E' color centers, oxygen vacancies, etc.) will be introduced. Metal impurities mainly come from polishing powders, polishing tools and optical cleaning, are randomly distributed in the polishing deposition layer on the surface of fused silica, and even embedded in defects such as subsurface scratches and pits. Broken-type defects mainly come from the plastic deformation and brittle fracture of materials caused by the normal load during the optical polishing process and are distributed in the subsurface layer of fused silica. In addition, during the optical polishing process, the composition and structure of the surface and deeper subsurface layers also change, which will lead to the formation of oxygen-deficient structural defects. Metal impurity defects and oxygen-deficient structural defects will absorb ultraviolet lasers, resulting in local temperature rise and very large stresses, and even causing permanent damage. At the same time, these defects will change the initial bandgap structure of fused quartz and trigger new photon excitations under intense laser irradiation, seriously affecting the laser-induced non-linear excitation (multi-photon ionization and avalanche ionization) of fused silica, making the optical material more prone to damage. Broken-type defects will enhance scattering, resulting in laser energy loss, causing enhanced light field modulation at the defects and downstream optical elements, and reducing the mechanical strength of the optical elements, thereby reducing the laser damage performance of fused silica elements. Under ultraviolet laser irradiation, these three types of defects are considered to be the precursors inducing laser damage of fused silica elements, seriously reducing the laser damage threshold and service life of the elements. In addition, in the actual operating environment, the damage threshold of the elements is much lower than the intrinsic damage threshold of the fused silica material, which is also closely related to the oxygen-deficient structural defects introduced in the material during the growth process. Therefore, there is an urgent need to find a suitable method to systematically and effectively eliminate these three types of defects in order to improve the laser damage resistance performance of the elements and extend their service life, which has important economic value and engineering significance for the high-throughput output and stable operation of laser devices.

[0003] Ion beam etching is achieved by bombarding the material surface with energetic ions to generate cascade collisions, thereby sputtering surface atoms to achieve the purpose of etching and removing the material surface. As an anisotropic dry etching technique, the replication and expansion of surface and subsurface fragmentation defects are avoided during the etching process, and these defects can be completely removed. The ion beam etching technique is a non-contact atomic-level removal method that can obtain a super-smooth surface, does not introduce new contamination, causes little damage to the substrate material, and has low stress. In addition, ion beam etching has good stability and uniformity, and the process parameters and depth are precisely controllable. Therefore, ion beam etching can be used to physically polish the surface of fused silica to remove surface metal impurity defects and fragmentation defects.

[0004] Ion implantation is an effective material surface modification technique that can be used to regulate the surface composition and structure of materials, thereby improving the surface properties of materials. In addition, ion implantation is a non-equilibrium process that is not restricted by solid solubility and thermal equilibrium. The implantation concentration and depth can be precisely controlled through ion implantation parameters, and the process has good repeatability, stability, and strong controllability. Therefore, the method of oxygen ion implantation can be used to repair the oxygen-deficient structure defects on the surface of fused silica. After oxygen ion implantation on the surface of fused silica, thermal annealing treatment is carried out. On the one hand, diffusion can expand the distribution depth range of oxygen ions and improve the uniformity of oxygen ion distribution; on the other hand, it is beneficial to the migration of defects to make the defects recombine, further eliminating the oxygen-deficient structure defects on the surface and even in the material itself.

[0005] Under ultraviolet laser irradiation, metal impurity defects, fragmentation defects, and oxygen-deficient structure defects are the main precursors that are prone to inducing laser damage in fused silica components. At present, existing technologies cannot completely eliminate these three types of defects. Therefore, the present invention uses ion beam etching combined with oxygen ion implantation and post-annealing treatment to systematically and effectively eliminate the damage precursors of fused silica components, so as to improve the laser damage resistance performance and service life of the components. Summary of the Invention:

[0006] In order to eliminate the precursors of laser damage in fused silica components: metal impurity defects, fragmentation defects, and oxygen-deficient structure defects, the present invention provides a post-treatment method for fused silica components with a high laser damage threshold. This method can systematically and effectively remove the precursors of laser damage in fused silica components to achieve the purpose of significantly improving the laser damage resistance performance of fused silica components.

[0007] To achieve the above object, the technical solution adopted by the present invention is: to provide a post-treatment method for fused silica components with a high laser damage threshold, including the following steps:

[0008] (1) Ion beam etching: Etch the surface of the fused silica component with a large-angle ion beam, which can effectively remove metal impurity defects and fragmentation defects on the surface of the component;

[0009] (a) The gas ion source used is high-purity argon; the ion beam energy is 100 eV to 1500 eV; the beam current density is 0.28 mA / cm 2 ~1.91 mA / cm 2 ; the angle between the ion beam and the normal of the fused silica substrate is 60° to 90°; a neutralizer is used to provide negatively charged electrons to neutralize the positively charged ion beam, and the emitted electron current is 100 mA to 900 mA;

[0010] (b) Part of the fused silica element is shielded. Within a fixed time, based on the ion beam etching parameters in (a), the fused silica element is etched to create a step, and then a profilometer is used to measure the step height, i.e., the etching depth, at the boundary between the unetched area and the etched area. The etching rate of the fused silica element for different ion beam parameters can be calculated based on the etching depth and the etching time used. To ensure the accuracy and reliability of the etching rate, the etching depth needs to be greater than 10 μm;

[0011] (c) Based on the etching rate calibrated in step (b), the etching depth of the fused silica element can be accurately controlled. The final etching depth of the fused silica element depends on the distribution depth of the broken-type defects. To completely remove the broken-type defects, the fused silica element is etched iteratively with an ion beam, that is, after etching a certain depth, an optical microscope is used to observe the surface broken-type defects until the broken-type defects are completely removed, and then the etching is stopped;

[0012] (d) To ensure uniform and effective removal of the broken-type defects, during the etching process, the fused silica element needs to be etched by rotation; to avoid the generation of stress, the fused silica element needs to be etched intermittently, that is, after etching a depth of 500 nm, the etching is stopped for 10 min;

[0013] (2) Ion implantation: Oxygen ions are implanted on the surface of the fused silica element after ion beam etching in step (1) to introduce oxygen ions and repair the oxygen-deficient structure defects;

[0014] (a) The gas ion source used is high-purity oxygen; the ion implantation energy is 10 keV to 50 keV; the ion fluence is 1×10 16 ions / cm 2 ~3×10 17 ions / cm 2 ; including single and multiple implantations at different ion energies and ion fluences;

[0015] (b) During the implantation process, to avoid the generation of stress, the sample stage needs to be cooled by circulating water;

[0016] (3) Post-annealing treatment: For the fused silica component after ion implantation in step (2), a clean high-temperature tube-type atmosphere furnace is used to perform subsequent annealing treatment on the fused silica component to further eliminate the oxygen-deficient defects on the surface and even in the material itself. The atmosphere used is high-purity oxygen, the oxygen flow rate is 100 sccm to 500 sccm, the annealing temperature is 300 °C to 900 °C, the annealing time is 0.5 h to 8 h. To avoid the generation of stress, the heating rate is controlled at 5 °C / min to 15 °C / min, the cooling rate is controlled at 5 °C / min to 10 °C / min, and it is cooled to room temperature;

[0017] (4) Cleaning of fused silica component: The fused silica component after annealing in step (3) is ultrasonically cleaned with deionized water and anhydrous ethanol respectively, and the cleaning time is 30 min for both, and then it is naturally dried in a clean environment.

[0018] The beneficial effects of the present invention are as follows: Ion beam etching has the characteristic of anisotropy. By using large incident angle ion beam etching on the fused silica component, the metal impurity defects and broken-type defects on the surface of the component can be completely removed; as a non-contact atomic-level removal method, it can obtain a super-smooth surface, and will not introduce new pollution, with little damage and stress to the substrate material; in addition, ion beam etching has good stability and uniformity, and the process parameters and depth are precisely controllable.

[0019] Oxygen is an element of the fused silica matrix. Oxygen self-ion implantation will not introduce impurity ions. By using the method of ion implantation to provide oxygen ions on the surface of fused silica, the oxygen-deficient structural defects on the surface of the component can be recombined; after oxygen ions are implanted on the surface of fused silica, thermal annealing treatment is carried out. Through diffusion, the distribution depth range of oxygen ions can be expanded and the uniformity of oxygen ion distribution can be improved, and it is beneficial to the migration of defects to make the defects recombine, further eliminating the oxygen-deficient structural defects on the surface and even in the material itself.

[0020] The present invention provides a post-treatment method for high-laser-damage fused silica components, namely ion beam etching combined with oxygen ion implantation and post-annealing treatment, which makes up for the limitations of a single method, and can systematically and effectively eliminate the precursors that induce laser damage in fused silica: metal impurity defects, broken-type defects and oxygen-deficient structural defects, thereby significantly improving the laser damage threshold and service life of the components, and having important economic value and engineering significance for the high-throughput output and stable operation of laser devices. Brief description of the drawings:

[0021] Figure 1 is a process schematic diagram of the present invention;

[0022] Figure 2(a) and (b) are microscope images of the fused silica surface during the ion beam etching process in the first embodiment of the present invention; (c) and (d) are the impurity element distributions on the fused silica surface before and after ion beam etching; (e) is the EPR spectrum of the fused silica before and after ion implantation and annealing; (f) is the laser damage threshold of the fused silica component under different processing procedures;

[0023] Figure 3 (a) and (b) are microscope images of the fused silica surface during the ion beam etching process in the second embodiment of the present invention; (c) and (d) are the impurity element distributions on the fused silica surface before and after ion beam etching; (e) is the EPR spectrum of the fused silica before and after ion implantation and annealing; (f) is the laser damage threshold of the fused silica component under different processing procedures. Specific embodiments:

[0024] The following makes a detailed description of the specific embodiments of the present invention.

[0025] First embodiment

[0026] The size of the fused silica optical element is 30mm×30mm×4mm. A silicon wafer is used to shield a part of the fused silica element area. An argon ion beam with an energy of 800eV, a beam current density of 0.83mA / cm 2 、an incident angle of 70° is used to etch the surface of the element for 450min. The emitted electron current is 360mA. The step height, that is, the etching depth of 11.62μm, is measured by a profilometer at the boundary between the unetched area and the etched area. Then the etching rate of the ion beam on the fused silica element is 25.82nm / min; the size of the fused silica element to be processed is 50mm×50mm×5mm. The surface of the fused silica element is rotationally etched using the same ion beam parameters as those for etching rate calibration. Every time it is etched by 500nm, the etching is stopped for 10min, and an optical microscope is used to observe the surface fragmentation-type defects until the fragmentation-type defects are completely removed. The final etching depth is 2μm; after ion beam etching, an oxygen ion implantation is performed on the surface of the element using a high cleanliness ion implantation machine. The ion energy is 50keV, and the fluence is 1×10 17 ions / cm 2 ; after ion implantation, the fused silica element is subjected to an oxygen atmosphere post-annealing treatment using a clean high-temperature tube furnace. The gas flow rate is 300sccm. It is heated to 700°C at a heating rate of 10°C / min, held for 2h, and then cooled to room temperature at a cooling rate of 5°C / min; finally, the annealed fused silica element is ultrasonically cleaned with deionized water and absolute ethanol respectively, and the cleaning time is 30min for both, and then it is naturally dried in a clean environment.

[0027] An optical microscope is used to in-situ observe the fragmentation-type defects during the ion beam etching process, as Figure 2As shown in (a) and (b), after ion beam etching, the polished deposition layer was removed, exposing the fragmented defects. After ion beam etching for 2 μm, the fragmented defects were completely removed. The metal impurity distribution on the surface of the component before and after ion beam etching was measured by time-of-flight secondary ion mass spectrometry, as Figure 2 shown in (c) and (d), there were a large number of metal impurities on the surface before ion beam etching. After ion beam etching, the metal impurity content decreased sharply and remained unchanged with the increase of the test time, which were the metal impurities inherent in the bulk material, indicating that ion beam etching could remove the metal impurity defects on the surface of the component. The EPR spectra of fused silica before and after ion implantation and annealing treatment were measured by electron paramagnetic resonance spectrometer, as Figure 2 shown in (e), all samples showed an EPR signal with a g factor of 2.006, corresponding to oxygen vacancy defects. After ion implantation and post-annealing treatment, the concentration of oxygen vacancies decreased in turn, indicating that oxygen ion implantation could recombine the oxygen-deficient structure defects, and post-annealing treatment could further eliminate the oxygen-deficient structure defects on the surface and even in the material itself. The R:1 laser damage threshold of fused silica components under different treatment procedures was measured by a Nd:YAG laser with a 355 nm laser wavelength, as Figure 2 shown in (f), the laser damage threshold increased in turn. The above results show that ion beam etching combined with oxygen ion implantation and post-annealing treatment can systematically and effectively eliminate the metal impurity defects, fragmented defects and oxygen-deficient structure defects of fused silica components, thus significantly improving the laser damage threshold of fused silica components.

[0028] Example 2

[0029] The size of the fused silica optical component was 30 mm × 30 mm × 4 mm. Part of the area of the fused silica component was shielded by polyimide tape. An argon ion beam with an energy of 600 eV, a beam current density of 1.39 mA / cm 2 and an incident angle of 70° was used to etch the surface of the component for 400 min. The emission electron current was 600 mA. The step height, i.e., the etching depth, at the boundary between the unetched area and the etched area was measured by a step profiler to be 13.30 μm. Then the etching rate of the ion beam on the fused silica component was 33.25 nm / min. The size of the fused silica component to be processed was 50 mm × 50 mm × 5 mm. The surface of the fused silica component was etched by rotation using the same ion beam parameters as those for etching rate calibration. Every time after etching 500 nm, the etching was stopped for 10 min, and an optical microscope was used to observe the fragmented defects on the surface until the fragmented defects were completely removed. The final etching depth was 5 μm. After ion beam etching, a high-purity ion implanter was used to implant oxygen ions on the surface of the component. The ion energy was 30 keV, and the fluence was 5 × 10 16 ions / cm 2After ion implantation, the fused silica component was subjected to subsequent annealing treatment in an oxygen atmosphere using a clean high-temperature tube furnace. The gas flow rate was 200 sccm, and it was heated to 500 °C at a heating rate of 15 °C / min and held for 6 h. Then, it was cooled to room temperature at a cooling rate of 10 °C / min. Finally, the annealed fused silica component was ultrasonically cleaned with deionized water and absolute ethanol, respectively, for 30 min each, and then naturally dried in a clean environment.

[0030] An optical microscope was used to in-situ observe the fragmentation-type defects during the ion beam etching process, as Figure 3 (a) and (b) show that after ion beam etching, the polished deposition layer was removed, exposing the fragmentation-type defects. After ion beam etching for 5 μm, the fragmentation-type defects were completely removed. The metal impurity distribution on the surface of the component before and after ion beam etching was measured using a time-of-flight secondary ion mass spectrometer, as Figure 3 (c) and (d) show that there were a large number of metal impurities on the surface before ion beam etching. After ion beam etching, the metal impurity content decreased sharply, indicating that ion beam etching can remove the metal impurity defects on the surface of the component. The EPR spectra of fused silica before and after ion implantation and annealing treatment were measured using an electron paramagnetic resonance spectrometer, as Figure 3 (e) shows that after ion implantation and subsequent annealing treatment, the concentration of oxygen vacancies decreased successively, indicating that oxygen ion implantation can recombine the oxygen-deficient structure defects and subsequent annealing treatment can further eliminate the oxygen-deficient structure defects on the surface and even in the material itself. The R:1 laser damage threshold of the fused silica component under different treatment procedures was measured using a Nd:YAG laser with a laser wavelength of 355 nm, as Figure 3 (f) shows that the laser damage threshold increased successively. The above results indicate that ion beam etching combined with oxygen ion implantation and subsequent annealing treatment can systematically and effectively eliminate the three types of precursors that induce laser damage in fused silica components: metal impurity defects, fragmentation-type defects, and oxygen-deficient structure defects, thereby significantly improving the laser damage resistance performance of fused silica components.

[0031] The above are only the preferred embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

Claims

1. A post-treatment method for a fused silica component with a high laser damage threshold, characterized in that, It includes the following steps: S1. Ion beam etching: Use a large-angle ion beam to etch the surface of the fused silica component to remove metal impurity defects and broken-type defects on the component surface; S2. Ion implantation: Perform oxygen ion implantation on the surface of the fused silica component after ion beam etching in step S1 to introduce oxygen ions and repair oxygen-deficient structure defects; S3. Post-annealing treatment: For the fused silica component after ion implantation in step S2, use a clean high-temperature tube furnace to perform subsequent annealing treatment on the fused silica component to further eliminate oxygen-deficient defects on the surface and in the material itself; S4. Cleaning of the fused silica component: Use deionized water and anhydrous ethanol to ultrasonically clean the fused silica component after annealing in step S3, with the cleaning time being 30 minutes for both, and then naturally dry it in a clean environment; The gas ion source used in step S1 is high-purity argon; the ion beam energy is 100 eV to 1500 eV; the beam current density is 0.28 mA / cm 2 ~1.91 mA / cm 2 ; the angle between the ion beam and the normal of the fused silica substrate is 60 o ~90 o ; a neutralizer is used to provide negatively charged electrons to neutralize the positively charged ion beam, and the emitted electron current is 100 mA to 900 mA; In step S1, in order to ensure uniform and effective removal of broken-type defects, during the etching process, the fused silica component is rotated for etching; in order to avoid stress generation, the fused silica component is etched intermittently, that is, for every 500 nm of etching depth, the etching is stopped for 10 minutes.

2. The post-treatment method of a fused silica component with a high laser damage threshold according to claim 1, characterized in that: Part of the fused silica component is shielded. Within a fixed time, based on the ion beam etching parameters, the fused silica component is etched to create a step, and then a profilometer is used to measure the step height, that is, the etching depth, at the boundary between the unetched area and the etched area. The etching rate of the fused silica component for different ion beam parameters is calculated based on the etching depth and the etching time used. In order to ensure the accuracy and reliability of the etching rate, the etching depth is greater than 10 μm.

3. The post-treatment method of a fused silica component with a high laser damage threshold according to claim 2, characterized in that: Based on the calibrated etching rate, accurately control the etching depth of the fused silica component. The final etching depth of the fused silica component depends on the distribution depth of the broken-type defects. In order to completely remove the broken-type defects, the fused silica component is iteratively etched with an ion beam, that is, after etching a certain depth, an optical microscope is used to observe the surface broken-type defects until the broken-type defects are completely removed, and then the etching is stopped.

4. The post-treatment method of a fused silica component with a high laser damage threshold according to claim 1, characterized in that: The gas ion source used in step S2 is high-purity oxygen; the ion implantation energy is 10 keV to 50 keV; the ion fluence is 1×10 16 ions / cm 2 ~3×10 17 ions / cm 2 ; It includes single and multiple injections under different ion energies and ion fluences.

5. The post-treatment method of a fused silica component with a high laser damage threshold according to claim 1, characterized in that: During the injection process in step S2, in order to avoid stress generation, the sample stage is cooled by circulating water.

6. The post-treatment method of a fused silica component with a high laser damage threshold according to claim 1, characterized in that: The atmosphere used in step S3 is high-purity oxygen, the oxygen flow rate is 100 sccm to 500 sccm, the annealing temperature is 300 °C to 900 °C, the annealing time is 0.5 h to 8 h. In order to avoid stress generation, the heating rate is controlled at 5 °C / min to 15 °C / min, and the cooling rate is controlled at 5 °C / min to 10 °C / min, and it is cooled to room temperature.

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