A laser cleaning method for improving the damage threshold of fused quartz components

Abstract

A laser cleaning method for improving the damage threshold of fused quartz components includes: first, using an optical microscope and a fluorescence confocal microscope to detect the distribution and depth of surface and subsurface contamination defects; then using a stress birefringence instrument to measure the thermal stress at different cleaning depths; then, using specific parameters to perform near-thermal stress-free laser cleaning to remove surface and subsurface contamination and structural defects of the component. This process can achieve uniform cleaning without damaging the roughness of the component; finally, using deionized water to ultrasonically clean the fused quartz component. The present invention is simple to operate and low-cost. Only laser cleaning is required to effectively remove defects and contamination, thereby achieving uniform cleaning without damaging the roughness under near-stress-free conditions and significantly improving the damage threshold of the fused quartz component. This method expands the application scenarios of laser processing and is of great significance for improving the damage threshold of components in high-power laser systems.

Description

Technical Field

[0001] The invention belongs to the field of optical element processing and manufacturing, and in particular to a laser cleaning method for improving the damage threshold of a fused quartz element. Background Art

[0002] In modern optical manufacturing, fused silica glass, due to its wide bandgap, is the material of choice for core components such as windows, focusing lenses, and diffraction gratings in most current high-power laser systems. However, as the demand for laser output energy continues to increase in high-power laser systems, the current mainstream contact grinding and polishing methods for fused silica glass processing can produce defects and contamination such as cracks, scratches, and impurities on the processed surface, severely shortening the service life of the components. Although domestic and foreign scholars currently use hydrofluoric acid, plasma, and ion beams for surface cleaning, these methods introduce reaction product deposition and ion contamination on the component surface, are costly and complex, and cannot meet the damage threshold requirements of existing optical components. Therefore, it is necessary to develop a method to remove surface defects and contamination. Laser cleaning is a relatively economical non-contact processing method that does not introduce surface defects or polishing impurities. It has inherent advantages in controlling processing defects such as scratches and cracks. However, laser cleaning technology can severely damage the roughness and introduce thermal stress. Therefore, there is currently no report on the use of laser cleaning to achieve processing without destroying the roughness of components under nearly thermal stress-free conditions, while at the same time improving the damage threshold of components. Therefore, the development of new theories and processes to achieve laser cleaning of fused quartz materials is of great significance for improving the damage threshold of fused quartz components and thus ensuring the smooth operation of high-power laser systems.

[0003] Patent document CN109570151A discloses a device and cleaning method for liquid flow ultrasonic composite assisted laser cleaning of optical components. This method achieves laser cleaning under low stress by using liquid flow ultrasonic assisted laser cleaning, which can avoid unnecessary damage and improve the performance of optical components. The disadvantage of this process solution is that it cannot guarantee the surface roughness accuracy after laser cleaning, and can only remove surface contamination, and cannot perform variable depth removal based on the distribution of defects and contamination, which has great limitations on the removal of contamination. At the same time, this problem is also a problem that exists in the vast majority of laser cleaning patents. It only removes surface contamination and cannot remove sub-surface defects, thereby limiting the improvement of the laser damage threshold of the component material.

[0004] Patent document CN114149180A discloses a processing method for improving the damage threshold of fused quartz components. In this technical solution, plasma processing is used to remove defects on the material surface, thereby improving the laser damage threshold of the component. The disadvantages of this solution are that the components processed by plasma will produce new oxides, which will become secondary contamination; in addition, the surface roughness of the components after plasma processing will be severely deteriorated; at the same time, compared with laser cleaning equipment, plasma processing equipment is relatively expensive. These three disadvantages have limited the development of plasma processing technology in improving the damage threshold of optical components, and therefore it has not been widely used in the field of processing high damage threshold components. Summary of the Invention

[0005] The purpose of this invention is to propose a laser cleaning method for improving the damage threshold of fused silica components. This method controls the laser cleaning depth under specific parameters, achieving uniform cleaning without damaging the surface roughness under near-thermal stress-free conditions, and significantly improving the damage threshold of fused silica components. This method is simple to operate and low-cost, expanding the application scenarios of laser processing and having significant significance for improving the damage threshold of components in high-power laser systems.

[0006] The technical solutions of the present invention are as follows:

[0007] A laser cleaning method for improving the damage threshold of fused quartz components is characterized by:

[0008] 1) Using optical microscopy and fluorescence confocal microscopy to detect the range and depth distribution of surface and subsurface contamination defects, so as to carry out targeted and precise cleaning;

[0009] 2) Use a stress birefringence instrument to measure the thermal stress at different cleaning depths to ensure that the cleaning process does not significantly introduce thermal stress;

[0010] 3) Nearly stress-free variable-depth laser cleaning under specific parameters: The fused quartz component is fixed on a three-dimensional mobile platform, and the laser is placed at a distance of 35mm-40mm from the component for processing. The laser cleaning depth is varied by controlling the pulse width, thereby precisely removing defects and contamination at different depths. The laser cleaning process is performed on the fused quartz component according to the above parameters until the laser beam completes the surface cleaning of the fused quartz component. This parameter ensures that the roughness is not damaged after cleaning.

[0011] 4) Ultrasonic cleaning of fused quartz components: First rinse with deionized water, then ultrasonically treat in pure water at a temperature of 20°C-30°C for 10-15 minutes, then rinse with deionized water, and finally dry on a clean bench to obtain the ultrasonically cleaned fused quartz components;

[0012] 5) Damage Threshold Test: A 1-on-1 damage threshold test was performed on laser-cleaned fused silica components according to ISO 21254. The test laser wavelength was 355 nm, the pulse width was 8.3 ns, and the frequency was 10 Hz.

[0013] In the variable depth laser cleaning under specific parameters in step 2), as a further improvement of the present invention, the laser power is set to 26.5 W, the frequency is set to 95 kHz, the scanning speed is set to 100 mm / s, the scanning path spacing in the x-direction and the y-direction is set to 25.5 μm, and the scanning path is set to a grid path; the pulse width is adjusted by an acousto-optic modulator, and its value is 55 μs-65 μs, thereby controlling the laser cleaning depth to less than 200 nm, thereby avoiding the generation of thermal stress and the destruction of roughness.

[0014] Compared with the prior art, the technical effects of the present invention are as follows:

[0015] Laser cleaning removes surface and subsurface contamination and defects, achieving uniform cleaning without damaging roughness under near-stress-free conditions and significantly improving the damage threshold of fused silica components. This method is simple to operate and low-cost, expanding the application scenarios of laser processing and having significant significance for improving the damage threshold of components in high-power laser systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A flowchart of the processing method for improving the damage threshold of a fused silica component according to the present invention;

[0017] Figure 2 A schematic diagram of a processing method for improving the damage threshold of a fused quartz component according to the present invention;

[0018] Figure 3 The roughness comparison of the fused quartz component before and after laser cleaning, where a is the initial roughness and b is the roughness after laser cleaning.

[0019] Figure 4 Comparison of thermal stress before and after laser cleaning of fused quartz components, where a is the initial thermal stress and b is the thermal stress after laser cleaning.

[0020] Figure 5 Comparison of the damage threshold of a fused silica component before and after laser cleaning. DETAILED DESCRIPTION

[0021] The laser cleaning method for improving the damage threshold of fused quartz components is described in detail below with reference to the accompanying drawings and embodiments, but this should not limit the scope of protection of the present invention.

[0022] The parameters of this embodiment are set as follows: laser power is set to 26.5 W, laser frequency is set to 95 kHz, scanning speed is set to 100 mm / s, path spacing in the x-direction and y-direction is set to 25.5 μm, beam radius is set to 150 μm, pulse width range is set to between 55 μs and 65 μs, and the workpiece to be processed is a square fused quartz plane workpiece with a side length of 30 mm and a thickness of 6 mm.

[0023] A laser cleaning method for improving the damage threshold of fused quartz components, the processing flow chart is as follows Figure 1 As shown in the figure, the method includes the following steps:

[0024] 1) First, use an optical microscope to observe the distribution of surface contamination and defects. Then, use a fluorescence confocal microscope to detect the range and depth distribution of subsurface contamination and defects. These two detection methods can fully demonstrate the distribution of surface and subsurface defects and contamination.

[0025] 2) Using a stress birefringence instrument to measure thermal stress at different cleaning depths, this ensures that no significant thermal stress is introduced during the cleaning process. When the cleaning depth is less than 200 nm, no residual thermal stress is generated.

[0026] 3) Variable depth laser cleaning under specific parameters: Since the fused quartz component is fixed on a three-dimensional mobile platform, the laser is placed at a distance of 35mm-40mm from the component for processing. The laser cleaning depth is changed by controlling the pulse width, thereby achieving the removal of defects and contamination at different depths. The laser needs to be preheated for 30 minutes before laser cleaning. The cleaning process is carried out according to the above parameters until the laser beam completes the cleaning of the surface of the fused quartz component. The laser cleaning equipment is shown in the figure below. Figure 2 As shown;

[0027] 4) Ultrasonic cleaning of fused quartz components: First rinse with deionized water, then ultrasonically treat in pure water at a temperature of 20°C-30°C for 10-15 minutes, then rinse again with deionized water, and finally dry on a clean bench to obtain the ultrasonically cleaned fused quartz components. The pretreatment environment is Class 1000 clean.

[0028] 5) Damage Threshold Test: A 1-on-1 damage threshold test was performed on laser-cleaned fused silica components according to ISO 21254. The test laser wavelength was 355 nm, the pulse width was 8.3 ns, and the frequency was 10 Hz.

[0029] The roughness of the fused quartz element processed by the method of the present invention was tested using a 4D optical profilometer (NanoCam Sq, 4D Technology). The test size was 0.2 mm × 0.2 mm. The results are as follows: Figure 3As shown in FIG. 1 , (a) is the roughness of the fused quartz component before processing using the method of the present invention, and (b) is the roughness of the fused quartz component after processing using the method of the present invention. The thermal stress of the fused quartz component processed by the method of the present invention is tested using a stress birefringence instrument (StrainMatic M4 / 150.10, ILIS Gmbh). The results are shown in FIG. Figure 4 Figure 2 shows the thermal stress of a fused quartz component before processing using the method of the present invention, with (a) showing the thermal stress of the component before and after processing using the method of the present invention, and (b) showing the thermal stress of the component after processing using the method of the present invention. The results show that the RMS roughness of the fused quartz component changes from 0.968 nm before processing to 1.032 nm, and the thermal stress changes from 0.52 nm / cm before processing to 0.53 nm / cm. The processing method of the present invention, under near-stress-free conditions, does not damage the roughness of the fused quartz component.

[0030] Then, the fused quartz components before and after processing by the method of the present invention were subjected to a 1 on 1 damage threshold test according to the international standard ISO21254. Figure 5 As shown in the figure, the fused silica component before and after laser cleaning has a 0% probability damage threshold of 17.1 J / cm 2 Increased to 25.5J / cm 2 , 100% probability damage threshold from 39.3J / cm 2 Increased to 47.9J / cm 2 The processing results observed in the examples prove that the invention has very significant practical effects.

[0031] Laser cleaning removes surface and subsurface contamination and defects, achieving uniform cleaning without damaging roughness under near-stress-free conditions and significantly improving the damage threshold of fused silica components. This method is simple to operate and low-cost, expanding the application scenarios of laser processing and having significant significance for improving the damage threshold of components in high-power laser systems.

Claims

1. A laser cleaning method for improving the damage threshold of fused quartz components, characterized in that: include: S1. Clean the surface and subsurface contamination defects according to the scope and depth distribution of the defects detected by optical microscopy and fluorescence confocal microscopy; S2. Use a stress birefringence instrument to measure thermal stress at different cleaning depths to ensure that the cleaning process does not introduce significant thermal stress. S3. Nearly stress-free, variable-depth laser cleaning under specific parameters: A fused quartz component is mounted on a three-dimensional moving platform, and the laser is positioned 35mm-40mm from the component for processing. The laser cleaning depth is varied by controlling the pulse width to remove defects and contamination at varying depths. The laser cleaning process continues according to these parameters until the laser beam completely cleans the surface of the fused quartz component. These parameters ensure that the roughness remains intact after cleaning. The near-stress-free variable-depth laser cleaning under specific parameters was performed with a laser power of 26.5W, a frequency of 95kHz, a scanning speed of 100mm / s, a scanning path spacing of 25.5μm in the x- and y-directions, and a grating scanning path. The pulse width was adjusted by an acousto-optic modulator, with a value of 55μs-65μs, thereby controlling the laser cleaning depth to less than 200nm, thereby avoiding the generation of thermal stress and damage to the roughness. S4. Ultrasonic cleaning of fused quartz components: First rinse with deionized water, then ultrasonically treat in pure water at a temperature of 20-30°C for 10-15 minutes, then rinse again with deionized water, and finally dry on a clean bench to obtain the ultrasonically cleaned fused quartz components.

2. The laser cleaning method for improving the damage threshold of fused silica components according to claim 1, characterized in that: Also included is S5. Damage Threshold Test: 1-on-1 damage threshold testing of laser-cleaned fused silica components according to ISO 21254, using a 355nm laser wavelength, 8.3ns pulse width, and 10Hz frequency.

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