Evaluation method for irradiation resistance of optical element at different depths

Abstract

The invention provides a method for evaluating irradiation resistance of an optical element at different depths. The evaluation method comprises the following steps: irradiating the optical element by using high-energy density laser to obtain film layer information; performing surface analysis on the optical element to obtain a fluorescence spectrum and an atomic force microscope image, and recording the number of typical defects; judging the surface quality of the optical element according to the irradiation etching depth, the average number of surface defects and the change of the number of defects before and after irradiation; performing micro-area mechanical property analysis on the membrane and the interface thereof, and judging the quality of the membrane and the interface thereof according to the abnormal fluctuation quantity and the displacement jump quantity of the stress-strain curve; and analyzing the substrate and the subsurface of the substrate, and judging the weak position of the optical element according to the fluorescence spectrum growth rate of the film, the substrate and the subsurface of the substrate. According to the method, laser irradiation etching and a spectral effect are matched with a high-precision local mechanical property analysis method, so that the irradiation resistance of the optical element at different depths is evaluated.

Description

Technical Field

[0001] The present invention relates to the technical field of ultraviolet laser materials, and in particular to a method for evaluating the radiation resistance performance of an optical element at different depths. Background Art

[0002] Deep ultraviolet light (usually referring to the wavelength range between 10 nm and 200 nm) has high energy and can penetrate many materials. Therefore, it has a wide range of applications in fields such as semiconductor manufacturing, biomedical imaging, material analysis, and scientific research. Deep ultraviolet optical elements can precisely control and transmit this high-energy light, which is crucial for improving the resolution of lithography technology, performing precise DNA analysis, and studying the microstructure of materials. With the progress of technology, the performance of deep ultraviolet optical elements has been continuously improved, which is of great significance for promoting innovation and development in related fields.

[0003] During the processing of optical elements, such as cutting, grinding, and polishing, due to the mechanical and physical effects and chemical effects on the optical elements, surface processing defects of the optical material will be caused, such as scratches, local damage pits, and a series of subsurface defects such as tiny cracks, dislocations, and vacancy defects generated below the surface layer. In the process of coating the optical element, defects such as poor bonding between the substrate and the film layer, pore and vacancy-like defects in the film layer, scratches, and impurity incorporation may occur. At the same time, the processing and storage processes of the optical element may also cause surface contamination of the optical element. The distribution of these defects in the optical element has a depth difference, and due to different processing parameters and material characteristics, the content and distribution of defects in different optical elements will also have certain differences. The possible defects in the above optical elements will cause light absorption and scattering effects, reduce the beam quality, deteriorate the local thermal field distribution, and may cause local deformation of the element, damage the film layer, etc., thereby endangering the entire optical system.

[0004] Currently, the main difficulties in the research on the radiation resistance performance of optical elements are as follows: 1) The related technologies of the classical damage threshold method in the infrared band mainly focus on accurately judging the damage threshold of optical elements, eliminating measurement errors caused by the environment, and optimizing the test device. However, the above methods cannot solve problems such as the non-equivalence of deep ultraviolet radiation photochemical damage and photothermal damage. Directly using the damage threshold method is still photothermal damage, which has a large difference from the actual photochemical damage state of optical elements in the deep ultraviolet band during actual service; 2) The radiation performance of optical elements, such as transmittance, is an overall performance parameter, and it is difficult to miniaturize the test area, and the influence of different positions of the optical element cannot be distinguished; 3) It is difficult to determine the weak positions of the optical element during the irradiation process, and it is impossible to provide data support for the optimization and iteration of processes such as optical material preparation, grinding, and polishing.

[0005] Therefore, improving the quality of optical components has always been an important direction in the field of ultraviolet lasers. Studying the responses of different depth ranges of optical components during irradiation and determining the changes during irradiation at different positions such as the substrate, surface, subsurface, film layer, and film layer interface will provide data support for improving the performance of the components. In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The object of the present invention is to provide a method for evaluating the radiation resistance performance of an optical component at different depths, which realizes the evaluation of the radiation resistance performance of the optical component at different depths by using laser irradiation etching and spectral effects in cooperation with a high-precision local mechanical property analysis method.

[0007] The present invention provides a method for evaluating the radiation resistance performance of an optical component at different depths, including the following steps:

[0008] S1: Irradiate the optical component with a high-energy density laser to obtain the film layer information of the optical component;

[0009] S2: Conduct surface analysis on the optical component to obtain the fluorescence spectrum and atomic force microscope image of the optical component, and record the number of typical defects;

[0010] S3: If there is a flat-topped peak in the visible light band in the fluorescence spectrum, judge the surface quality of the optical component according to at least one of the irradiation etching depth, the average number of surface defects, and the change in the number of defects before and after irradiation; otherwise, go to step S4;

[0011] S4: If the optical component is a coated component, go to step S5; otherwise, go to step S6;

[0012] S5: Conduct micro-area mechanical property analysis on the film and its interface of the optical component coating, and judge the quality of the film and its interface according to the number of abnormal fluctuations and the number of displacement jumps in the stress-strain curve;

[0013] S6: Conduct substrate and substrate subsurface analysis on the optical component, and judge the weak position of the optical component according to the growth rate of the fluorescence spectrum of the film, substrate, and substrate subsurface with the irradiation dose.

[0014] In step S1, the high energy density can be 1.0 - 1.2 times the plasma damage threshold, for example, 1 - 3 J / cm 2 ; the wavelength of the laser is 10 - 200 nm; monitor the wavelength and intensity of the plasma spectral lines generated by the spectrometer, qualitatively analyze the composition of the optical component, and then determine the main components of the optical component, whether there is a coating, and determine the thickness of each film layer according to the number of laser irradiation pulses.

[0015] In step S2, the surface analysis includes: using the focused spot of a laser to analyze the surface radiation resistance performance of the optical element; the wavelength of the laser is 10 - 200 nm, the irradiation uses a positive defocusing method, the repetition frequency is 100 - 500 Hz, and the multi-pulse plasma damage threshold Fths at this position of the optical element is measured. Irradiate the optical element with the energy density of this multi-pulse plasma damage threshold, and monitor the fluorescence spectrum of the optical element excited by the laser until the fluorescence spectrum curve is stable without change; judge the surface quality of the optical element according to whether there is a "bun-shaped peak" in the visible light band in the fluorescence spectrum. After irradiation, compare and observe the atomic force microscope images of the irradiated area and the non-irradiated area, record the number of each typical defect, and each typical defect includes nub (large-scale scratch-like defect) s, nub (contaminant) s, nub (bubble) s, etc. Combine the fluorescence results to determine the surface contamination, defect quantity and distribution of the optical element.

[0016] In step S3, judging the surface quality of the optical element includes the following steps:

[0017] S31: If it is irradiated thousands of times or the irradiation etching depth exceeds the film thickness of the optical element, it is difficult to remove the contaminants on the optical element, and it is not suitable for ultraviolet band applications with high quality requirements; otherwise, go to step S32;

[0018] S32: If the average number of surface defects is too large, such as nub (large-scale scratch-like defect) s in the irradiated area + nub (contaminant) s in the irradiated area + nub (bubble) s in the irradiated area ≥ 10, the surface quality of the optical element is poor and it is not suitable for ultraviolet band applications with high quality requirements; otherwise, go to step S33;

[0019] S33: If the change in the number of defects before and after irradiation is too large, such as [nub (large-scale scratch-like defect) s in the substrate + nub (contaminant) s in the substrate + nub (bubble) s in the substrate] - [nub (large-scale scratch-like defect) s in the irradiated area + nub (contaminant) s in the irradiated area + nub (bubble) s in the irradiated area] ≥ 5, the removable contamination on the surface of the optical element is serious, and the requirements for packaging and storing the optical element need to be improved; otherwise, go to step S4.

[0020] Step S5 further includes: analyzing the anti-irradiation performance of the optical element coating; the anti-irradiation performance analysis includes: irradiating in a laser positive defocus mode, irradiating the optical element with the multi-pulse plasma damage threshold as the energy density, the wavelength of the laser is 10 - 200 nm, the number of pulses is 50 - 500 times, monitoring the fluorescence spectrum excited by the laser of the optical element during the irradiation process, analyzing the peak positions and peak value changes of the significant changes in the fluorescence spectrum during the irradiation process, determining the types of optical response defects and the change amount with the irradiation dose, recording as ΔInt(characteristic peak 1)m, ΔInt(characteristic peak 2)m, ΔInt(characteristic peak 3)m, ΔInt(characteristic peak 4)m, etc., and quantifying the anti-irradiation performance of the optical element coating.

[0021] The micro-area mechanical property analysis of the film and its interface includes: using the nano-indentation method to test the response of the defects near the interface of the optical element to the small-range stress, measuring the stress to be 100 - 500 mN, the test depths are 1 / 3, 2 / 3, and 1.2 times of the interface depth, the number of tests is 5 - 15, analyzing the number of abnormal fluctuations nub(fluctuation)m, the number of displacement jumps nub(jump)mi of the test stress-strain curve and their corresponding depths, and determining the response fluctuations and interface bonding characteristics brought by the film defects.

[0022] Comparatively analyze the number of abnormal fluctuations nub(fluctuation)m and displacement jumps nub(jump)mi of the film and the film interface, and judge the quality of the film and its interface according to the number of abnormal fluctuations and displacement jumps of the stress-strain curve, specifically including:

[0023] S51: If the number of abnormal fluctuations is too high, the film contains more defects and is not suitable for ultraviolet band applications with high quality requirements; otherwise, go to step S52;

[0024] S52: If the number of displacement jumps is too high, such as nub(fluctuation)m accounting for more than 10% of the total number of tests, the film layer bonding force is poor, such as nub(jump)mi accounting for more than 3% of the total number of tests, it is not suitable for ultraviolet band applications with high quality requirements; otherwise, the film and the film interface quality are considered similar.

[0025] In step S6, the matrix analysis of the optical element includes: preparing a penetrating scratch on the surface of the optical element, with the depth of the scratch being, for example, 100 - 1000 μm; applying stress on both sides of the scratch of the optical element to cause the optical element to crack; using an optical microscope to find a crack-free facet at a position far from the scratch and the surface of the optical element (30 - 70% of the center of the optical element); irradiating the facet with a focused laser spot, where the wavelength of the laser is 10 - 200 nm; monitoring the fluorescence spectrum of the optical element excited by the laser; analyzing the corresponding peak positions and their peak heights and recording ΔInt(characteristic peak 1)bi, ΔInt(characteristic peak 2)bi, ΔInt(characteristic peak 3)bi, ΔInt(characteristic peak 4)bi, etc.; measuring the stress-strain curve of this area by means of nanoindentation and recording the number of abnormal fluctuations nub(fluctuation)b and whether there is a displacement mutation nub(sudden jump)b; judging the weak position of the optical element by the following method:

[0026] S61: If the growth rate of the fluorescence spectrum of the film with the irradiation dose is greater than that of the matrix, such as [ΔInt(characteristic peak 1)m, ΔInt(characteristic peak 2)m, ΔInt(characteristic peak 3)m, ΔInt(characteristic peak 4)m + ……] > [ΔInt(characteristic peak 1)b, ΔInt(characteristic peak 2)b, ΔInt(characteristic peak 3)b, ΔInt(characteristic peak 4)b + ……], then go to step S62; otherwise, the weak position of the optical element is located in the matrix;

[0027] S62: If the number of abnormal fluctuations and the number of displacement jumps are too high, such as nub(fluctuation)b and nub(sudden jump)b account for more than 3% of the total number of tests, then perform a matrix subsurface analysis on the optical element; otherwise, the weak position of the optical element is located in the matrix.

[0028] The matrix subsurface analysis of the optical element includes: using the negative defocusing method of the focused laser spot to focus the focus on the matrix subsurface position; irradiating the optical element with the energy density at the multi-pulse plasma damage threshold, where the wavelength of the laser is 10 - 200 nm, the number of pulses is 100 - 500 times, and the repetition frequency is 100 - 500 Hz; monitoring the fluorescence spectrum excited by the laser; analyzing the peak value and peak position changes of the fluorescence spectrum and recording them as ΔInt(characteristic peak 1)bi, ΔInt(characteristic peak 2)bi, ΔInt(characteristic peak 3)bi, ΔInt(characteristic peak 4)bi, etc.

[0029] Judge the position with the weakest radiation resistance of the optical element by the following method:

[0030] S63: If the growth rate of the fluorescence spectrum of the film / substrate with the irradiation dose is greater than that of the subsurface of the substrate, such as [ΔInt(Characteristic Peak 1)m, ΔInt(Characteristic Peak 2)m, ΔInt(Characteristic Peak 3)m, ΔInt(Characteristic Peak 4)m + ……] > [ΔInt(Characteristic Peak 1)bi, ΔInt(Characteristic Peak 2)bi, ΔInt(Characteristic Peak 3)bi, ΔInt(Characteristic Peak 4)bi + ……], then the position where the film / substrate is located is the position with the weakest anti-irradiation performance; otherwise, proceed to step S64;

[0031] S64: If the growth rate of the fluorescence spectrum of the film / substrate with the irradiation dose is similar to that of the subsurface, such as [ΔInt(Characteristic Peak 1)b, ΔInt(Characteristic Peak 2)b, ΔInt(Characteristic Peak 3)b, ΔInt(Characteristic Peak 4)b + ……] ≈ [ΔInt(Characteristic Peak 1)bi, ΔInt(Characteristic Peak 2)bi, ΔInt(Characteristic Peak 3)bi, ΔInt(Characteristic Peak 4)bi + ……], then the anti-irradiation performances of the film / substrate of the optical element and the subsurface of the substrate are similar; otherwise, the subsurface of the optical element substrate is the position with the weakest anti-irradiation performance.

[0032] In order to solve the problems that it is difficult to evaluate the radiation resistance performance of different positions such as the substrate, surface, subsurface, film layer, and film layer interface of optical elements, and it is difficult to screen out the weak links of optical elements, the present invention proposes a method for evaluating the radiation resistance performance of optical elements at different depths, which uses the etching and spectral effects of laser irradiation in cooperation with a high-precision local mechanical property analysis method to realize the evaluation of the radiation resistance performance of optical elements at different depths.

[0033] Different from the related technologies of the classical damage threshold method in the infrared band, which are dedicated to improving the accuracy of damage threshold testing, the method of the present invention can find the ultraviolet band optical response of defects at different depths of optical elements and the defect evolution law caused by irradiation, realize the decoupled analysis of the defect response of optical elements, determine the main weak positions of the radiation resistance of optical elements, and basically clarify the performance degradation law of radiation damage at different depths; the above can not only be used for the analysis of the radiation resistance of ultraviolet optical elements, but also for the analysis of the weak links of optical element damage in the laser optical path of other bands. The present invention finds the weak links at different depths of optical elements and the corresponding anti-irradiation performance evaluation method, providing experimental and data support for the quality improvement of optical elements. Description of the Drawings

[0034] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0035] Figure 1 It is a flowchart for evaluating the radiation resistance performance of an optical element at different depths;

[0036] Figure 2 It is the fluorescence spectrum of the optical element;

[0037] Figure 3 It is the atomic force microscope image of the optical element;

[0038] Figure 4 It is the stress-strain curve of the optical element at different depths. Specific Embodiments

[0039] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs.

[0040] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form also includes the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0041] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0042] Embodiment 1

[0043] As Figure 1 shown, the method for evaluating the radiation resistance performance of the optical element of this embodiment at different depths includes the following steps:

[0044] 1) Irradiate the optical element to be tested with a 193nm laser with a high energy density (1.0 - 1.2 times the plasma damage threshold, about 1.0 - 3 J / cm 2 ), use a spectrometer to monitor the wavelength and intensity of the plasma spectral lines, qualitatively analyze the composition of the optical element, determine the main components of the element and whether there is a coating, and determine the thickness of each film layer according to the number of laser irradiation pulses.

[0045] 2) Analyze the surface radiation resistance performance of the optical element using the focused spot of a 193 nm laser. The irradiation adopts a positive defocusing method, with a repetition frequency of 100 - 500 Hz, and measure the multi-pulse plasma damage threshold Fths at this position of the optical element. Irradiate the material with this threshold as the energy density, and monitor the fluorescence spectrum of the material excited by the 193 nm laser until the fluorescence spectrum curve is stable without change and there is no "bun-shaped peak" in the visible light band. After irradiation, compare and observe the atomic force microscope images of the irradiated area and the non-irradiated area to record the number of each typical defect, nub (large-scale scratch-like defects)s, nub (contaminants)s, nub (bubbles)s, ……, and combine with the fluorescence results to determine the quantity and distribution of surface contamination and defects of the optical element.

[0046] 3) If there is still a "bun-shaped peak" in the visible light band after irradiating thousands of times or when the irradiation etching depth exceeds the thickness of the composition of the first layer of coating of the optical element, it indicates that the contaminants on the optical element are difficult to remove and it is not suitable for high-quality ultraviolet band applications; otherwise, proceed to step 4).

[0047] 4) Judge the average number of surface defects of the optical element in 30 microscopic images. If nub (large-scale scratch-like defects)s in the irradiated area + nub (contaminants)s in the irradiated area + nub (bubbles)s in the irradiated area ≥ 10, it means the surface quality of the optical element is poor and it is not suitable for high-quality ultraviolet band applications; if [nub (large-scale scratch-like defects)s in the substrate + nub (contaminants)s in the substrate + nub (bubbles)s in the substrate] - [nub (large-scale scratch-like defects)s in the irradiated area + nub (contaminants)s in the irradiated area + nub (bubbles)s in the irradiated area] ≥ 5, it means the removable contamination on the surface of the optical element is serious and the requirements for the packaging and storage of the element should be improved; in other cases, proceed to step 5).

[0048] 5) Judge whether the optical element is a coated element. If it is a coated element, proceed to step 6); otherwise, proceed to step 11).

[0049] 6) Use the optical element with surface contamination cleaned by irradiation for the analysis of the anti-radiation performance of the film. Adopt the positive defocusing method of ultraviolet laser for irradiation, irradiate the material with Fths as the energy density, with the number of pulses being 50 - 500 times. Monitor the fluorescence spectrum of the material excited by the 193 nm laser during the irradiation process, analyze the peak positions and peak value changes of the significantly changed fluorescence spectrum during the irradiation process, determine the types of optical response defects and their change amounts with the irradiation dose, and record them as ΔInt (characteristic peak 1)m, ΔInt (characteristic peak 2)m, ΔInt (characteristic peak 3)m, ΔInt (characteristic peak 4)m, ……, and quantify the anti-radiation performance of the material at this depth.

[0050] 7) Use the irradiated optical element with surface contamination cleaned for the micro-mechanical property analysis of the film and its interface. Since it is difficult to visually evaluate the irradiation performance of the interface by laser method, the nano-indentation method is used to test the response of defects near the interface of the element to small-range stress. The measured stress is 100 - 500 mN, the test depth is 1 / 3, 2 / 3, and 1.2 times the interface depth, the number of tests is 5 - 15, and analyze the number of abnormal fluctuations nub(fluctuation)m, displacement jumps nub(jump)mi in the test stress-strain curve and their corresponding depths to determine the response fluctuations caused by film defects and the interface bonding characteristics.

[0051] 8) Compare and analyze the number of abnormal fluctuations nub(fluctuation)m and displacement jumps nub(jump)mi of the film and the film interface. If nub(fluctuation)m accounts for more than 10% of the total number of tests, the film contains more defects and is not suitable for applications in the ultraviolet band with high quality requirements; if nub(jump)mi accounts for more than 3% of the total number of tests, the bonding force of the film layer is poor and is not suitable for applications in the ultraviolet band with high quality requirements; otherwise, it is considered that the quality of the film and the film interface is similar and proceed to step 9).

[0052] 9) Use a nano-scratching device to prepare a through-scratch with a depth of 100 - 1000 μm on the surface of the optical element, apply stress on both sides of the scratch of the optical element to cause the element to crack, find a small plane without cracks at a position (30 - 70% of the element center) far from the scratch and the surface of the element in the cross-section using an optical microscope, irradiate this small plane with a focused spot of 193 nm laser, the irradiation uses a positive defocusing method, the repetition frequency is 100 - 500 Hz, irradiate the material with an energy density of Fths, monitor the fluorescence spectrum of the material excited by the 193 nm laser, analyze the corresponding peak positions and their peak heights and record ΔInt(characteristic peak 1)bi, ΔInt(characteristic peak 2)bi, ΔInt(characteristic peak 3)bi, ΔInt(characteristic peak 4)bi,.... Use the nano-indentation method to measure the stress-strain curve in this area and record the number of abnormal fluctuations nub(fluctuation)b and whether there is a displacement mutation nub(jump)b.

[0053] 10) Compare the growth rates of the fluorescence spectra of the film and the substrate of the optical element with the increase of the irradiation dose. If [ΔInt(characteristic peak 1)m, ΔInt(characteristic peak 2)m, ΔInt(characteristic peak 3)m, ΔInt(characteristic peak 4)m +....] > [ΔInt(characteristic peak 1)b, ΔInt(characteristic peak 2)b, ΔInt(characteristic peak 3)b, ΔInt(characteristic peak 4)b +....], and nub(fluctuation)b and nub(jump)b account for more than 3% of the total number of tests, the weak position of the element is at the substrate position; otherwise, proceed to step 11).

[0054] 11) Use the optically clean optical element with surface contamination for the subsurface of the substrate. Focus the focal spot of the 193 nm laser in a negative defocus manner on the subsurface position of the substrate. Use a short-focus focusing lens to minimize the damage to the film layer. Irradiate the material with an energy density of Fths, with the number of pulses being 100 - 500 times and the repetition frequency being 100 - 500 Hz. During the irradiation process, monitor the fluorescence spectrum of the material excited by the 193 nm laser, analyze the changes in the peak value and peak position of the fluorescence spectrum, and record them as ΔInt(Characteristic Peak 1)bi, ΔInt(Characteristic Peak 2)bi, ΔInt(Characteristic Peak 3)bi, ΔInt(Characteristic Peak 4)bi, …….

[0055] 12) Compare the growth rates of the fluorescence spectra of various defects in the optical element film (or the substrate) and the subsurface of the substrate with the irradiation dose. If [ΔInt(Characteristic Peak 1)m, ΔInt(Characteristic Peak 2)m, ΔInt(Characteristic Peak 3)m, ΔInt(Characteristic Peak 4)m + ……] > [ΔInt(Characteristic Peak 1)bi, ΔInt(Characteristic Peak 2)bi, ΔInt(Characteristic Peak 3)bi, ΔInt(Characteristic Peak 4)bi + ……], then the position where the element film is located is the position with the weakest radiation resistance, and determine the corresponding radiation resistance parameters; if [ΔInt(Characteristic Peak 1)b, ΔInt(Characteristic Peak 2)b, ΔInt(Characteristic Peak 3)b, ΔInt(Characteristic Peak 4)b + ……] ≈ [ΔInt(Characteristic Peak 1)bi, ΔInt(Characteristic Peak 2)bi, ΔInt(Characteristic Peak 3)bi, ΔInt(Characteristic Peak 4)bi + ……], then the radiation resistance of the optical element substrate and the subsurface of the substrate is similar; otherwise, the subsurface of the element substrate is the position with the weakest radiation resistance.

[0056] Example 2

[0057] Based on Example 1, this example takes the analysis of the radiation resistance of fused silica optical elements at different depths as an example, and the steps are as follows:

[0058] 1) Irradiate the fused silica optical element to be tested with a 193 nm laser with an energy density of 1.5 mJ / cm 2 Monitor the wavelength and intensity of the plasma spectral lines generated by the spectrometer, qualitatively analyze the composition of the optical element, and determine that the main component of the element is fused silica material and there is no coating.

[0059] 2) Use the focused spot of the 193 nm laser to analyze the surface radiation resistance of the optical element. The irradiation uses a positive defocus method, with a repetition frequency of 200 Hz. The multi-pulse plasma damage threshold at this position of the element is 1.27 mJ / cm 2 . Irradiate the material with this threshold as the energy density, and monitor the fluorescence spectrum of the material excited by the 193 nm laser (see Figure 2), after 500 irradiations, the fluorescence spectrum curve is stable without change, and there is no "bun-shaped peak" in the visible light band. After irradiation, the atomic force microscope images of the irradiated area and the non-irradiated area were observed and compared (see Figure 3 ), and the number of each typical defect, nub (large-scale scratch-like defect)s, nub (contaminant)s, nub (bubble)s, ……, was recorded. Combining with the fluorescence results, the quantity and distribution of surface contamination and defects of the optical element were determined. The results are shown in Table 1.

[0060] Table 1

[0061] nub (large-scale scratch-like defect) nub (contamination) nub (bubble / micropore) 1 1 5

[0062] 3) The total number of surface defects of this element is < 10, and the number of defects remains unchanged after irradiation.

[0063] 4) The optical element is a non-coated element;

[0064] 5) A through-scratch with a depth of 600 μm was prepared on the surface of the optical element using a nano-scratch device. Stress was applied on both sides of the scratch of the optical element to cause the element to crack. At a position far from the scratch and the surface of the element (30 - 70% of the element center) in the cross-section, a small flat surface without cracks was found using an optical microscope. The small flat surface was irradiated with a focused spot of 193 nm laser. The irradiation was in a positive defocus mode with a repetition frequency of 200 Hz, and the material was irradiated with an energy density of 1.27 mJ / cm 2 to monitor the fluorescence spectrum of the material excited by the 193 nm laser, analyze the corresponding peak positions and their peak heights, and record ΔInt(313nm)bi, ΔInt(363nm)bi, ΔInt(480nm)bi, ΔInt(650nm)bi, ……. The stress-strain curve of this area was measured using the nano-indentation method (see Figure 4 ), and the number of abnormal fluctuations nub (fluctuation)b and whether there is a displacement mutation nub (jump)b were recorded. The results are shown in Table 2 and Table 3.

[0065] Table 2

[0066] ΔInt(313nm)bi ΔInt(363nm)bi ΔInt(480nm)bi ΔInt(650nm)bi 5000 6000 1000 2000

[0067] Table 3

[0068] nub (fluctuation)b nub (abrupt change)b 0 2

[0069] 6) The optical element with surface contamination cleaned by irradiation was used for the subsurface of the substrate. The focused spot of the 193 nm laser was focused on the subsurface position of the substrate in a negative defocus mode. A short-focus focusing mirror was used to minimize the damage to the film layer, and with an energy density of 1.27 mJ / cm 2As the energy density irradiation material, the number of pulses is 100 - 500 times, and the repetition frequency is 100 - 500 Hz. During the irradiation process, the fluorescence spectrum excited by the 193 nm laser of the monitored material is analyzed, and the changes in the peak value and peak position of the fluorescence spectrum are recorded as ΔInt(characteristic peak 1)bi, ΔInt(characteristic peak 2)bi, ΔInt(characteristic peak 3)bi, ΔInt(characteristic peak 4)bi, …… The results are shown in Table 4.

[0070] Table 4

[0071] ΔInt(313nm)bi ΔInt(363nm)bi ΔInt(480nm)bi ΔInt(650nm)bi 260000 280000 2000 2500

[0072] 7) Compare the growth rates of the fluorescence spectra of various defects in the optical element matrix and the subsurface of the matrix with the irradiation dose. The sum of the growth amounts of the characteristic peak values of the matrix < the sum of the growth amounts of the characteristic peak values of the subsurface of the matrix. The subsurface of the element matrix is the position with the weakest anti-irradiation performance.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating the radiation resistance of an optical element at different depths, characterized in that: The steps include: S1: Use high energy density laser to irradiate optical elements to obtain the film information of optical elements; S2: Perform surface analysis on optical components, obtain fluorescence spectra and atomic force microscope images of optical components, and record the number of typical defects; S3: If the fluorescence spectrum has a mantou peak in the visible light band, the surface quality of the optical element is judged according to at least one of the irradiation etching depth, the average number of surface defects, and the change in the number of defects before and after irradiation; otherwise, proceed to step S4; S4: If the optical element is a coated element, proceed to step S5; Otherwise, proceed to step S6; S5: Analyze the micro-area mechanical properties of the optical element coating and its interface, and judge the quality of the film and its interface based on the number of abnormal fluctuations and displacement jumps in the stress-strain curve; S6: Analyze the substrate and substrate subsurface of the optical element, and determine the weak position of the optical element based on the fluorescence spectra of the film, substrate, and substrate subsurface increasing at the rate of irradiation dose.

2. The evaluation method according to claim 1, characterized in that: In step S1, the high energy density is 1-3 J / cm 2 ; The wavelength of the laser is 10-200nm; the film information includes whether there is coating and the film thickness.

3. The evaluation method according to claim 1, characterized in that: In step S2, the surface analysis includes: using a focused spot of a laser to analyze the radiation resistance of the surface of the optical element, the irradiation adopts a positive defocusing method with a repetition frequency of 100-500 Hz, and obtaining the multi-pulse plasma damage threshold of the optical element; irradiating the optical element with the multi-pulse plasma damage threshold as the energy density, and monitoring the fluorescence spectrum excited by the laser until the fluorescence spectrum curve is stable and unchanged.

4. The evaluation method according to claim 1, characterized in that: In step S2, the number of typical defects is recorded based on the atomic force microscope images of the irradiated area and the non-irradiated area, and the typical defects include at least one of large-scale defects such as scratches, contaminants and bubbles; the surface contamination of the optical element, the number and distribution of typical defects are determined by combining the fluorescence spectrum and atomic force microscope images of the optical element.

5. The evaluation method according to claim 1, characterized in that: In step S3, judging the surface quality of the optical element includes the following steps: S31: If the irradiation is performed for thousands of times or the irradiation etching depth exceeds the thickness of the optical element film layer, the optical element contaminants are difficult to remove and are not suitable for ultraviolet band applications with high quality requirements; otherwise, proceed to step S32; S32: If the average number of surface defects is too large, the surface quality of the optical element is poor and is not suitable for ultraviolet band applications with high quality requirements; otherwise, proceed to step S33; S33: If the number of defects before and after irradiation changes too much, the optical element surface is seriously removably contaminated, and the requirements for optical element packaging and storage need to be improved; otherwise, go to step S4.

6. The evaluation method according to claim 1, characterized in that: Step S5 also includes: analyzing the radiation resistance of the optical element coating; the radiation resistance analysis includes: irradiating with a laser positive defocus mode, irradiating the optical element with an energy density of a multi-pulse plasma damage threshold, with a pulse number of 50-500 times, monitoring the fluorescence spectrum excited by the laser, analyzing the peak position and peak value change of the fluorescence spectrum that changes significantly during the irradiation process, determining the type of optical response defects and the amount of change with the irradiation dose, and quantifying the radiation resistance of the optical element coating.

7. The evaluation method according to claim 1, characterized in that: In step S5, the micro-area mechanical properties analysis of the membrane and its interface includes: using the nanoindentation method to test the response of defects near the interface of the optical element to a small range of stress, the measured stress is 100-500mN, the test depth is 1 / 3, 2 / 3 and 1.2 times the interface depth, the number of tests is 5-15, and the number of abnormal fluctuations, the number of displacement jumps and their corresponding depths of the test stress-strain curve are analyzed to determine the response fluctuations caused by the membrane defects and the interface bonding characteristics.

8. The evaluation method according to claim 1, characterized in that: In step S5, judging the quality of the film and its interface according to the number of abnormal fluctuations and displacement jumps of the stress-strain curve includes: S51: If the number of abnormal fluctuations is too high, the film contains many defects and is not suitable for ultraviolet band applications with high quality requirements; otherwise, proceed to step S52; S52: If the number of displacement jumps is too high, the film bonding strength is poor and is not suitable for UV band applications with high quality requirements; otherwise, the quality of the film and the film interface is considered to be similar.

9. The evaluation method according to claim 1, characterized in that: In step S6, performing matrix analysis on the optical element includes: preparing a through scratch on the surface of the optical element, applying stress to both sides of the scratch of the optical element to crack the optical element, searching for a crack-free small plane at a position of the cross section far away from the scratch and the surface of the optical element by using an optical microscope, irradiating the small plane with a focused spot of laser, monitoring the fluorescence spectrum excited by the laser, and determining the weak position of the optical element by the following method: S61: If the fluorescence spectrum of the film increases at a greater rate than that of the substrate as the irradiation dose increases, then proceed to step S62; otherwise, the weak position of the optical element is located in the substrate; S62: If the number of abnormal fluctuations and the number of displacement jumps are too high, a substrate subsurface analysis is performed on the optical element; otherwise, the weak position of the optical element is located in the substrate.

10. The evaluation method according to claim 1, characterized in that: In step S6, performing a substrate subsurface analysis on the optical element includes: focusing the laser light spot on the substrate subsurface position by a negative defocusing method, irradiating the optical element with a multi-pulse plasma damage threshold as the energy density, the number of pulses is 100-500 times, the repetition frequency is 100-500 Hz, monitoring the fluorescence spectrum excited by the laser, and determining the position where the optical element has the weakest radiation resistance by the following method: S63: If the fluorescence spectrum of the film / substrate increases at a rate greater than that of the substrate subsurface as the radiation dose increases, the location of the film / substrate is the location with the weakest radiation resistance; otherwise, proceed to step S64; S64: If the fluorescence spectrum of the film / substrate increases at a rate similar to that of the subsurface as the radiation dose increases, the radiation resistance of the optical element film / substrate and the substrate subsurface are similar; otherwise, the optical element substrate subsurface is the weakest location in terms of radiation resistance.

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