Micro-area prefabrication method and selective repair method for femtosecond laser induced fused quartz surface oxygen vacancy defect and system of micro-area prefabrication method and selective repair method

Abstract

The invention discloses a femtosecond laser induced fused quartz surface oxygen vacancy defect micro-area prefabrication and selective repair method and system, and belongs to the field of laser precision machining and optical material modification. According to the method, irradiation parameters of femtosecond laser on the surface of fused quartz in an oxygen-containing atmosphere are controlled, and the nonlinear absorption effect of the femtosecond laser is utilized, so that two functions are realized: firstly, oxygen vacancy defects with quantitative concentration can be controllably prefabricated in a specified micro-area, and the problem that atomic-scale defects are difficult to position and characterize is solved; and 2, performing selective bonding repair on the positioned oxygen vacancy defect, so that the chemical composition of the defect area is recovered to be close to an ideal stoichiometric ratio. According to the system, a visual positioning module, a parameter mapping module and a cooperative control module are integrated, and full-automatic accurate operation is achieved. The surface roughness change of the area repaired through the method is smaller than 0.04 nm, the method has the advantages of being free of damage, controllable and high in precision, and an effective technical approach is provided for improving the laser damage threshold value of the fused quartz optical element.

Description

TECHNICAL FIELD

[0001] The present application relates to the fields of laser precision machining technology and optical material modification, and particularly relates to a method and system for micro-area preparation and selective repair of oxygen vacancy defects on a fused quartz surface induced by femtosecond laser. BACKGROUND

[0002] Fused quartz has become a key material for high-end optical systems such as high-power laser devices due to its excellent optical and thermodynamic properties. The performance limit of these systems is ultimately constrained by the laser-induced damage threshold of fused quartz optical elements. The intrinsic damage threshold of fused quartz can reach the order of 100 J / cm², but during the machining process based on mechanical rubbing removal, surface or subsurface defects (such as scratches, pits, etc.) and atomic-scale defects are inevitably introduced, which makes the actual damage threshold of the machined element much lower than the theoretical value, becoming a bottleneck problem restricting the improvement of the damage threshold of fused quartz elements. Among them, cracks, scratches, pits and other defects have been effectively inhibited with repeated precision machining and the application of non-contact machining methods. However, the precise positioning and characterization of atomic-scale defects such as oxygen vacancies make the study of damage mechanisms, non-destructive removal and selective repair of oxygen vacancy defects face great challenges, which seriously restricts the further improvement of the damage threshold of fused quartz high-power laser elements.

[0003] Traditional optical machining methods (such as mechanical polishing, chemical etching, etc.) can improve the surface topography, but it is difficult to accurately position and repair atomic-scale defects. In addition, oxygen vacancy defects are extremely small in size and sparse in distribution, and conventional characterization methods (such as optical microscopy, scanning electron microscopy, etc.) cannot achieve accurate positioning and quantitative analysis, which leads to major challenges in the study of defect damage mechanisms and targeted repair. In recent years, femtosecond laser machining technology has shown unique advantages in micro-nano machining, surface modification and defect repair due to its ultra-short pulse, ultra-high peak power and nonlinear absorption characteristics. Femtosecond laser can deposit energy in a very small area on the material surface in a very short time, inducing local chemical bond recombination and oxidation reaction, and almost no thermal affected zone, which provides the possibility for selective repair of atomic-scale defects.

[0004] However, there is still a lack of a method in the prior art that can systematically establish the correspondence between the femtosecond laser process parameters and the oxidation degree of the oxygen vacancy defects on the fused quartz surface, and an integrated technology solution for micro-area preparation, accurate control and non-destructive repair of oxygen vacancy defects has not been achieved. Therefore, it is of great significance to develop a high-precision, non-destructive process that can realize the positioning, control and repair of oxygen vacancy defects for improving the damage threshold of fused quartz elements and promoting the development of high-power laser technology. SUMMARY

[0005] To solve the problem that the surface oxygen vacancy defects of fused quartz optical elements are difficult to locate, characterize and repair in the prior art, the application provides a method and system for micro-preparation and selective repair of fused quartz surface oxygen vacancy defects induced by femtosecond laser.

[0006] To achieve the above-mentioned object, the technical solution of the application is as follows: Firstly, the application provides a method for micro-preparation of fused quartz surface oxygen vacancy defects induced by femtosecond laser, characterized in that the method introduces and quantitatively characterizes the oxygen vacancy defects at a specified position on the surface of fused quartz by regulating the local oxidation reaction induced by femtosecond laser, and specifically includes the following steps: (S1) Positioning and atmosphere establishment: place the polished fused quartz sample on a precision motion platform, and use a CCD vision system to position the surface of the sample to be processed on the focal plane of the focusing objective lens in an oxygen-containing atmosphere; (S2) Preparation parameter loading: set the femtosecond laser to output a laser beam with the following parameters: wavelength 532-1030 nm, pulse width 290-400 fs, single pulse energy density 0.4-1.2 J / cm², and repetition frequency 1-10 MHz; and set the scanning processing parameters: scanning speed 1-50 mm / s, and scanning line spacing 0.0005-0.005 mm; (S3) Controllable oxidation preparation: control the femtosecond laser beam to scan the selected micro area on the sample surface according to the preset path, use the local nonlinear absorption induced by the ultra-high peak power of the femtosecond laser to selectively break the Si-Si bond on the surface of the single crystal silicon, and promote the penetration and bonding of oxygen atoms in the environment, thereby forming a SiOX structure with different oxygen contents in the micro area, and realizing the controllable preparation of the spatial distribution and concentration of the oxygen vacancy defects, wherein X<2; (S4) Quantitative characterization of preparation effect: after processing, measure the oxygen-silicon atomic ratio of the micro area using X-ray photoelectron spectroscopy, directly confirm and characterize the oxygen vacancy defect concentration of the prepared area by the quantifiable increase of the oxygen-silicon atomic ratio relative to the intrinsic state of single crystal silicon, and record the corresponding relationship between the laser parameters, scanning parameters and the measured oxygen-silicon atomic ratio or non-chemical ratio x value, and establish a corresponding relationship database of "laser parameters-scanning parameters-oxygen vacancy concentration".

[0007] Secondly, the application also provides a selective repair method for fused quartz surface oxygen vacancy defects induced by femtosecond laser, characterized in that the method is based on the corresponding relationship database established in claim 1 to non-destructively repair the located oxygen vacancy defect area, and specifically includes the following steps: (R1) Defect localization: identify the oxygen vacancy defect area on the fused quartz surface to be repaired; (R2) Repair parameter matching and loading: according to the database, match and set the femtosecond laser repair parameters for the target repair degree; in the repair parameters, the single pulse energy density is 0.01-0.4 J / cm²; (R3) Selective bonding repair: in an oxygen-containing atmosphere, control the precise irradiation of the defect area by the femtosecond laser beam, use the local nonlinear absorption induced by its ultrafast characteristics to selectively excite the dangling bond of the defect site and react with the environmental oxygen, realize the conversion of Si-Si bond to Si-O bond, thereby repairing the oxygen vacancy, and the surrounding lattice structure is not affected by heat; (R4) Repair effect verification: use a white light interferometer to detect the repair area, and the surface roughness change needs to be less than 0.04 nm; and use X-ray photoelectron spectroscopy to verify that the oxygen-silicon atomic ratio in the area is restored to close to 2.0.

[0008] Further, the spot diameter of the femtosecond laser beam on the sample surface after the focusing objective lens is 12-30 μm.

[0009] Further, in step (R2), the preferred combination of the repair parameters is: wavelength 1030 nm, pulse width 290 fs, single pulse energy density 1.2 J / cm², repetition frequency 1 MHz, scanning speed 2 mm / s, and scanning line spacing 0.0025 mm.

[0010] Further, in step (S3), the gradient control of the oxygen vacancy defect concentration is realized by controlling the scanning times between 1 and 8.

[0011] Thirdly, the present application provides a femtosecond laser-induced fused quartz surface oxygen vacancy defect control and selective repair system for implementing the above method, characterized in that it comprises: a femtosecond laser for outputting femtosecond laser pulses with adjustable wavelength, pulse width, energy and frequency; a beam shaping and transmission module comprising, in sequence along the laser propagation direction: - an aperture diaphragm located at the output end of the femtosecond laser for spatial filtering; - an expander lens group located immediately after the aperture diaphragm for expanding and collimating the laser beam; - a mirror group comprising multiple mirrors arranged in the optical path at a preset angle for changing the direction of beam transmission; - a polarization control element arranged after the mirror group and before the focusing objective lens for adjusting the polarization state of the beam; a focusing objective with its optical axis coaxially aligned with the exit beam of the beam shaping and delivery module, for converging the laser beam to the sample surface to form a high energy density spot; a three-dimensional precision motion platform, located right below the focusing objective or within its working distance, for carrying and moving the sample in X, Y, Z directions; a CCD camera, coupled with the optical path of the focusing objective, for realizing real-time coaxial or paraxial imaging of the sample surface; a computer control system, electrically connected with the femtosecond laser, the three-dimensional precision motion platform and the CCD camera respectively, and configured to: (v) store and manage the database of "laser parameter - scanning parameter - oxygen vacancy concentration" correspondence; (vi) identify the sample surface features or defect locations according to the images collected by the CCD camera, and drive the three-dimensional precision motion platform to move the target area to the laser focal point; (vii) in the pre-preparation mode, receive the target defect concentration and distribution instructions, automatically retrieve the corresponding laser parameters and scanning path parameters from the database, and synchronously control the femtosecond laser and the three-dimensional precision motion platform to perform processing; (viii) in the repair mode, receive the positioned defect coordinates and target repair degree instructions, automatically match the repair parameter set, and control the components to perform selective repair processing.

[0012] Further, it further comprises a controllable atmosphere cover for providing and maintaining air or oxygen atmosphere during processing.

[0013] Fourthly, the present application also provides a method for improving the laser-induced damage threshold of fused quartz optical elements, characterized in that it comprises: (A) using the micro-region pre-preparation method to pre-prepare a standard oxygen vacancy defect array in the non-critical regions of the element surface; (B) using the laser-induced damage test system to test the damage threshold of each defect in the pre-prepared defect array, and establishing a "oxygen vacancy concentration - damage threshold" correlation model; (C) using the selective repair method, according to the model established in step (B), positioning and repairing the oxygen vacancy defects in the critical working area of the element whose damage threshold is lower than the preset value.

[0014] Compared with the prior art, the technical effects of the present application are as follows: 1) By femtosecond laser to induce oxidation on the sample surface, by adjusting the laser wavelength, pulse width, repetition frequency, energy density and other parameters, the corresponding relationship between process parameters and surface oxidation degree is accurately established, the micro-area pre-preparation and non-destructive repair of oxygen vacancy defects in fused quartz strong light components are realized, and the surface of the processed area is smooth, and the roughness Ra is less than 0.04 nm, which shows that the process is non-damaging to the substrate.

[0015] 2) The super-high peak power of femtosecond pulse can induce local nonlinear absorption, promote atomic-scale recombination and bond repair of defect sites, and the surrounding lattice structure is almost not affected by heat, which overcomes the difficulty of accurate control and selective repair of atomic-scale oxygen vacancy defects in fused quartz strong light components. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present application, the following will briefly introduce the drawings needed in the implementation.

[0017] Figure 1 The process diagram of femtosecond laser-induced fused quartz surface oxygen vacancy defect control and repair provided by the present application is shown. Figure 2 The device structure diagram of the femtosecond laser-induced fused quartz surface oxygen vacancy defect control and repair system of the present application is shown. Figure 3 The schematic diagram of white light interferometer detecting the surface roughness of the modified area is shown, wherein a is the scanning twice surface topography diagram, b is the scanning four times surface topography diagram, c is the scanning six times surface topography diagram, and d is the scanning eight times surface topography diagram.

[0018] Figure 4 The schematic diagram of X-ray photoelectron spectroscopy (XPS) analysis of the change of micro-area oxygen silicon non-stoichiometric ratio x under different scanning times is shown. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the protection scope of the present application. Those skilled in the art can make several adjustments and modifications to the following embodiments based on the prior art, combined with the concept of the present application, and these adjustments and modifications should also be regarded as the protection scope of the present application.

[0020] As shown in Figure 1 A femtosecond laser-induced fused quartz surface oxygen vacancy defect control and selective repair method, comprising the following steps: S1 Preparation stage: 1. Materials and experimental equipment Polished fused silica or single crystal silicon wafer is selected as the substrate.

[0021] The laser is a femtosecond laser, the output beam wavelength is 532-1030 nm, the pulse width is 290-400 fs, the single pulse energy density is 0.01-1.2 J / cm², and the repetition frequency is 1-10 MHz.

[0022] The outgoing beam passes through the aperture diaphragm 2 and the beam expander group 3 in turn. Adjust the beam expander group to make the output beam a collimated beam, and the beam diameter is slightly smaller than the clear aperture of the subsequent mirror.

[0023] Adjust the pitch angle of the mirrors 4-8 in turn to ensure that the beam is transmitted along the designed light path and finally incident to the center of the objective lens 10. Use a shearing interferometer or a beam quality analyzer to check the beam wavefront and collimation before the objective lens.

[0024] Connect the CCD camera 13 to the computer control system 12, and observe the image through the software interface. Place a high-reflectivity silicon wafer near the focal plane of the objective lens as a focusing target, and use the software to control the Z-axis movement of the three-dimensional precision motion platform 11, and combine the image clarity to accurately calibrate the focal point position of the objective lens in the platform coordinate system.

[0025] 2. Environmental conditions The laboratory needs to maintain a clean environment to avoid dust interference with laser focusing.

[0026] Select air or oxygen as the experimental atmosphere.

[0027] S2 Implementation phase Place the polished fused silica or single crystal silicon sample on the precision motion platform, ensure that the sample surface is level, and the surface inclination is ≤0.01 0 .

[0028] Use the CCD camera to complete the focusing of the sample, and ensure that the sample is located at the focal plane of the objective lens.

[0029] The user sets the target defect concentration level (low, medium, high). The system automatically recommends and loads the following three groups of parameter combinations to the execution unit according to the pre-stored "laser parameter-scan parameter-oxygen vacancy concentration" mapping relationship database: Low concentration area (A area): single pulse energy density 0.5 J / cm², scanning speed 20 mm / s, scanning line spacing 0.003 mm, scanning times 1.

[0030] Medium concentration area (B area): single pulse energy density 0.8 J / cm², scanning speed 10 mm / s, scanning line spacing 0.0015 mm, scanning times 3.

[0031] High concentration area (C area): single pulse energy density 1.0 J / cm², scanning speed 5 mm / s, scanning line spacing 0.001 mm, scanning times 5 times.

[0032] Using the real-time image of the CCD camera 13, the processing starting area of the sample surface is selected in the software.

[0033] Click to start, the system first drives the three-dimensional precision motion platform 11 to move the A area under the laser focus. Then, the control and data processing module synchronously triggers the femtosecond laser 1 to emit light and the platform to move according to the preset "grating path", completing the processing of the A area.

[0034] After processing, the laser is automatically turned off, the platform moves to the B area according to the preset coordinates, and the laser is started again to complete the processing of the B area, and the C area is the same. The whole process is fully automatic, without manual intervention of laser start and stop and parameter switching.

[0035] S3 post-processing stage After processing, turn off the laser, return the precision motion platform to zero, and take off the sample.

[0036] As shown in Figure 3 , the white light interferometer is used to detect the surface roughness Ra<0.04 nm of the substrate and the pre-prepared micro area, to ensure that the processing area is not damaged.

[0037] As shown in Figure 4 , the X-ray photoelectron spectroscopy (XPS) is used to analyze the chemical composition of the substrate and the surface of the pre-prepared micro area, and it is found that with the increase of scanning times, the oxygen-silicon ratio gradually increases, and the non-stoichiometric ratio x increases from about 0.07 to about 1.5, realizing the accurate control of the oxidation degree.

[0038] The present application has the following technical effects: In view of the core challenge that oxygen vacancy defects are difficult to locate due to atomic scale, the present application realizes the pre-preparation and non-destructive repair technology of the fused quartz surface oxygen vacancy micro area, which provides a new technical approach for repairing atomic-level defects such as oxygen vacancies on the surface of strong light elements. This technology solves the problem of difficult positioning of atomic-level defects such as oxygen vacancies through micro-preparation, and realizes non-destructive repair of oxygen vacancy defects through femtosecond laser, forming a technical closed loop of positioning first and then repairing, which provides an effective solution to improve the damage threshold of fused quartz elements.

[0039] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the above specific embodiments, and those skilled in the art can make various modifications or modifications within the scope of the claims, which does not affect the essential content of the present application.

Claims

1. A method for micro-fabrication of femtosecond laser induced fused silica surface oxygen-vacancy defects, characterized in that, The method can controllably introduce and quantitatively characterize oxygen vacancy defects at specified positions on the fused quartz surface by regulating the local oxidation reaction induced by femtosecond laser, and comprises the following steps: (S1) positioning and atmosphere establishment: place the polished fused quartz sample on a precision motion platform, and use a CCD vision system to position the surface to be treated of the sample in the focal plane of the focusing objective lens in an oxygen-containing atmosphere; (S2) pre-preparation parameter loading: set the output laser beam of the femtosecond laser to have the following parameters: wavelength 532-1030 nm, pulse width 290-400 fs, single pulse energy density 0.4-1.2 J / cm², and repetition frequency 1-10 MHz; and set the scanning processing parameters: scanning speed 1-50 mm / s, and scanning line spacing 0.0005-0.005 mm; (S3) Controllable oxidation pre-preparation: controlling the femtosecond laser beam to scan the selected micro area on the sample surface according to the preset path, using the local nonlinear absorption induced by the ultra-high peak power of the femtosecond laser to selectively break the Si-Si bond on the single crystal silicon surface, and promote the oxygen atoms in the environment to penetrate and bond, thereby forming SiO X structure, realizing the controllable pre-preparation of the spatial distribution and concentration of oxygen vacancy defects, wherein X<2; (S4) pre-preparation effect quantitative characterization: after processing, use X-ray photoelectron spectroscopy to measure the oxygen-silicon atomic ratio of the micro area, and directly confirm and characterize the oxygen vacancy defect concentration of the pre-prepared area by the quantifiable increase of the oxygen-silicon atomic ratio relative to the intrinsic state of single crystal silicon, and record the correspondence between the laser parameters, scanning parameters and the measured oxygen-silicon atomic ratio or non-stoichiometric ratio x value, and establish a corresponding relationship database of "laser parameters-scanning parameters-oxygen vacancy concentration".

2. A method for selective repair of femtosecond laser induced fused silica surface oxygen-vacancy defects, characterized by, Based on the corresponding relationship database established in claim 1, the method performs non-destructive repair on the positioned oxygen vacancy defect area, and comprises the following steps: (R1) defect positioning: identify the oxygen vacancy defect area to be repaired on the fused quartz surface; (R2) repair parameter matching and loading: according to the database, match and set the femtosecond laser repair parameters for the target repair degree; in the repair parameters, the single pulse energy density is 0.01-0.4 J / cm²; (R3) selective bonding repair: in an oxygen-containing atmosphere, control the precise irradiation of the femtosecond laser beam on the defect area, selectively excite the dangling bond of the defect site and react with the ambient oxygen by using the local nonlinear absorption induced by the ultrafast characteristics of the femtosecond laser beam, realize the conversion of Si-Si bond to Si-O bond, and thus repair the oxygen vacancy without affecting the surrounding lattice structure by heat; (R4) repair effect verification: use a white light interferometer to detect the repair area, and the surface roughness change needs to be less than 0.04 nm; and use X-ray photoelectron spectroscopy to verify that the oxygen-silicon atomic ratio of the area is restored to close to 2.

0.

3. The method according to claim 1 or 2, characterized in that, The spot diameter of the focused femtosecond laser beam on the sample surface is 12-30 μm.

4. The method of claim 2, wherein, In step (R2), the preferred combination of the repair parameters is: wavelength 1030 nm, pulse width 290 fs, single pulse energy density 1.2 J / cm², repetition frequency 1 MHz, scanning speed 2 mm / s, and scanning line spacing 0.0025 mm.

5. The method of claim 1, wherein, In step (S3), the scanning times are controlled to be between 1 and 8 to realize gradient control of the oxygen vacancy defect concentration.

6. A femtosecond laser-induced fused silica surface oxygen-vacancy defect modulation and selective repair system for implementing the method of any one of claims 1-5. It comprises: a femtosecond laser for outputting femtosecond laser pulses with adjustable wavelength, pulse width, energy and frequency; a beam shaping and transmission module comprising, in sequence along the direction of laser propagation: - an aperture stop (2) located at the output end of the femtosecond laser (1) for spatial filtering; - an expander lens group (3) located immediately after the aperture stop (2) for beam expansion and collimation; - a mirror group (4-8) comprising multiple mirrors arranged at a preset angle in the optical path for changing the direction of light transmission; - a polarization control element (9) located after the mirror group and before the focusing objective lens (10) for adjusting the polarization state of the light beam; a focusing objective lens (10) whose optical axis is coaxially aligned with the outgoing light beam of the light shaping and transmission module, for converging the laser beam to the sample surface to form a high-energy density spot; a three-dimensional precision motion platform (11) located directly below or within the working distance of the focusing objective lens (10) for carrying and moving the sample in X, Y, and Z directions; a CCD camera (13) coupled with the optical path of the focusing objective lens (10) for realizing coaxial or paraxial real-time imaging of the sample surface; a computer control system (12) electrically connected to the femtosecond laser (1), the three-dimensional precision motion platform (11), and the CCD camera (13), and configured to: (i) store and manage the "laser parameter-scan parameter-oxygen vacancy concentration" correspondence database; (ii) identify the sample surface features or defect locations according to the images collected by the CCD camera (13), and drive the three-dimensional precision motion platform (11) to move the target area to the laser focal point; (iii) in the pre-preparation mode, receive the target defect concentration and distribution instructions, automatically retrieve the corresponding laser parameters and scan path parameters from the database, and simultaneously control the femtosecond laser (1) and the three-dimensional precision motion platform (11) to perform processing; (iv) in the repair mode, receive the positioned defect coordinates and target repair degree instructions, automatically match the repair parameter set, and control the components to perform selective repair processing.

7. The femtosecond laser-induced fused silica surface oxygen-vacancy defect modulation and selective repair system of claim 6, wherein, It also includes a controllable atmosphere cover for providing and maintaining an air or oxygen atmosphere during processing.

8. A method of increasing the laser-induced damage threshold of a fused silica optical element, comprising, It includes: (A) using the micro-region pre-preparation method of claim 1 to pre-prepare a standard oxygen vacancy defect array in the non-critical regions of the element surface; (B) using the laser-induced damage test system of claim 6 or 7 to test the damage threshold of each defect in the pre-prepared defect array and establish an "oxygen vacancy concentration-damage threshold" correlation model; (C) using the selective repair method of claim 2 to locate and repair the oxygen vacancy defects in the critical working area of the element whose damage threshold is lower than the preset value according to the model established in step (B).

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