Laser cleaning pretreatment method for aluminum alloy components for preventing and controlling contamination of optical elements

Abstract

This invention discloses a laser-based clean pretreatment method for aluminum alloy components used in optical element contamination control, belonging to the field of laser beam precision machining and optical system cleanroom control technology. The method includes: assessing the presence of severe scratches, oil stains, and mechanical damage on the surface of the aluminum alloy structural component; performing surface pretreatment on the aluminum alloy structural component; fixing the pretreated aluminum alloy structural component in a vacuum or inert atmosphere treatment chamber, and using a pulsed laser to perform a full-coverage scanning irradiation of the surface to be protected; removing the laser-pretreated aluminum alloy structural component and performing post-processing in a clean environment to remove loose products from the surface, resulting in a laser-cleaned pretreated aluminum alloy structural component. This invention removes adsorbed gases while simultaneously strengthening the surface, thereby improving the laser damage resistance of the aluminum alloy structural component and providing an innovative and reliable solution for contamination source suppression in high-precision optical systems.

Description

Technical Field

[0001] This invention belongs to the field of laser beam precision machining and optical system clean control technology. More specifically, this invention relates to a laser clean pretreatment method for aluminum alloy components for the prevention and control of contamination in optical elements. Background Technology

[0002] In next-generation information technology equipment such as high-power laser devices and extreme ultraviolet lithography machines, the laser-induced damage threshold of optical components is a core bottleneck determining the system's output energy. The release of contaminants from structural materials under stray light irradiation is one of the main causes of damage to optical components. However, during machining, heat treatment, and surface treatment, aluminum alloys inevitably introduce and adsorb molecular contaminants such as hydrocarbons and moisture into their subsurface, burying micron- and nano-scale impurities or defects. When these aluminum alloy structural components are placed in extreme environments of high vacuum, high temperature, or long-term stray laser irradiation, their subsurface becomes a continuous source of contamination. The adsorbed molecular contaminants gradually desorb and are released, while impurities or defects in the subsurface may sputter metal or compound particles under the influence of heat or laser energy. These released contaminants migrate and deposit on the surface of adjacent optical components, leading to a decrease in the reflectivity / transmittance of the optical components and a significant reduction in the laser damage threshold, seriously threatening the reliability and lifespan of the entire high-precision optical system.

[0003] To address this challenge, scholars both domestically and internationally have conducted extensive research on optical contamination suppression technologies. For aluminum alloy structural components in optical systems, chemical etching removes surface materials and adhering contaminants through strong alkaline solutions. However, this method generates chemical waste, the etching depth and uniformity are difficult to control precisely, and it is a passive removal strategy, unable to handle deeply adsorbed contaminants. Mechanical polishing also cleans the surface by physically removing surface materials, but it may introduce new scratches or embed abrasive particles, and it is difficult to handle aluminum alloy structural components with complex morphologies. Vacuum high-temperature baking promotes the diffusion and escape of contaminants through prolonged high-temperature heating, but it is energy-intensive, time-consuming, and the high temperature may alter the microstructure and mechanical properties of the aluminum alloy. Surface coating technology attempts to construct a physical isolation layer on the aluminum alloy surface, but the adhesion strength, thermal compatibility, and durability under strong laser environments of the coating itself still face challenges, and coating failure may introduce new contamination sources. Most existing technologies focus on "post-treatment removal" or "physical isolation," failing to fundamentally intervene in the release kinetics of subsurface contaminants on aluminum alloys under subsequent high-intensity laser conditions. These technologies suffer from inherent limitations such as incomplete treatment, introduction of new risks, low efficiency, or limited applicability. Therefore, developing a technology that can proactively intervene, efficiently and thoroughly protect the service life of optical components without damaging the substrate is crucial for overcoming the bottleneck of long-term reliable operation of high-precision optical systems. 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 and other advantages according to the present invention, a laser cleaning pretreatment method for aluminum alloy components for contamination control of optical elements is provided, comprising the following steps: Step 1: Assess the surface of the aluminum alloy structural components for severe scratches, oil stains, and mechanical damage to ensure that the aluminum alloy structural components meet the usage requirements and laser pretreatment conditions; Step 2: Perform surface pretreatment on the aluminum alloy structural components from Step 1; Step 3: Fix the aluminum alloy structural component that has undergone surface pretreatment in Step 2 into a vacuum or inert atmosphere treatment chamber, and use a pulsed laser to perform a full-coverage scanning irradiation on the surface of the aluminum alloy structural component to be protected. Step 4: Take out the aluminum alloy structural parts that have undergone pulsed laser pretreatment in Step 3, and perform post-treatment in a clean environment to remove loose products on the surface of the aluminum alloy structural parts, and obtain the aluminum alloy structural parts after laser cleaning pretreatment.

[0006] Preferably, in step one, the aluminum alloy structural component is grade 6061.

[0007] Preferably, in step one, when evaluating the surface of the aluminum alloy structural component, a laser confocal microscope is used to observe the surface of the aluminum alloy structural component to ensure that the scratch depth is no greater than 5μm and the width is no greater than 20μm; at the same time, a 5~10wt% sodium hydroxide solution is used to clean the component at 50℃~70°C for 5min~10min.

[0008] Preferably, in step two, the surface treatment environment is a vacuum, and the vacuum pressure does not exceed 5 × 10⁻⁶. -3 Pa; During surface pretreatment, aluminum alloy structural parts are fixed in a non-metallic contact manner using tooling made of polytetrafluoroethylene.

[0009] Preferably, in step three, the energy density of the pulsed laser is lower than the laser-induced damage threshold of the aluminum alloy structural component, but higher than the thermal desorption threshold of organic pollutants on the subsurface of the aluminum alloy structural component.

[0010] Preferably, in step three, the wavelength of the pulsed laser is 1064nm, the pulse width is 5ns~15ns, and the spot diameter is 0.8cm~0.9cm; the laser energy density is set to 5%~30% of the laser-induced damage threshold of the corresponding aluminum alloy structural component; during scanning, the spot covers the surface of the aluminum alloy structural component with an overlap rate of 40%~60%.

[0011] Preferably, in step four, the specific method for post-processing the aluminum alloy structural parts in a clean environment includes: in a Class 100 clean environment, using a microfiber lint-free cloth soaked in anhydrous ethanol to gently wipe the laser-treated surface in one direction.

[0012] Preferably, the laser cleaning pretreatment method for aluminum alloy components used for contamination prevention and control of optical elements is used to improve the laser damage resistance of aluminum alloy components.

[0013] This invention offers at least the following beneficial effects: It provides a laser cleaning pretreatment method for aluminum alloy structural components used in optical element contamination control. By precisely controlling the laser energy within a specific area, it achieves active excitation of subsurface contaminants on the aluminum alloy structural components, ensuring the online service life of the optical components. Compared to traditional passive removal technologies such as chemical etching and mechanical polishing, this invention has advantages such as being non-contact, consumable-free, highly efficient, and applicable to complex-shaped aluminum alloy structural components. Furthermore, it can intervene at the source of contamination release mechanisms. Through the micro-area melting effect, this invention removes adsorbed gases while simultaneously strengthening the surface, thereby improving the laser damage resistance of the aluminum alloy structural components. This provides an innovative and reliable solution for contamination source suppression in high-precision optical systems.

[0014] 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

[0015] Figure 1 This is a process flow diagram of a laser cleaning pretreatment method for aluminum alloy components used in optical element contamination control according to the present invention. Figure 2 This is a schematic diagram illustrating the mechanism of a laser cleaning pretreatment method for aluminum alloy components used in optical element contamination control according to the present invention. Figure 3 This is a schematic diagram of the microstructure of the surface of an aluminum alloy structural component after laser cleaning pretreatment. Figure 4 Comparative morphological images of contaminants on the surface of a reflector before laser cleaning pretreatment; Figure 5 Comparative morphological images of contaminants on the surface of a reflector after laser cleaning pretreatment; Figure 6 A comparison of the laser-induced damage thresholds of the mirrors corresponding to the aluminum alloy structural components before and after laser pretreatment. Figure 7 The graph shows the impact of laser cleaning pretreatment on the laser-induced damage threshold and surface condition of aluminum alloy structural components. Detailed Implementation

[0016] 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.

[0017] 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. Example

[0018] like Figure 1 As shown, a laser cleaning pretreatment method for aluminum alloy components used for contamination control in optical elements includes the following steps: Step 1: Evaluation and Pretreatment of Aluminum Alloy Structural Components. First, the 3D morphology and defect inspection of the 6061 aluminum alloy structural components to be treated are performed. The surface is scanned using a laser confocal microscope to ensure that all scratches are no deeper than 5μm and no wider than 20μm. Simultaneously, metallographic microscopy is used to confirm that the surface of the aluminum alloy components is free of visible oil stains, fingerprints, watermarks, and macroscopic mechanical damage (such as chipping or pitting). For aluminum alloy structural components that meet the requirements, alkaline cleaning is performed: they are completely immersed in a 60°C, 8wt% sodium hydroxide solution for 10 minutes to saponify and decompose the grease on the surface of the aluminum alloy structural components. Immediately afterwards, a high-pressure deionized water gun at 1.5MPa is used to thoroughly rinse the aluminum alloy structural components for 2 minutes to completely remove residual alkaline solution and loose contaminants. Finally, a final rinse with high-purity water is performed, and the components are dried with high-purity nitrogen to obtain a clean and dry initial surface.

[0019] Step 2: Vacuum Chamber Preparation and Aluminum Alloy Structural Component Loading. Transfer the pre-treated aluminum alloy structural components into a dedicated laser pre-treatment vacuum chamber. Use a precision PTFE robotic arm or custom-made tooling to securely fix the aluminum alloy components onto the three-dimensional moving platform, ensuring that the surface to be treated is parallel to the laser scanning plane. After closing the chamber door, activate the vacuum system to evacuate and stabilize the internal pressure at ≤ 5 × 10⁻⁶. -3 The basic vacuum level is Pa.

[0020] Step 3: Laser Preprocessing Parameter Setting and Scanning. The pulsed laser is started via the electronic control system. The laser wavelength is 1064 nm, the pulse width is 10 ns, and the single-pulse energy is precisely adjusted using an attenuator. The laser beam is focused onto a circular Gaussian spot with a diameter of 0.886 cm. Based on the pre-calibrated aluminum alloy damage threshold (LIDT), the pulsed laser energy density is set within a safe window of 5% to 30% of the LIDT. For example, in this embodiment, for 6061 aluminum alloy structural parts (LIDT approximately 810 mJ / cm²), the energy density is set within this safe window. 2 The pulsed laser energy density was set to 71.3 mJ / cm². 2(Approximately 8.8% of its LIDT). A computer-controlled 3D moving platform scans the surface of the aluminum alloy structural component line by line along a predetermined path (e.g., a zigzag pattern) with a 50% overlap, ensuring uniform coverage of the entire area to be protected. The physical mechanism of this process is as follows: Figure 2 As shown in the schematic diagram, pulsed laser energy rapidly desorbs hydrocarbons adsorbed on the subsurface layer of the aluminum alloy structural component, which are then extracted in real time under vacuum. Simultaneously, the pulsed laser energy induces ultrathin (nanometer to submicron) micro-region melting and rapid solidification, dispersing or "welding" potential micro-impurities into the resolidified metal matrix. The surface condition of the treated aluminum alloy structural component is significantly altered, and its microstructure is as follows: Figure 3 As shown, it exhibits a more uniform and dense characteristic.

[0021] Step 4: Post-processing and Surface Inspection. After laser scanning is complete, turn off the laser and refill the vacuum chamber with clean air to atmospheric pressure. Remove the aluminum alloy structural component and, in a Class 100 clean bench, gently wipe the treated surface in one direction with a microfiber lint-free cloth soaked in high-purity anhydrous ethanol to remove any trace amounts of loose products that may have been generated due to material phase transitions. Then, dry the aluminum alloy structural component again with clean, dry air. Perform a preliminary inspection to check for uniformity of surface color and gloss, and for any visible abnormal burns.

[0022] A comparative verification experiment on the suppression effect was conducted. To quantitatively evaluate the effect of laser cleaning pretreatment on the aluminum alloy structural components in this embodiment, a comparative experiment was designed and executed. An aluminum alloy structural component that underwent laser cleaning pretreatment in steps one through four of this embodiment was taken as the "experimental group," and another aluminum alloy structural component from the same batch that underwent only evaluation and pretreatment in step one (without laser pretreatment) was taken as the "control group." These two aluminum alloy structural components were paired with a fused silica reflective mirror of known performance and identical initial state, coated with a high-reflectivity dielectric film (alternating hafnium dioxide and silicon dioxide films, with silicon dioxide as the outermost surface). Each pair (aluminum alloy structural component and reflector) was precisely fixed on a special fixture with the working surfaces facing each other, ensuring a distance of 10.0 ± 0.1 mm between the aluminum alloy structural component and the reflector. Both test pairs were simultaneously placed in a sealable simulated test chamber. A pulsed laser (wavelength 1064 nm, pulse width 10 ns, energy density fixed at 71.3 mJ / cm²) was used. 2 The surfaces of the aluminum alloy structural components in both groups were continuously irradiated at a grazing incidence angle of 2.8° for a total of 10,000 irradiations to simulate a long-term, low-flux stray light irradiation environment. During the irradiation process, the test chamber remained statically sealed without forced airflow disturbance.

[0023] After irradiation, the two sets of reflective mirrors were removed for testing. First, the surface morphology of the mirrors was observed using a laser confocal microscope. For example... Figure 4 , Figure 5 As shown, it can be clearly observed that the surface of the reflector opposite the control group (aluminum alloy) is scattered with a large number of aggregated contaminants of varying sizes and a small number of particles; while the surface of the reflector opposite the experimental group (laser pre-treated) aluminum alloy structural component is exceptionally clean, with a significant reduction in both the number and size of contaminants. This directly proves that laser pre-cleaning treatment can effectively suppress particulate sputtering and organic matter deposition in aluminum alloy structural components under irradiation. Subsequently, laser-induced damage threshold tests were performed on the two reflector mirrors. Figure 6 As shown, the test data indicates that the LIDT value of the mirror opposite the experimental group's aluminum alloy structural components decreased very little, almost equivalent to that of the uncontaminated original mirror; while the LIDT value of the mirror opposite the control group showed a significant decrease. This comprehensively verifies the clear effectiveness of the present invention in protecting optical components, focusing on the most crucial damage resistance performance of optical elements. Finally, the properties of the aluminum alloy structural components themselves after laser cleaning pretreatment were characterized. Figure 7 As shown, the LIDT of the aluminum alloy component was directly tested using a single-point, single-irradiation method, and its surface roughness was measured using a white light interferometer. The data indicate that after laser pretreatment with optimized parameters, both the LIDT and surface roughness of the aluminum alloy structural component were improved, achieving a simultaneous enhancement of surface strengthening and damage resistance.

[0024] The number of devices and processing scale described herein are for the purpose of simplifying the description of the invention. Applications, modifications, and variations of the invention will be readily apparent to those skilled in the art.

[0025] 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 laser cleaning pretreatment method for aluminum alloy components used for contamination control of optical elements, characterized in that, Includes the following steps: Step 1: Assess the surface of the aluminum alloy structural components for severe scratches, oil stains, and mechanical damage to ensure that the aluminum alloy structural components meet the usage requirements and laser pretreatment conditions; Step 2: Perform surface pretreatment on the aluminum alloy structural components from Step 1; Step 3: Fix the aluminum alloy structural component that has undergone surface pretreatment in Step 2 into a vacuum or inert atmosphere treatment chamber, and use a pulsed laser to perform a full-coverage scanning irradiation on the surface of the aluminum alloy structural component to be protected. Step 4: Take out the aluminum alloy structural parts that have undergone pulsed laser pretreatment in Step 3, and perform post-treatment in a clean environment to remove loose products on the surface of the aluminum alloy structural parts, and obtain the aluminum alloy structural parts after laser cleaning pretreatment.

2. The laser cleaning pretreatment method for aluminum alloy components for contamination control of optical elements as described in claim 1, characterized in that, In step one, the grade of the aluminum alloy structural component is 6061.

3. The laser cleaning pretreatment method for aluminum alloy components for contamination control of optical elements as described in claim 1, characterized in that, In step one, when evaluating the surface of the aluminum alloy structural parts, a laser confocal microscope is used to observe the surface of the aluminum alloy structural parts to ensure that the scratch depth is no greater than 5μm and the width is no greater than 20μm; at the same time, a 5~10wt% sodium hydroxide solution is used to clean the parts at 50℃~70°C for 5min~10min.

4. The laser cleaning pretreatment method for aluminum alloy components for contamination control of optical elements as described in claim 1, characterized in that, In step two, the surface treatment environment is a vacuum, with a vacuum pressure not exceeding 5 × 10⁻⁶. -3 Pa; During surface pretreatment, aluminum alloy structural parts are fixed in a non-metallic contact manner using tooling made of polytetrafluoroethylene.

5. The laser cleaning pretreatment method for aluminum alloy components for contamination control of optical elements as described in claim 1, characterized in that, In step three, the energy density of the pulsed laser is lower than the laser-induced damage threshold of the aluminum alloy structural component, but higher than the thermal desorption threshold of organic pollutants on the subsurface of the aluminum alloy structural component.

6. The laser cleaning pretreatment method for aluminum alloy components for contamination control of optical elements as described in claim 1, characterized in that, In step three, the wavelength of the pulsed laser is 1064nm, the pulse width is 5ns~15ns, and the spot diameter is 0.8cm~0.9cm; the laser energy density is set to 5%~30% of the laser-induced damage threshold of the corresponding aluminum alloy structural component; during scanning, the spot covers the entire surface of the aluminum alloy structural component with an overlap rate of 40%~60%.

7. The laser cleaning pretreatment method for aluminum alloy components for contamination control of optical elements as described in claim 1, characterized in that, In step four, the specific method for post-processing aluminum alloy structural parts in a clean environment includes: in a Class 100 clean environment, using a microfiber lint-free cloth soaked in anhydrous ethanol to gently wipe the laser-treated surface in one direction.

8. The laser cleaning pretreatment method for aluminum alloy components for contamination control of optical elements as described in claim 1, characterized in that, The laser cleaning pretreatment method for aluminum alloy components used for contamination control of optical elements is used to improve the laser damage resistance of aluminum alloy components.

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