阅读说明：本技术 一种预测光学元件表面激光损伤性能的方法和系统 (Method and system for predicting laser damage performance of surface of optical element ) 是由 石兆华 王凤蕊 刘红婕 吴之清 邵婷 夏汉定 周晓燕 邓青华 孙来喜 黄进 叶鑫 于 2019-12-02 设计创作，主要内容包括：本发明涉及一种预测光学元件表面激光损伤性能的方法和系统,通过选取标准光学元件；获取所述标准光学元件的吸收性缺陷分布特性,得到不同吸收水平的缺陷密度；获取损伤性能；损伤性能包括损伤阈值和损伤密度；采用Spearman相关性分析法,确定标准光学元件的不同吸收水平的缺陷密度中与损伤性能相关性最高的缺陷密度,得到各所述损伤性能对应的缺陷密度,并建立损伤性能与其对应的缺陷密度之间的关联曲线,作为标准曲线；获取待检测光学元件的缺陷密度,根据所述标准曲线,确定所述待检测光学元件的损伤性能。本发明提供的预测光学元件表面激光损伤性能的方法和系统,能够在不损坏光学元件的基础上,提高光学元件损伤性能的评估准确性。(The invention relates to a method and a system for predicting laser damage performance of the surface of an optical element, wherein a standard optical element is selected; acquiring the distribution characteristics of the absorption defects of the standard optical element to obtain defect densities with different absorption levels; obtaining damage performance; the damage performance includes a damage threshold and a damage density; determining the defect density with the highest correlation with the damage performance in the defect densities of different absorption levels of the standard optical element by adopting a Spearman correlation analysis method to obtain the defect density corresponding to each damage performance, and establishing a correlation curve between the damage performance and the corresponding defect density as a standard curve; and acquiring the defect density of the optical element to be detected, and determining the damage performance of the optical element to be detected according to the standard curve. The method and the system for predicting the laser damage performance of the surface of the optical element can improve the evaluation accuracy of the damage performance of the optical element on the basis of not damaging the optical element.)

1. A method for predicting laser damage performance of a surface of an optical element, comprising:

selecting a standard optical element;

acquiring the distribution characteristics of the absorption defects of the standard optical element to obtain defect densities with different absorption levels;

obtaining damage performance; the damage performance comprises a damage threshold and a damage density;

determining the defect density with the highest correlation with the damage performance in the defect densities of different absorption levels of the standard optical element by adopting a Spearman correlation analysis method to obtain the defect density corresponding to each damage performance, and establishing a correlation curve between the damage performance and the corresponding defect density as a standard curve;

and acquiring the defect density of the optical element to be detected, and determining the damage performance of the optical element to be detected according to the standard curve.

2. The method as claimed in claim 1, wherein the standard optical element has a surface treatment process identical to that of the optical element to be measured.

3. The method of claim 1, wherein the obtaining the damage performance comprises:

irradiating the standard optical element by adopting laser with different grades until the standard optical element is damaged;

testing the standard optical element for a damage threshold;

detecting the distribution condition of the damage points in the damage area to obtain the damage density;

and acquiring the damage performance of the standard optical element according to the damage threshold and the damage density.

4. The method as claimed in claim 1, wherein the method for predicting laser damage performance of the surface of the optical element is characterized in that the photothermal common path interference technology is adopted to test the weak absorption coefficient of the surface of the standard optical element, so as to obtain the absorption defect distribution characteristics of the standard optical element, and obtain the defect densities of different absorption levels.

5. The method of claim 1, wherein the calibration curve is obtained using a plurality of the calibration optical elements.

6. A system for predicting laser damage performance of a surface of an optical element, comprising:

the standard optical element selecting module is used for selecting a standard optical element;

the defect density acquisition module is used for acquiring the absorption defect distribution characteristics of the standard optical element to obtain defect densities with different absorption levels;

the damage performance acquisition module is used for acquiring damage performance; the damage performance comprises a damage threshold and a damage density;

the standard curve establishing module is used for determining the defect density with the highest correlation with the damage performance in the defect densities of different absorption levels of the standard optical element by adopting a Spearman correlation analysis method to obtain the defect density corresponding to each damage performance, and establishing a correlation curve between the damage performance and the defect density corresponding to the damage performance to be used as a standard curve;

and the damage performance determining module is used for acquiring the defect density of the optical element to be detected and determining the damage performance of the optical element to be detected according to the standard curve.

7. The system for predicting laser damage performance of optical element surface as claimed in claim 6, wherein said damage performance obtaining module comprises:

the laser radiation unit is used for radiating the standard optical element by adopting laser with different grades until the standard optical element is damaged;

a damage threshold test unit for testing a damage threshold of the standard optical element;

a damage density acquisition unit, configured to detect a distribution of damage points in the damage area, and acquire a damage density;

and the damage performance acquisition unit is used for acquiring the damage performance of the standard optical element according to the damage threshold and the damage density.

8. The system for predicting laser damage performance of an optical element surface as claimed in claim 6, wherein said defect density obtaining module comprises:

and the photo-thermal common-path interference unit is used for testing the photo-thermal weak absorption coefficient of the standard optical element by adopting a photo-thermal common-path interference technology, acquiring the absorption defect distribution characteristic of the standard optical element and obtaining the defect densities of different absorption levels.

Technical Field

The invention relates to the technical field of optical element surface laser damage assessment, in particular to a method and a system for predicting optical element surface laser damage performance.

Background

A large number of high-performance optical elements such as fused quartz, K9, UBK7, silicon wafers, KDP crystals and other optical elements are used in a large-scale high-power laser device, and along with the continuous improvement of the output energy of the laser device, the problem of laser damage of the optical elements becomes more and more prominent, and the high-performance optical elements become an important bottleneck for limiting the continuous improvement of the output energy of laser.

At present, the actual laser damage performance of most optical elements is far lower than the theoretical value, which indicates that the surface defects remained after the optical elements are processed are important causes of laser damage. The general process of laser damage to the surface of an optical element is as follows: 1) the defect absorbs laser energy, so that the laser energy is transferred to the material and locally reaches a plasma state; 2) the plasma continuously absorbs the laser energy to form local high temperature and high pressure; 3) the host material finally forms surface damage to the local energy deposition response through forms of thermal diffusion, explosive shock waves and the like. It can be seen that the absorption of laser energy by defects as an initial stage of laser damage is a critical step in the development of laser damage. Therefore, the research on the incidence relation between the distribution rule of the absorptive defects on the surface of the optical element and the laser damage performance has important significance for deeply understanding the damage mechanism and establishing an accurate and reliable nondestructive evaluation method for the laser damage performance of the optical element.

Research shows that the defects inducing laser damage of the optical element under the current laser flux mainly include chemical pollution of processing residues and micro-nano physical structure defects, and pollutants are usually embedded in the physical structure defects. The damage performance of the defect part is far lower than that of a defect-free area when the laser irradiates the optical element, so that the characterization of the surface defect of the optical element and the large-caliber statistics thereof are effective and have great significance for evaluating the damage performance of the optical element.

Absorption is a common characteristic parameter of various defects under laser irradiation, and can be used for statistical research of surface defects of laser optical elements. The optical element used under the high-power laser condition has high quality requirement, the residual absorption on the surface is mostly in the ppm order, and the traditional grating spectrometer-based transmittance spectrum cannot obtain reliable data at the low absorption level.

Disclosure of Invention

The invention aims to provide a method and a system for predicting the laser damage performance of the surface of an optical element, which can improve the evaluation accuracy of the damage performance of the optical element on the basis of not damaging the optical element.

In order to achieve the purpose, the invention provides the following scheme:

a method for predicting laser damage performance of an optical element surface, comprising:

selecting a standard optical element;

acquiring the distribution characteristics of the absorption defects of the standard optical element to obtain defect densities with different absorption levels;

obtaining damage performance; the damage performance comprises a damage threshold and a damage density;

determining the defect density with the highest correlation with the damage performance in the defect densities of different absorption levels of the standard optical element by adopting a Spearman correlation analysis method to obtain the defect density corresponding to each damage performance, and establishing a correlation curve between the damage performance and the corresponding defect density as a standard curve;

and acquiring the defect density of the optical element to be detected, and determining the damage performance of the optical element to be detected according to the standard curve.

Optionally, the surface treatment process of the standard optical element is the same as the surface treatment process of the optical element to be measured.

Optionally, the obtaining the impairment performance comprises:

irradiating the standard optical element by adopting laser with different grades until the standard optical element is damaged;

testing the standard optical element for a damage threshold;

detecting the distribution condition of the damage points in the damage area to obtain the damage density;

and acquiring the damage performance of the standard optical element according to the damage threshold and the damage density.

Optionally, a photo-thermal common-path interference technology is adopted to test the photo-thermal weak absorption coefficient of the standard optical element, so as to obtain the absorption defect distribution characteristics of the standard optical element and obtain the defect densities of different absorption levels.

Optionally, a plurality of the standard optical elements are used to obtain the standard curve.

A system for predicting laser damage performance of an optical element surface, comprising:

the standard optical element selecting module is used for selecting a standard optical element;

the defect density acquisition module is used for acquiring the absorption defect distribution characteristics of the standard optical element to obtain defect densities with different absorption levels;

the damage performance acquisition module is used for acquiring damage performance; the damage performance comprises a damage threshold and a damage density;

the standard curve establishing module is used for determining the defect density with the highest correlation with the damage performance in the defect densities of different absorption levels of the standard optical element by adopting a Spearman correlation analysis method to obtain the defect density corresponding to each damage performance, and establishing a correlation curve between the damage performance and the defect density corresponding to the damage performance to be used as a standard curve;

and the damage performance determining module is used for acquiring the defect density of the optical element to be detected and determining the damage performance of the optical element to be detected according to the standard curve.

Optionally, the impairment performance obtaining module includes:

the laser radiation unit is used for radiating the standard optical element by adopting laser with different grades until the standard optical element is damaged;

a damage threshold test unit for testing a damage threshold of the standard optical element;

a damage density acquisition unit, configured to detect a distribution of damage points in the damage area, and acquire a damage density;

and the damage performance acquisition unit is used for acquiring the damage performance of the standard optical element according to the damage threshold and the damage density.

Optionally, the defect density obtaining module includes:

and the photo-thermal common-path interference unit is used for testing the photo-thermal weak absorption coefficient of the standard optical element by adopting a photo-thermal common-path interference technology, acquiring the absorption defect distribution characteristic of the standard optical element and obtaining the defect densities of different absorption levels.

According to the specific embodiment provided by the invention, the invention discloses the following technical effects: according to the method and the system for predicting the laser damage performance of the surface of the optical element, the standard curve corresponding to the defect density and the damage performance of the optical element is constructed by selecting the standard optical element, and the damage performance of the optical element to be measured can be correspondingly obtained by detecting the defect density of the optical element to be measured according to the obtained standard curve, so that the evaluation accuracy of the damage performance of the optical element can be improved on the basis of not damaging the optical element.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

FIG. 1 is a flowchart of a method for predicting laser damage performance of a surface of an optical device according to an embodiment of the present invention;

FIG. 2 is a distribution diagram of test areas on a standard optical element in an embodiment of the present invention;

FIG. 3 is a graph illustrating the distribution of surface absorption defects of a fused silica component in accordance with an embodiment of the present invention;

FIG. 4 is a graph showing the quantitative relationship between the zero probability damage threshold and the defect density of a fused silica device according to an embodiment of the present invention;

FIG. 5 shows a fused silica component 8J/cm in an embodiment of the invention²A quantitative relationship graph of damage density and defect density of (a);

fig. 6 is a schematic structural diagram of a system for predicting laser damage performance of an optical element surface according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention aims to provide a method and a system for predicting the laser damage performance of the surface of an optical element, which can improve the evaluation accuracy of the damage performance of the optical element on the basis of not damaging the optical element.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.

Fig. 1 is a flowchart of a method for predicting laser damage performance of a surface of an optical element according to an embodiment of the present invention, and as shown in fig. 1, a method for predicting laser damage performance of a surface of an optical element includes:

s100, selecting a standard optical element.

S101, acquiring the distribution characteristics of the absorption defects of the standard optical element to obtain defect densities with different absorption levels.

And S102, obtaining the damage performance. The damage performance includes a damage threshold and a damage density.

S103, determining the defect density with the highest correlation with the damage performance in the defect densities of the standard optical element with different absorption levels by using a Spearman correlation analysis method to obtain the defect density corresponding to each damage performance, and establishing a correlation curve between the damage performance and the corresponding defect density as a standard curve.

S104, acquiring the defect density of the optical element to be detected, and determining the damage performance of the optical element to be detected according to the standard curve.

In order to further improve the detection accuracy, the surface treatment process of the adopted standard optical element may be the same as the surface treatment process of the optical element to be detected.

The method has the advantages of non-contact, high sensitivity, high stability, no damage and the like, and can be widely applied to weak absorption detection of thin films and optical materials. Most importantly, the PCI adopts a two-dimensional scanning mode, so that the high-efficiency statistics of the absorptive defects with different calibers of the optical element can be realized, which is difficult to realize by the existing other surface defect detection technologies. Therefore, before S101, the method may further include:

and testing the photo-thermal weak absorption coefficient of the standard optical element by adopting a photo-thermal common path interference technology to obtain the absorption defect distribution characteristic of the standard optical element and obtain the defect densities of different absorption levels, thereby improving the efficiency of obtaining the defect densities of different absorption levels.

In the process of establishing the standard curve, a plurality of standard optical elements similar to the surface treatment process of the optical element to be detected are selected, the surface photothermal absorption of the standard optical elements is detected in a multi-sample, multi-position and two-dimensional scanning mode, the statistical distribution rule of the surface absorption defects of the standard optical elements is analyzed, the standard curve with higher accuracy is established, and the accuracy of the whole detection process is improved.

When obtaining the damage threshold, a low-energy laser is used as the initial energy, and then a certain energy (which may be 1J/cm)²) The steps continuously increase the laser energy, and each energy is irradiated for 1 time until damage occurs. Selecting multiple regions to test the damage probability under different energies by the same laser radiation mode, and then passing the test flux (unit is J/cm)²) And obtaining a damage threshold value according to the damage probability curve. The lesion density at the target flux was obtained using a Raster-scan (sweep scan) approach.

In the testing process, different photo-thermal absorption pumping wavelengths and different pumping powers are selected to test the standard element according to different service conditions of the optical element. And the damage performance test laser wavelength is the same as the absorption defect statistical test wavelength.

The invention isThe optical elements aimed at are fused quartz (fine polishing), K9 glass, UBK7, silicon wafer, KDP and CaF₂Crystals, etc.

The method for predicting the laser damage performance of the surface of the optical element provided by the invention is further described in detail below by taking a fused silica element as an example.

1) Selecting a plurality of standard optical elements similar to the surface treatment process of the optical element to be detected, detecting the surface photothermal absorption of the standard optical elements by adopting a multi-sample, multi-position and two-dimensional scanning mode, and analyzing the statistical distribution rule of the surface absorption defects of the standard optical elements. The method specifically comprises the following steps:

according to the sampling mode shown in fig. 2, each standard sample is tested with PCI in n areas of 3mm × 3mm (n is greater than or equal to 1, the specific value depends on the size and surface quality of the optical element, taking 50mm × 50mm fused quartz as an example, the surface n of higher processing quality is approximately equal to 3), defect distribution densities of different absorption levels under different test calibers are counted by using Matlab, defect distribution density maps of different test calibers are drawn, the minimum sampling area capable of representing the distribution characteristics of large-caliber defects is determined, and an absorption defect distribution density function is fitted. And repeating the steps to test the surface photothermal absorption of a plurality of standard optical elements, and obtaining the absorption defect distribution characteristics of all the standard elements. The resulting distribution curve of surface absorption defects of the fused silica component is shown in fig. 3.

2) And testing the surface laser damage performance of all the standard optical elements in the step 1) according to a standard damage testing process. An R on 1 mode is adopted, namely, a low-energy laser is used as initial energy, then laser energy is continuously increased by a certain energy step, each energy is irradiated for 1 time until damage occurs, and then a damage threshold value is obtained through a test flux and damage probability curve. And obtaining the damage density at the target flux by adopting a Raster-scan (sweep scanning) mode, wherein the sampling area of each fused quartz element is 9cm multiplied by 9 cm.

In the testing process, different photo-thermal absorption pumping wavelengths and different pumping powers are selected according to different application and service conditions of the fused quartz element. And in the testing process, the laser wavelength of the damage performance testing needs to be the same as the pumping wavelength of the absorption defect statistical testing. For a fused quartz element, surface photothermal absorption test pump laser is quasi-continuous light, detection laser is continuous laser, the wavelength of pump laser is 355nm, the power is 1W, the wavelength of detection laser is 632nm, and the power is 5 mW. The laser for the damage performance test is pulse laser with the wavelength of 355nm and the pulse width of 9.3ns, the spot size of the surface irradiated on the sample is phi 2mm, and the modulation degree is lower than 1.6.

3) According to the statistical distribution characteristics of the absorption defects of the standard sample and the corresponding damage performance, analyzing the correlation between the defect density of different absorption grades and the damage performance by a Spearman correlation method, screening the defect density with the highest correlation with the damage performance, and establishing a correlation curve between the defect density and the damage performance (damage threshold and damage density).

4) And (4) carrying out surface photo-thermal absorption test on the optical element to be tested to obtain a defect density distribution rule, obtaining high-correlation absorption grade defect density, and calculating the surface damage threshold and the damage density of the optical element to be tested according to the relation curve diagram obtained in the step (3).

Wherein the Spearman correlation of the zero probability damage threshold of the fused silica component with the defect densities of different absorption levels and 8J/cm thereof²Spearman's correlation of damage density to defect density at different absorption levels is shown in tables 1 and 2 below.

And the quantitative relation between the zero probability damage threshold value and the defect density and 8J/cm²The quantitative relationship of the damage density to the defect density of (a) is shown in fig. 4 and 5, respectively.

Table 1: spireman correlation of zero probability damage threshold and defect density of different absorption levels

Table 2: 8J/cm²Spireman correlation of damage density with defect density at different absorption levels

Wherein Spearman Corr is the Spearman correlation coefficient and Sig is significance.

The damage threshold in this example includes a zero probability damage threshold and a 100% probability damage threshold.

In this example, the surface absorption defect detection and damage performance test of the optical element were performed in a hundred-grade clean environment.

Based on the above, the method for predicting the laser damage performance of the surface of the optical element provided by the invention has the advantages that:

counting the surface absorption defect of a standard element with a surface treatment process similar to that of the optical element to be measured through a multi-sample, multi-position and two-dimensional absorption test to obtain the distribution rule of the surface absorption defect of the standard optical element; meanwhile, laser with the same wavelength as the absorption test wavelength is adopted to carry out standard optical element damage performance to obtain a damage threshold value and damage density; analyzing the correlation between the defect density of different absorption levels and the damage performance according to the statistical distribution characteristics of the absorption defects of the standard element and the corresponding damage performance of the standard element, screening out the absorption level defect with the highest correlation with the damage performance, and establishing a correlation curve between the defect density of the optical element and the damage performance (damage threshold and damage density); the damage threshold value and the damage density are calculated according to the defect density-damage performance relation curve by detecting the surface absorption defect density of the optical element to be detected, so that the nondestructive evaluation of the damage performance of the optical element is realized.

In addition, the present invention provides a system for predicting laser damage performance of an optical element surface, as shown in fig. 6, the system comprising: the device comprises a standard optical element selection module 1, a defect density acquisition module 2, a damage performance acquisition module 3, a standard curve establishment module 4 and a damage performance determination module 5.

The standard optical element selection module 1 is used for selecting a standard optical element;

the defect density acquisition module 2 is used for acquiring the absorption defect distribution characteristics of the standard optical element to obtain defect densities with different absorption levels;

the damage performance acquisition module 3 is used for acquiring damage performance; the damage performance comprises a damage threshold and a damage density;

the standard curve establishing module 4 is configured to determine, by using a Spearman correlation analysis method, a defect density having a highest correlation with the damage performance among the defect densities of the different absorption levels of the standard optical element, to obtain a defect density corresponding to each damage performance, and establish a correlation curve between the damage performance and the defect density corresponding thereto as a standard curve;

the damage performance determining module 5 is configured to obtain a defect density of the optical element to be detected, and determine the damage performance of the optical element to be detected according to the standard curve.

In order to further improve the accuracy of detection, the impairment performance obtaining module 3 may include: the device comprises a laser radiation unit, a damage threshold value testing unit, a damage density obtaining unit and a damage performance obtaining unit.

The laser radiation unit is used for radiating the standard optical element by adopting laser with different grades until the standard optical element is damaged.

The damage threshold test unit is used for testing the damage threshold of the standard optical element.

And the damage density acquisition unit is used for detecting the distribution condition of the damage points in the damage area to acquire the damage density.

And the damage performance acquisition unit is used for acquiring the damage performance of the standard optical element according to the damage threshold and the damage density.

The defect density acquisition module 2 further includes: the method is used for testing the weak absorption coefficient of the surface of the standard optical element by adopting a photo-thermal common-path interference technology, obtaining the absorption defect distribution characteristic of the standard optical element and obtaining the photo-thermal common-path interference unit with different absorption levels of defect density.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.

The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.