A method for in-situ composite cleaning of large-aperture optical components using CO2 laser and low-pressure plasma

Abstract

The application discloses a method for cleaning a large-diameter optical element in situ by using a CO2 laser and low-pressure plasma, and comprises the following steps: cleaning a contaminated optical element by using a CO2 laser and low-pressure plasma combined cleaning system; designing a CO2 laser cleaning route, setting laser cleaning parameters, and cleaning the optical element by using the CO2 laser; setting low-pressure plasma cleaning parameters, and cleaning the optical element by using the low-pressure plasma; comparing performance parameters of the optical element before contamination, after contamination, after CO2 laser cleaning, and after low-pressure plasma cleaning; and optimizing the cleaning parameters to obtain optimal cleaning parameters for cleaning the large-diameter optical element in situ by using the CO2 laser and the low-pressure plasma. The application can realize high-efficiency and non-damage cleaning of the large-diameter optical element in situ, and effectively solves the problems of surface damage during laser cleaning of the precision optical element and low cleaning efficiency of the low-pressure plasma.

Description

Technical Field

[0001] This invention relates to, and more specifically, to a method for in-situ composite cleaning of large-aperture optical components using a CO2 laser and low-pressure plasma. Background Technology

[0002] In the long-term operation of large, precise, and complex optical systems such as synchrotron radiation light sources (SSRF), extreme ultraviolet lithography (EUV), the International Thermonuclear Experimental Reactor (ITER), spacecraft, and inertial confinement fusion devices (ICF), large-aperture optical elements are crucial components for transmission, frequency conversion, filtering, and focusing of the light source. To ensure the light source transmission quality of large-aperture optics, the optical system must maintain a vacuum state (10⁻⁶) for extended periods. -3 -10 -6 In a vacuum environment, structural components, sealing rubber rings, lubricating greases, and vacuum pumps used in optical systems gradually release molecular contaminants that desorb from their surfaces and volatilize into the environment. These contaminants then gradually diffuse, aggregate, settle, and adsorb onto the surfaces of large-aperture optical elements. After the optical system has been operating for a period of time, these deposits form on the surface of the optical elements, causing a significant decrease in their optical performance. Furthermore, changes in the surface profile of the optical elements further lead to a decrease in beam quality and an increase in surface field strength. As the performance indicators of large, precise, and complex optical systems continue to improve, the cleanliness requirements for the surfaces of large-aperture optical elements are becoming increasingly stringent, coupled with a gradual decrease in the stability of system operation.

[0003] Currently, clean maintenance of large-aperture optical components contaminated with carbon faces numerous challenges. On one hand, the large size and easily damaged surfaces of optical components make disassembly, transportation, cleaning, and installation difficult and time-consuming, significantly reducing the operational efficiency of the optical system. On the other hand, the complex and limited spatial environment of optical systems, the large size of optical components, and the susceptibility of optical surfaces to damage necessitate in-situ cleaning techniques that simultaneously achieve high cleaning efficiency and non-destructive cleaning. Therefore, scholars both domestically and internationally have continuously explored in-situ removal methods for organic contaminants on the surfaces of large-aperture optical components, innovatively proposing in-situ cleaning technologies such as laser cleaning, plasma cleaning, and ultraviolet-ozone cleaning. Laser cleaning, as a highly efficient method, can rapidly remove carbon contaminants from the surface of optical components through thermal absorption, but it is prone to over-cleaning and causing damage to the surface. Plasma cleaning, as a precision cleaning method, can remove trace amounts of carbon contaminants from the surface of optical components through physicochemical reactions, but its cleaning efficiency is low for large amounts of carbon contaminants. While ultraviolet-ozone cleaning also has some cleaning effect, its uncontrollable cleaning efficiency and process make it difficult to apply to the cleaning of precision optical component surfaces. Therefore, by combining the advantages of laser cleaning and plasma cleaning, it is theoretically possible to achieve in-situ cleaning of large-aperture optical systems in large, precision, and complex optical systems. However, understanding the principle of this composite cleaning, designing the method, selecting parameters, and planning the process are all very challenging. Summary of the Invention

[0004] One object of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0005] To achieve these objectives and other advantages of the present invention, a method for in-situ composite cleaning of large-aperture optical components using a CO2 laser-low-pressure plasma system is provided, comprising the following steps:

[0006] Step 1: Prepare optical component samples, perform contamination treatment on them, and measure the performance parameters of the optical components before and after contamination; install the contaminated optical components in a CO2 laser-low-pressure plasma composite cleaning system, and calibrate the position of the optical components by using an indicator light and camera detection.

[0007] Step 2: Design the CO2 laser cleaning route, set the laser cleaning parameters, and perform CO2 laser cleaning on the optical components;

[0008] Step 3: Measure the performance parameters of the optical components after CO2 laser cleaning and compare them with the performance parameters of the uncontaminated and contaminated optical components;

[0009] Step 4: Set the low-pressure plasma cleaning parameters and perform low-pressure plasma cleaning on the optical components after CO2 laser cleaning;

[0010] Step 5: Measure the performance parameters of the optical components after low-pressure plasma cleaning and compare them with the performance parameters of the optical components after uncontaminated, contaminated, and CO2 laser cleaning.

[0011] Step Six: By comparing the performance parameters of the optical components in Steps Three and Five, optimize the CO2 laser cleaning parameters in Step Two and the low-pressure plasma cleaning parameters in Step Five to obtain the optimal cleaning parameters for in-situ composite cleaning of large-aperture optical components using CO2 laser and low-pressure plasma. Perform composite cleaning on the large-aperture optical components according to the optimal cleaning parameters to achieve the best cleaning effect.

[0012] Preferably, the large-aperture optical element is a fused silica optical element coated with a silica antireflection film, with dimensions of 430mm×430mm×10mm, and the silica antireflection film has an antireflection band of 351nm.

[0013] Preferably, in step one, the optical element sample is prepared using the same substrate and coating process as the large-aperture optical element, and its size is 50mm×50mm×5mm.

[0014] Preferably, in step one, the contamination treatment simulates the heavily contaminated state of the optical element surface after long-term operation in a high vacuum environment. The specific method is as follows: the optical element is placed above a beaker containing dibutyl phthalate, and the beaker is heated to 100°C to accelerate the volatilization of pollutants and adsorption onto the surface of the optical element. Both sides of the optical element are contaminated for 40 seconds, and then left to stand for 6 hours after contamination.

[0015] Preferably, the performance parameters of the optical element include: transmittance, surface wettability, and microstructure.

[0016] Preferably, the performance parameters of the optical element are determined by: measuring transmittance using a spectrophotometer, measuring surface wettability using a contact angle tester, and measuring microstructure using an atomic force microscope.

[0017] Preferably, in step two, the CO2 laser cleaning route is as follows: a zigzag path is taken on the surface of the optical element; the laser cleaning parameters are as follows: the laser beam is a first-order diffraction beam, the pulse width is 5-50 μs, the working frequency is 2000 Hz, the peak power is 50 W, the moving speed is 80-100 mm / s, and the spot overlap rate is 0.3-0.7.

[0018] Preferably, in step four, the low-pressure plasma cleaning parameters are: discharge frequency of 10–30 kHz, power of 70–80 W, and cleaning time of 2–5 min.

[0019] Preferably, the CO2 laser-low-pressure plasma composite cleaning system includes:

[0020] A laser transmission pipe has a detachable sealing window installed on its front side. The laser transmission pipe and the sealing window together form a sealed environment. A slot for installing and fixing optical components is provided between the laser transmission pipe and the sealing window. The laser transmission pipe is installed on a two-dimensional moving platform, which allows the laser transmission pipe to move left and right and up and down.

[0021] The CCD camera is positioned relative to the laser transmission channel, so that it faces the front surface of the optical element.

[0022] A scanning galvanometer is positioned relative to the laser transmission channel, so that it faces the front surface of the optical element.

[0023] The He-Ne laser is used to output visible light. The visible light passes sequentially through a total reflection mirror, a beam splitter, a total reflection mirror, a beam expander, and a scanning galvanometer, and is focused onto the surface of an optical element as an indicator light.

[0024] A CO2 laser is used to output pulsed laser light. The pulsed laser light passes sequentially through an acousto-optic modulator, a beam splitter, a total reflection mirror, a beam expander, and a scanning galvanometer, and is focused onto the surface of an optical element to perform CO2 laser cleaning on the optical element.

[0025] An acousto-optic modulator, connected to a signal generator, is used to convert the pulsed laser output from a CO2 laser.

[0026] Four plasma discharge electrodes are arranged around the four sides of the sealed window;

[0027] A low-pressure plasma control system, which is connected to the laser transmission pipeline;

[0028] A low-pressure plasma discharge system connected to four plasma discharge electrodes;

[0029] The CO2 laser cleaning control system is connected to a CCD camera, a two-dimensional moving platform, a scanning galvanometer, a He-Ne laser, a signal generator, and a CO2 laser, respectively.

[0030] Preferably, the CO2 laser outputs pulsed laser with a wavelength of 10.6 μm, the laser beam is Gaussian in shape, the maximum output power is 100 W, and the operating frequency is 2000 Hz.

[0031] In this invention, the high vacuum environment is 10.-3 ~10 -6 Pa, the carbon pollutant used is dibutyl phthalate, which has an aromatic hydrocarbon structure and alkane branches, and the physicochemical properties of the pollutant are generally representative; the simulation of the heavily contaminated state of the optical element surface is achieved by fumigating with a beaker containing carbon pollutants, and the molecular pollutants will rapidly diffuse on the surface of the optical element to form a uniform carbon pollutant layer; after CO2 laser cleaning, the optical element needs to be placed in a clean sample box and left to stand for 6 hours to allow the residual carbon pollutants on the surface of the optical element to diffuse freely and reach an equilibrium state again, and then the optical element is reinstalled in the slot on the laser transmission pipeline. During the installation process, it is locked by a limiting structure to ensure that the optical element is installed in the same position every time.

[0032] This invention offers at least the following advantages: The CO2 laser-low-pressure plasma in-situ composite cleaning method for large-aperture optical components utilizes the thermal absorption effect of CO2 laser on the optical component to coarsely clean organic contaminants on the component surface, followed by fine cleaning through the physicochemical interaction between low-pressure plasma and the organic contaminants. This method improves the removal efficiency of organic contaminants from the surface of large-aperture optical components while avoiding the risk of surface damage. This composite cleaning method enables efficient and non-destructive in-situ cleaning of large-aperture optical components, unaffected by the component's shape, size, or surface coating material. It effectively solves the problems of easy surface damage during laser cleaning of precision optical components and low cleaning efficiency of low-pressure plasma, providing an active cleaning method for in-situ clean maintenance of large-aperture optical components in large, precise, and complex optical systems, ensuring the long-term, efficient, and stable operation of the optical system.

[0033] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0034] Figure 1 This is a top view schematic diagram of a CO2 laser-low-pressure plasma composite cleaning system according to the present invention;

[0035] Figure 2 A route diagram for CO2 laser cleaning of optical component surfaces;

[0036] Figure 3 The peak transmittance of the optical element at 351 nm under different states in the invention;

[0037] Figure 4 The surface wettability of the optical element under different states in this invention;

[0038] Figure 5 The microstructure of the optical element under different states in this invention;

[0039] In the figure, 1-optical element, 2-CO2 laser cleaning control system, 3-CCD camera, 4-two-dimensional moving platform, 5-scanning galvanometer, 6-He-Ne laser, 7-total reflection mirror, 8-beam splitter, 9-total reflection mirror, 10-beam expander, 11-signal generator, 12-CO2 laser, 13-acousto-optic modulator, 14-plasma discharge electrode, 15-laser transmission pipe, 16-low-pressure plasma control system, 17-low-pressure plasma discharge system, 18-sealed window. Detailed Implementation

[0040] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0041] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0042] Figure 1 A CO2 laser-low-pressure plasma composite cleaning system of the present invention is shown, comprising:

[0043] A laser transmission pipe 15 has a detachable sealing window 18 installed on its front side. The laser transmission pipe and the sealing window together form a sealed environment. A slot for installing and fixing optical element 1 is provided between the laser transmission pipe 15 and the sealing window 18. The laser transmission pipe 15 is connected to a two-dimensional moving platform 4, which allows the laser transmission pipe 15 to move left and right and up and down.

[0044] CCD camera 3 is positioned relative to laser transmission channel 15, so that it faces the front surface of optical element 1;

[0045] The scanning galvanometer 5 is positioned relative to the laser transmission channel 15, so that it faces the front surface of the optical element 1.

[0046] The He-Ne laser 6 is used to output visible light. The visible light passes sequentially through the total reflection mirror 7, the beam splitter 8, the total reflection mirror 9, the beam expander 10, and the scanning galvanometer 5, and is focused onto the surface of the optical element 1.

[0047] CO2 laser 12 is used to output pulsed laser. The pulsed laser passes sequentially through acousto-optic modulator 13, beam splitter 8, total reflection mirror 9, beam expander 10 and scanning galvanometer 5, and is focused on the surface of optical element 1.

[0048] An acousto-optic modulator 13 is connected to a signal generator 11;

[0049] Four plasma discharge electrodes 14 are arranged around the four sides of the sealed window 18;

[0050] A low-pressure plasma control system 16 is connected to a laser transmission pipe 15;

[0051] A low-pressure plasma discharge system 17 is connected to four plasma discharge electrodes 14.

[0052] The CO2 laser cleaning control system 2 is connected to the CCD camera 3, the two-dimensional moving platform 4, the scanning galvanometer 5, the He-Ne laser 6, the signal generator 11, and the CO2 laser 12 respectively.

[0053] Working principle:

[0054] (1) CO2 laser cleaning: The contaminated optical element 1 is installed in the slot on the laser transmission pipe 15 and locked by the limiting structure; the CO2 laser cleaning control system 2 is automatically initialized to reset the relative positions of all components; the CO2 laser cleaning control system 2 sends signals to the signal generator 11 and the CO2 laser 12, and the peak of the pulsed laser waveform output by the CO2 laser 12 is deflected into a first-order diffracted beam by the acousto-optic modulator 13, which enters the scanning galvanometer 5 after passing through the beam splitter 8, the total reflection mirror 9 and the beam expander 10, and is focused on the surface of the optical element 1; the CO2 laser cleaning control system 2 sends signals to the He-Ne laser 6, and the output visible light passes through the total reflection mirror 7, the beam splitter 8, the total reflection mirror 9 and the beam expander 10 in sequence before entering the scanning galvanometer 5 and being focused on the surface of the optical element 1. The coaxiality of the two beams is measured at the exit of the scanning galvanometer 5, and the beam position is adjusted by the total reflection mirror 7 to ensure the coaxiality of the two beams, where the He-Ne The visible light output from laser 6 is used as an indicator light, replacing the CO2 laser (main laser) during optical path debugging. This avoids damage to the surface of the optical element caused by continuous irradiation of the main laser during debugging. The CCD camera 3 takes pictures and images, and the position of the indicator light on the surface of the optical element 1 is observed on the computer monitor. After debugging, the CO2 laser is output for experimentation. Therefore, as a substitute light, the coaxiality of the two beams must be ensured. The CCD camera 3 is turned on by the CO2 laser cleaning control system 2 to confirm the coordinate position of the optical element 1. The CO2 laser cleaning control system 2 controls the two-dimensional moving platform 4 to move the optical element 1, which is installed on the laser transmission pipe 15, to the cleaning origin. The cleaning route is designed in the CO2 laser cleaning control system 2, and the moving speed and spot overlap rate are set. The two-dimensional moving platform 4 moves the laser transmission pipe 15 containing the optical element 1, and scans and cleans the surface of the optical element 1 according to the cleaning route starting from the cleaning origin.

[0055] (2) Low-pressure plasma cleaning: After CO2 laser cleaning, a vacuum chamber is formed by bolting the sealed window 18 to the laser transmission pipe 15 to achieve environmental sealing. The low-pressure plasma control system 16 is turned on, and the vacuum is evacuated to the set vacuum level. Clean air is used as the gas source. The discharge frequency, power and cleaning time are set. The four plasma discharge electrodes 14 are connected through the low-pressure plasma discharge system 17 to discharge and generate plasma for low-pressure plasma cleaning.

[0056] In the following embodiments, a typical fused silica antireflective film coated fused silica optical element in a large, precision and complex optical system is taken as the research object. The heavy contamination state of the optical element surface after long-term operation in a high vacuum environment is simulated to verify the method of CO2 laser-low pressure plasma in-situ composite cleaning of large-aperture optical elements of the present invention offline.

[0057] In the following embodiments, the transmittance, surface wettability, and micromorphology of the optical elements before and after contamination are characterized, reflecting the optical performance, surface cleanliness, and damage status of the optical elements, respectively.

[0058] In the following embodiments, the contaminated optical elements were placed in a CO2 laser-low-pressure plasma composite cleaning system for cleaning. The transmittance, surface wettability, and microstructure of the cleaned optical elements were characterized to evaluate the effectiveness of the composite cleaning technology of the present invention. In this embodiment, the large-aperture optical element (430mm×430mm×10mm) was replaced with a small-sized optical element (50mm×50mm×5mm) prepared by the same process, which facilitates the removal of the optical element after cleaning for offline characterization. The tested data were statistically averaged.

[0059] Example

[0060] A method for in-situ combined cleaning of large-aperture optical components using CO2 laser and low-pressure plasma includes the following steps:

[0061] Step 1: Place the fused silica substrate (50mm×50mm×5mm) in an ultrasonic cleaning tank for surface cleaning treatment, and then place it in a Class 100 clean room to air dry naturally.

[0062] Step 2: Place the dried fused silica substrate in a sol-gel liquid and deposit a silica antireflection film on the substrate using a dip-coating method. The antireflection band of the silica antireflection film is 351nm, resulting in an optical element. First, place it in a sealed container with ammonia for post-processing for 24 hours. Then, remove the optical element and place it in a sealed container with hexamethyldisilazane for post-processing for another 24 hours. 300mL of ammonia or hexamethyldisilazane is placed in a beaker within the sealed container.

[0063] Step 3: The processed optical components are tested for transmittance using a spectrophotometer. Only when the transmittance reaches 99.9% does it meet the usage standard. The wettability and microstructure of the optical component surface are then tested using a contact angle tester and an atomic force microscope.

[0064] Step 4: Organic contamination of optical components that meet the usage standards is carried out by fumigation: The optical components are placed above a beaker containing dibutyl phthalate. The beaker is heated to 100°C to accelerate the volatilization of pollutants and adsorption onto the surface of the optical components. This simulates the heavily contaminated state of the optical components after long-term operation in a high vacuum environment. Both sides of the optical components are contaminated for 40 seconds. After contamination, the components are left to stand for 6 hours to obtain the contaminated optical components. The transmittance is then tested, as well as the surface wettability and microstructure.

[0065] Step 5: Install the contaminated optical element 1 into the slot of the laser transmission pipe 15 of the CO2 laser-low pressure plasma composite cleaning system and lock it in place using the limiting structure; automatically initialize the CO2 laser cleaning control system 2 to reset the relative positions of all components.

[0066] Step 6: The CO2 laser cleaning control system 2 controls the He-Ne laser 6 to emit visible light with a wavelength of 632.8nm as an indicator light. After passing through the total reflection mirror 7, beam splitter 8 and total reflection mirror 9, and then through the beam expander 10, the light enters the scanning galvanometer 5 and irradiates the surface of the contaminated optical element. The CCD camera 3 takes pictures and images to determine the relative position of the indicator light. The position of the indicator light on the surface of the optical element in the field of view is observed on the computer monitor.

[0067] Step 7: Signals are sent to signal generator 11 and CO2 laser 12 through CO2 laser cleaning control system 2. The peak value of the pulsed laser waveform output by CO2 laser 12 is deflected into a first-order diffracted beam by acousto-optic modulator 13, resulting in a CO2 laser with a pulse width of 50μs, a frequency of 2000Hz, and a peak power of 50W. After passing through beam splitter 8, total reflection mirror 9, and beam expander 10, the laser enters scanning galvanometer 5. The Gaussian spot focused on the surface of the optical element is calculated according to 1 / e 2 The effective diameter was calculated to be 74 μm; the CO2 laser output pulsed laser with a wavelength of 10.6 μm, the laser beam is Gaussian in shape, the maximum output power of the CO2 laser is 100 W, and the operating frequency is 2000 Hz.

[0068] Step 8: The CO2 laser cleaning control system 2 simultaneously sends signals to the CO2 laser 12 and the He-Ne laser 6. The coaxiality of the two beams is measured at the exit of the scanning galvanometer 5, and the beam position is adjusted by the total reflection mirror 7 to ensure the coaxiality of the two beams. The visible light output from the He-Ne laser 6 is used as an indicator light to replace the CO2 laser (main laser) during optical path debugging, so as to avoid damage to the surface of optical components caused by the continuous irradiation of the main laser during the debugging process.

[0069] Step 9: Using the CO2 laser cleaning control system 2, activate the CCD camera 3 to confirm the coordinate position of the optical element 1. Then, using the CO2 laser cleaning control system 2, control the two-dimensional moving platform 4 to move the optical element 1, mounted on the laser transmission pipe 15, to the cleaning origin. The CO2 laser cleaning path for the optical element 1 is as follows: Figure 2 As shown, the cleaning route is designed in the CO2 laser cleaning control system 2. The laser transmission pipe 15 equipped with optical element 1 is moved by the two-dimensional moving platform 4, so that the laser starts from the cleaning origin and moves in a zigzag pattern on the surface of the optical element. The moving speed is set to 90 mm / s and the spot overlap rate is 0.5, so as to realize full-diameter scanning cleaning.

[0070] Step 10: Characterize the transmittance, surface wettability and microstructure of the optical components after CO2 laser cleaning, and compare the performance parameters with those of uncontaminated and contaminated optical components to determine the degree of CO2 laser cleaning.

[0071] Step 11: After CO2 laser cleaning, a vacuum chamber is formed by bolting the sealed window 18 to the laser transmission pipe 15 to achieve environmental sealing. The low-pressure plasma control system 16 is turned on to pump the sealed environment to 20Pa. Clean air is used as the gas source. The discharge frequency is set to 20kHz and the power is set to 75W. The four plasma discharge electrodes 14 are connected through the low-pressure plasma discharge system 17 to discharge and generate plasma to clean the optical components for 3 minutes.

[0072] Step 12: After low-pressure plasma cleaning, the optical element 1 is characterized by transmittance, surface wettability and microstructure. The performance parameters are compared with those of the uncontaminated, contaminated and CO2 laser-cleaned optical elements to determine the degree of low-pressure plasma cleaning.

[0073] Figure 3The figures represent the peak transmittance of the optical element at 351 nm under different conditions in this embodiment. The transmittance of the uncontaminated optical element reaches 99.9%, which meets the usage requirements of this invention. After carbon contamination, the transmittance of the optical element drops rapidly to 95.7%, severely reducing the beam transmission efficiency. After CO2 laser cleaning, the transmittance of the optical element recovers to 99.4%. Although the transmittance of the optical element has recovered significantly, trace amounts of carbon contaminants still remain on the surface, failing to meet the usage requirements. Finally, after CO2 laser cleaning followed by low-pressure plasma cleaning, the carbon contaminants on the surface of the optical element are completely removed, and the transmittance is fully restored.

[0074] Figure 4 To illustrate the surface wettability of the optical element under different conditions in this embodiment, the post-treated optical element surface exhibits superhydrophobic properties due to the presence of numerous silanyl methyl groups, resulting in a surface water contact angle of 119.1°. The hydrocarbon bonds in the alkane molecules of the carbon contaminants further enhance the hydrophobic properties of the contaminated optical element surface, increasing the surface water contact angle to 124.0°. After CO2 laser cleaning, most of the carbon contaminants on the optical element surface are removed, along with the removal of some silanyl methyl groups, reducing the surface water contact angle to 66.2°. Further treatment with low-pressure air plasma completely removes the carbon contaminants from the optical element surface, while simultaneously forming numerous hydrophilic groups such as carboxyl and hydroxyl groups, further reducing the surface water contact angle to 11.6°. Therefore, the degree of surface contaminant removal can be qualitatively determined by the change in the surface water contact angle of the optical element.

[0075] Figure 5 To illustrate the microstructure of the optical element under different conditions in this embodiment, atomic force microscopy revealed that the chemical film on the surface of the uncontaminated optical element has a loose and porous structure with a surface roughness of only 1.373 nm. After carbon contamination, the raised peaks on the surface became rounded, and the roughness increased to 5.488 nm. After CO2 laser cleaning, most of the contaminants on the surface of the optical element were removed without causing any damage to the surface, and the roughness recovered to 4.052 nm. After low-pressure air plasma cleaning, the carbon contaminants on the surface of the optical element were not only completely removed, but the loose and porous structure of the optical element surface was not damaged, and the roughness recovered to 1.391 nm.

[0076] In summary, through comparative analysis of transmittance, surface wettability, and microstructure, it can be seen that the cleaning parameters of this embodiment have excellent cleaning effect. Using the above cleaning process to clean large-aperture optical components can achieve efficient and non-destructive cleaning of large-aperture optical components.

[0077] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for in-situ composite cleaning of large-aperture optical components using CO2 laser and low-pressure plasma, characterized in that, Includes the following steps: Step 1: Prepare optical component samples, treat them for contamination, and measure the performance parameters of the optical components before and after contamination. The contaminated optical components were installed in a CO2 laser-low-pressure plasma composite cleaning system, and the position of the optical components was calibrated by indicator light and camera detection. The contamination treatment simulated the heavily contaminated state of the optical component surface after long-term operation in a high vacuum environment. The specific method was as follows: the optical component was placed above a beaker containing dibutyl phthalate, and the beaker was heated to 100°C to accelerate the volatilization of contaminants and adsorption onto the surface of the optical component. Both sides of the optical component were contaminated for 40 seconds, and then left to stand for 6 hours after contamination. Step 2: Design the CO2 laser cleaning route, set the laser cleaning parameters, and perform CO2 laser cleaning on the optical components. The laser cleaning parameters are: the laser beam is a first-order diffraction beam, the pulse width is 5~50μs, the working frequency is 2000Hz, the peak power is 50W, the moving speed is 80~100mm / s, and the spot overlap rate is 0.3~0.

7. Step 3: Measure the performance parameters of the optical components after CO2 laser cleaning and compare them with the performance parameters of the uncontaminated and contaminated optical components; Step 4: Set the low-pressure plasma cleaning parameters and perform low-pressure plasma cleaning on the optical components. The low-pressure plasma cleaning parameters are: discharge frequency of 10~30kHz, power of 70~80W, and cleaning time of 2~5min. Step 5: Measure the performance parameters of the optical components after low-pressure plasma cleaning and compare them with the performance parameters of the optical components after uncontaminated, contaminated, and CO2 laser cleaning. Step 6: By comparing the performance parameters of the optical components in Step 3 and Step 5, optimize the CO2 laser cleaning parameters in Step 2 and the low-pressure plasma cleaning parameters in Step 5 to obtain the optimal cleaning parameters for in-situ composite cleaning of large-aperture optical components using CO2 laser and low-pressure plasma. The large-aperture optical element is a fused silica optical element coated with a silica antireflection film, with dimensions of 430mm×430mm×10mm, and the antireflection band of the silica antireflection film is 351nm. The CO2 laser-low-pressure plasma composite cleaning system includes: A laser transmission pipe has a detachable sealing window installed on its front side. The laser transmission pipe and the sealing window together form a sealed environment. A slot for installing and fixing optical components is provided between the laser transmission pipe and the sealing window. The laser transmission pipe is installed on a two-dimensional moving platform, which allows the laser transmission pipe to move left and right and up and down. The CCD camera is positioned relative to the laser transmission channel, so that it faces the front surface of the optical element. A scanning galvanometer is positioned relative to the laser transmission channel, so that it faces the front surface of the optical element. The He-Ne laser is used to output visible light. The visible light passes sequentially through a total reflection mirror, a beam splitter, a total reflection mirror, a beam expander, and a scanning galvanometer, and is focused onto the surface of an optical element as an indicator light. A CO2 laser is used to output pulsed laser light. The pulsed laser light passes sequentially through an acousto-optic modulator, a beam splitter, a total reflection mirror, a beam expander, and a scanning galvanometer, and is focused onto the surface of an optical element to perform CO2 laser cleaning on the optical element. An acousto-optic modulator, connected to a signal generator, is used to convert the pulsed laser output from a CO2 laser. Four plasma discharge electrodes are arranged around the four sides of the sealed window; A low-pressure plasma control system, which is connected to the laser transmission pipeline; A low-pressure plasma discharge system connected to four plasma discharge electrodes; The CO2 laser cleaning control system is connected to the CCD camera, two-dimensional moving platform, scanning galvanometer, He-Ne laser, signal generator, and CO2 laser respectively. The CO2 laser outputs pulsed laser with a wavelength of 10.6 μm, the laser beam is Gaussian in shape, the maximum output power is 100 W, and the operating frequency is 2000 Hz.

2. The method for in-situ composite cleaning of large-aperture optical components using CO2 laser-low-pressure plasma as described in claim 1, characterized in that, In step one, the optical element sample is prepared using the same substrate and coating process as the large-aperture optical element, and its size is 50mm×50mm×5mm.

3. The method for in-situ composite cleaning of large-aperture optical components using CO2 laser-low-pressure plasma as described in claim 1, characterized in that... The performance parameters of the optical element include: transmittance, surface wettability, and microstructure.

4. The method for in-situ composite cleaning of large-aperture optical components using CO2 laser-low-pressure plasma as described in claim 3, characterized in that... The performance parameters of the optical element are determined by: measuring transmittance with a spectrophotometer, measuring surface wettability with a contact angle tester, and measuring microstructure with an atomic force microscope.

5. The method for in-situ composite cleaning of large-aperture optical components using CO2 laser-low-pressure plasma as described in claim 1, characterized in that... In step two, the CO2 laser cleaning route is as follows: a zigzag path is taken on the surface of the optical element.

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