An optical performance analysis method based on crystal intrinsic defect concentration characterization

Abstract

This invention discloses an optical performance analysis method based on the characterization of intrinsic defect concentration in crystals, belonging to the field of engineering optics technology. It addresses the lack of existing analytical methods for the impact of intrinsic defects in crystal surface structural defects on the optical performance of components. The method includes the following steps: 1. Determining the elemental composition and distribution of crystal surface structural defects using X-ray energy dispersive spectroscopy; 2. Performing photoluminescence detection on different regions of the crystal surface using photoluminescence methods, and combining the elemental composition and distribution obtained in step 1 to determine the type of intrinsic defect introduced by the crystal surface defects; 3. Establishing a mapping model between fluorescence intensity and defect concentration; 4. Determining the concentration of each type of intrinsic defect under different surface structural defects; 5. Analyzing the evolution of the defect-state crystal structure, electronic structure, and optical absorption performance under different defect concentrations. This invention establishes the correlation between crystal surface structural defects and the crystal's resistance to laser damage.

Description

Technical Field

[0001] This invention belongs to the field of engineering optics technology, and more specifically, relates to an optical performance analysis method based on the characterization of intrinsic defect concentration in crystals. Background Technology

[0002] As a typical large-size, wide-bandgap dielectric material, KDP crystals possess a high theoretical laser-induced damage threshold (LIDT). Due to their large nonlinear coefficient, high transmittance to ultraviolet and infrared lasers, and good optical homogeneity, they are widely used in optoelectronic switches and frequency doubling devices in inertial confinement fusion (ICF) systems. However, due to the inherent softness and brittleness of the crystal material, ultra-precision machining easily introduces numerous micrometer-scale external structural defects onto its surface, as well as a large number of intrinsic structural defects within the crystal. Under intense ultraviolet laser irradiation, these multi-scale defects can significantly reduce the device's resistance to laser damage, causing damage and hindering the output performance of these high-power solid-state laser devices.

[0003] Currently, researchers both domestically and internationally primarily focus on micron-level structural defects on the surfaces of optical components such as crystals during processing. They have investigated the surfaces of optical components and employed various characterization methods to identify and study the defect types and formation mechanisms of KDP crystal fly-cut surfaces. Some reports from both domestic and international sources mention that, based on the structure of residual defects on the crystal surface, they can be classified into four categories: cracks, pits, scratches, and protrusions. Furthermore, the presence of surface defects is a major cause of severe laser damage to crystals. In addition, defects such as surface scratches, subsurface microcracks, and impurities present on the surface of optical components after machining are more likely to induce damage to the optical components under strong laser irradiation.

[0004] It is generally believed that KDP crystals, due to their preparation and processing methods, exhibit not only numerous micrometer-scale structural defects on their surface but also a large number of atomic-scale intrinsic defects. The poor mechanical properties of processed KDP crystals lead to internal fractures, resulting in surface micro-defects such as micro-pits and micro-cracks, accompanied by numerous intrinsic defects. Furthermore, time-resolved photoluminescence spectroscopy can detect a large number of intrinsic defects in KDP crystals, existing in clusters, such as vacancies and interstitials. In addition, the multiphoton absorption caused by the introduced defect energy levels leads to a decrease in the laser-induced damage threshold (LIDT) of the device. The structural defects introduced during the fly-cutting process of KDP crystals are always accompanied by a large number of intrinsic defects, which significantly reduce the crystal's resistance to laser damage. However, the underlying mechanism by which these multi-scale defects, such as intrinsic defects associated with crystal surface structural defects, reduce the device's resistance to laser damage is not well understood. An effective method is lacking to characterize the intrinsic defects associated with crystal surface structural defects and to analyze the influence of defect concentration on the ability to resist laser damage, in order to fundamentally understand the mechanism of laser-induced damage. Summary of the Invention

[0005] The technical problem to be solved by this invention is:

[0006] Existing technologies lack the intrinsic mechanism by which cross-scale defects, such as intrinsic defects accompanying crystal structural defects, reduce the laser damage resistance of components. Therefore, there is a lack of analytical methods for analyzing the impact of intrinsic defects in crystal surface structural defects on the optical performance of components.

[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0008] This invention provides an optical performance analysis method based on the characterization of intrinsic defect concentration in crystals, comprising the following steps:

[0009] Step 1: Prepare typical structural defects present during processing on the crystal surface, and determine the elemental composition and distribution under the structural defects on the crystal surface by X-ray energy dispersive spectroscopy analysis.

[0010] Step 2: Use photoluminescence to detect photoluminescence in different regions of the crystal surface. Combine the elemental composition and distribution obtained in Step 1 to determine the type of intrinsic defects introduced by the crystal surface defects.

[0011] Step 3: Establish a mapping model between fluorescence intensity and defect concentration;

[0012] Step 4: Determine the concentration of each type of intrinsic defect under different surface structure defects;

[0013] Step 5: Using first-principles calculations, analyze the evolution of crystal structure, electronic structure, and optical absorption properties of the crystal defect states under different defect concentrations.

[0014] Furthermore, the typical structural defects described in step one include: pits, transverse cracks, and radial cracks.

[0015] Furthermore, the photoluminescence method described in step two uses excitation light with a wavelength of 430 nm to collect photoluminescence spectra of different regions on the crystal defect surface in the range of 300-800 nm, and performs peak fitting on the spectra to determine the intrinsic defect type introduced by the crystal surface defects.

[0016] Furthermore, the mapping model between fluorescence intensity and defect concentration described in step three is specifically as follows:

[0017] I F =kφI0εlc

[0018] Where I F denoted as fluorescence intensity, φ as fluorescence quantum yield, k as proportionality constant, I0 as incident light intensity, ε as molar extinction coefficient, l as optical path length, and c as sample concentration.

[0019] Furthermore, the method for constructing the mapping relationship model between fluorescence intensity and defect concentration is as follows:

[0020] Based on fluorescence intensity I F Since it is proportional to the fluorescence quantum yield φ and the amount of light absorbed, then:

[0021] I F =φ(I0-I)

[0022] Where I0 is the intensity of the incident light and I is the intensity of the transmitted light.

[0023] According to Beer-Lambert's law, the absorbance A of monochromatic light passing through a homogeneous medium is directly proportional to the concentration c of the sample substance. Therefore:

[0024]

[0025] Where ε is the molar extinction coefficient and l is the optical path length;

[0026] A mapping model between fluorescence intensity and defect concentration was further obtained.

[0027] Furthermore, in step five, first-principles calculations are used to calculate crystals with intrinsic defects. Considering the concentration of intrinsic defects in the crystal, the corresponding number of atoms in the perfect crystal supercell system is deleted to obtain defect supercell systems with different concentrations, and an optical performance calculation model is constructed.

[0028] Based on the first-principles calculation method of density functional theory (DFT), the generalized gradient approximation (GGA) is used to relax the crystal structure to obtain the steady-state crystal structure at different concentrations. Then, the evolution of the electronic structure and optical absorption properties of crystals with different concentrations of intrinsic defects is calculated. During the calculation, the convergence criterion of atomic forces is less than 0.01 eV / A.

[0029] Furthermore, the calculation of the evolution law of optical absorption performance described in step five is based on the Kramers-Koehler relation, which derives the relationship between the dielectric function and optical properties during electronic transitions from the dielectric constant, namely:

[0030]

[0031] Where ε2(ω) is the imaginary part of the dielectric function, reflecting optical absorption properties, e is the electron charge, m is the mass of the free electron, ε0 is the vacuum permittivity, C and V are the conduction band and valence band, respectively, and E C (K), E V (K) represents the eigenlevels in the conduction and valence bands, respectively; BZ is the first Brillouin zone; K is the electron wave vector; a is the vector potential; and M... V,C It is a commutative matrix element, and ω is the angular frequency.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] An optical performance analysis method based on the characterization of intrinsic defect concentration in crystals.

[0034] (1) This invention reveals the influence mechanism of surface structural defects on laser damage of crystals at the atomic level, and finally establishes the correlation between surface structural defects and the laser damage resistance of crystals.

[0035] (2) This invention explores the effects of different concentrations of intrinsic defects on crystal structure, optical properties and electronic structure at the atomic scale, and reveals that controlling intrinsic defects and their content is an effective method to fundamentally improve the laser damage resistance of crystals with surface defects.

[0036] (3) This invention helps to elucidate the influence mechanism of surface processing defects on crystal damage performance under strong light irradiation, and provides theoretical guidance for suppressing surface defects and improving the laser damage resistance of crystal components in ultra-precision processing. Attached Figure Description

[0037] Figure 1 This is a flowchart of the optical performance analysis method based on the intrinsic defect concentration characterization of crystal in an embodiment of the present invention;

[0038] Figure 2 The image shows the surface microstructure of the KDP crystal cut surface and the pre-set defect region in an embodiment of the present invention.

[0039] Figure 3 This is a comparison of the EDS element content of the KDP crystal fly-cut surface and the pre-set defect region in an embodiment of the present invention.

[0040] Figure 4 These are the photoluminescence spectra of the defect-free and transverse crack defect regions on the fly-cut surface of the KDP crystal in this embodiment of the invention.

[0041] Figure 5 The diagram shows the relaxation states of the KDP crystal under different defect concentrations in the embodiments of the present invention.

[0042] Figure 6 The KDP crystal surface in the embodiments of the present invention has different V O Electronic structure diagram at defect concentration;

[0043] Figure 7 Different V in the embodiments of the present invention O Optical absorption properties of KDP crystal at defect concentration. Detailed Implementation

[0044] In the description of this invention, it should be noted that the terms "first," "second," and "third" mentioned in the embodiments of this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," and "third" may explicitly or implicitly include one or more of that feature.

[0045] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0046] like Figure 1 As shown, this invention provides an optical performance analysis method based on the characterization of intrinsic crystal defect concentration, comprising the following steps:

[0047] Step 1: Prepare typical structural defects present during processing on the crystal surface, and analyze the elemental composition and distribution under the structural defects on the crystal surface using X-ray energy dispersive spectroscopy.

[0048] Step 2: Use photoluminescence to detect photoluminescence in different regions of the crystal surface. Combine the elemental composition and distribution obtained in Step 1 to determine the type of intrinsic defects introduced by the crystal surface defects.

[0049] Step 3: Establish a mapping model between fluorescence intensity and defect concentration;

[0050] Step 4: Determine the concentration of each type of intrinsic defect under different surface structure defects;

[0051] Step 5: Using first-principles calculations, analyze the evolution of crystal structure, electronic structure, and optical absorption properties of the crystal defect states under different defect concentrations.

[0052] This invention helps to investigate the influence of intrinsic defects associated with different types of micron-scale structural defects on the optical properties of crystals. Characterizing these intrinsic defects and analyzing their concentration effects facilitates the establishment of a correlation between surface structural defects and the laser damage resistance of crystals. Furthermore, this invention elucidates the mechanism by which surface processing defects affect crystal damage resistance under strong light irradiation at the atomic scale, providing theoretical guidance for suppressing surface defects and improving laser damage resistance during ultra-precision crystal machining.

[0053] For KDP crystals, a typical structural defect present during the flying cut process was prepared on the KDP crystal surface by applying a force of 100g using a Vickers indenter, such as... Figure 2 As shown, the defects include: pits, transverse cracks, and radial cracks.

[0054] Qualitative and semi-quantitative characterization of the elemental composition and distribution beneath surface structural defects in KDP crystals was performed using a scanning electron microscope equipped with an X-ray energy dispersive spectroscopy (EDS) detector. Figure 3 The comparison of EDS elemental content on the cut surface of KDP crystal and the pre-set defect region shown in the figure reveals that, apart from the undetectable H element, only intrinsic K, O, and P elements exist inside the KDP crystal. Moreover, the presence of radial cracks, transverse cracks, and pits on the KDP surface does not introduce other types of impurity ions into the crystal. At the same time, the O element distribution in the transverse crack defect on the crystal surface has significant structural characteristics and exhibits the phenomenon of missing O atoms. However, the O element distribution in the pit region of the crystal surface is more uniform than that in the transverse crack defect and does not show significant missing phenomena.

[0055] Furthermore, the photoluminescence method described in step two uses excitation light with a wavelength of 430 nm to collect photoluminescence spectra of different regions on the crystal defect surface in the range of 300-800 nm, and performs peak fitting on the spectra to determine the intrinsic defect type introduced by the crystal surface defects.

[0056] like Figure 4 The photoluminescence spectra of different defect regions are shown, and Gaussian fitting was performed on the spectra to determine the four Gaussian peaks of AD; Table 1 shows the defect type and structure to which each fitted peak in the photoluminescence spectrum of different defect regions on the fly-cut surface of KDP crystal belongs.

[0057] Table 1

[0058]

[0059] and Figure 4 The A peak obtained from the fitting is caused by hydrogen vacancy defects generated during growth or subsequent processing, the B peak is related to the presence of A radicals and oxygen vacancy defects, and the C and D peaks are attributed to POHC defects. Therefore, the surface defect region introduces an additional D peak compared to the defect-free surface, and the intensity of all four peaks is significantly increased.

[0060] Furthermore, the mapping model between fluorescence intensity and defect concentration described in step three is specifically as follows:

[0061] I F =kφI0εlc

[0062] Where I F denoted as fluorescence intensity, φ as fluorescence quantum yield, k as proportionality constant, I0 as incident light intensity, ε as molar extinction coefficient, l as optical path length, and c as sample concentration.

[0063] Furthermore, the method for constructing the mapping relationship model between fluorescence intensity and defect concentration is as follows:

[0064] Based on fluorescence intensity I F Since it is proportional to the fluorescence quantum yield φ and the amount of light absorbed, then:

[0065] I F =φ(I0-I)

[0066] Where I0 is the intensity of the incident light and I is the intensity of the transmitted light.

[0067] According to Beer-Lambert's law, the absorbance A of monochromatic light passing through a homogeneous (transparent) medium is directly proportional to the concentration c of the sample substance. Therefore:

[0068]

[0069] Where ε is the molar extinction coefficient and l is the optical path length;

[0070] A mapping model between fluorescence intensity and defect concentration was further obtained.

[0071] Furthermore, in step four, based on the constructed mapping model between fluorescence intensity and defect concentration, the concentration of each type of intrinsic defect under different surface structural defects is calculated according to the type of intrinsic defects introduced by crystal surface defects. Among them, the intrinsic defect content is the lowest on the defect-free fly-cut surface. As the intrinsic defect concentration increases with the increase of radial cracks, transverse cracks, and pit defects, it can be determined that structural defects introduced on the crystal surface during processing will generate more intrinsic defects. Among them, the oxygen vacancy defect, which is associated with peak B, has the highest content.

[0072] Furthermore, in step five, first-principles calculations were performed on the KDP crystal with intrinsic defects, constructing a KDP crystal with lattice constants a = b = 7.444 Å and c = 6.967 Å. A 1x2x2 supercell system containing 128 atoms was constructed. Considering the concentration of intrinsic defects in the crystal, the corresponding number of atoms in the perfect KDP crystal supercell system was deleted to obtain defect supercell systems with different concentrations, and an optical performance calculation model was constructed.

[0073] Based on the first-principles calculation method of density functional theory (DFT), the generalized gradient approximation (GGA) is used to relax the crystal structure to obtain the steady-state crystal structure. Then, the electronic structure and optical absorption properties of KDP crystals with different concentrations of intrinsic defects are calculated. During the calculation, the convergence criterion of atomic forces is less than 0.01 eV / A.

[0074] Furthermore, the calculation of the evolution law of optical absorption performance described in step five is based on the Kramers-Koehler relation, which derives the relationship between the dielectric function and optical properties during electronic transitions from the dielectric constant, namely:

[0075]

[0076] Where ε2(ω) is the imaginary part of the dielectric function, reflecting optical absorption properties, e is the electron charge, m is the mass of the free electron, ε0 is the vacuum permittivity, C and V are the conduction band and valence band, respectively, and E C (K), E V (K) represents the eigenlevels in the conduction and valence bands, respectively; BZ is the first Brillouin zone; K is the electron wave vector; a is the vector potential; and M... V,C It is a commutative matrix element, and ω is the angular frequency.

[0077] Analysis of the steady-state crystal structure of crystals with different defect concentrations:

[0078] First, based on different V O (Oxygen vacancy defect) defect concentration in the supercell structure is used for structural relaxation to optimize the model, such as Figure 5 The relaxation states of the KDP crystal structure under different defect concentrations are shown, and it is found to be similar to V. O Two PO4 particles connected by defects 3- The reason for the shortened distance between the P and H atoms in the group is related to V. O Two PO4 particles connected by defects 3- Groups attract each other, causing the distance between two groups to shorten, and the distance between the two groups gradually shortens as the defect concentration increases.

[0079] Analysis of the electronic structure of crystal defect states under different defect concentrations:

[0080] Obtaining such as Figure 6 The electronic structure and total density of states distribution on the surface of the KDP crystal at different concentrations are shown, V O The increase in defect concentration affects the band gap width E of KDP crystal. g There is some impact; as the defect concentration increases, V O The defect level introduced by the defect will gradually shift the conduction band; when V O When the defect concentration increases from 0.787% to 0.820%, the band gap width decreases from 5.974 eV to 5.692 eV. Therefore, the increase in intrinsic defect concentration will gradually affect the electronic structure of the crystal, causing the defect energy level to shift in the band gap, eventually leading to the initiation of damage.

[0081] The optical absorption properties of crystal defect states under different defect concentrations were analyzed.

[0082] To further determine the different V O The effect of defect concentration on the optical properties of crystals was investigated, and the imaginary part of the dielectric function of KDP crystals was studied under different V values. O The optical absorption properties of KDP crystals at defect concentrations are as follows: Figure 7 As shown, when V O When the defect concentration is 0.787%, an additional optical absorption peak is introduced near the absorption edge. At this point, V... O The introduction of defects does not have a destructive effect on the crystal energy level structure; however, as the defect concentration increases, the introduced optical absorption peak gradually exhibits a redshift behavior, making it easier for electrons to undergo transitions.

[0083] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method for analyzing optical performance based on the characterization of intrinsic defect concentration in crystals, characterized in that, Includes the following steps: Step 1: Prepare typical structural defects present during processing on the crystal surface, and determine the elemental composition and distribution under the structural defects on the crystal surface by X-ray energy dispersive spectroscopy analysis. Step 2: Use photoluminescence to detect photoluminescence in different regions of the crystal surface. Combine the elemental composition and distribution obtained in Step 1 to determine the type of intrinsic defects introduced by the crystal surface defects. Step 3: Establish a mapping model between fluorescence intensity and defect concentration; Step 4: Determine the concentration of each type of intrinsic defect under different surface structure defects; Step 5: Using first-principles calculations, analyze the evolution of crystal structure, electronic structure, and optical absorption properties of the crystal defect states under different defect concentrations.

2. The optical performance analysis method based on the intrinsic defect concentration characterization of crystal according to claim 1, characterized in that, The typical structural defects mentioned in step one include: pits, transverse cracks, and radial cracks.

3. The optical performance analysis method based on the intrinsic defect concentration characterization of crystals according to claim 1, characterized in that, The photoluminescence method described in step two uses excitation light with a wavelength of 430 nm to collect photoluminescence spectra of different regions on the surface of crystal defects in the range of 300-800 nm, and performs peak fitting on the spectra to determine the intrinsic defect type introduced by the crystal surface defects.

4. The optical performance analysis method based on the intrinsic defect concentration characterization of crystal according to claim 1, characterized in that, The mapping model between fluorescence intensity and defect concentration described in step three is as follows: I F =kφI0εlc Where I F denoted as fluorescence intensity, φ as fluorescence quantum yield, k as proportionality constant, I0 as incident light intensity, ε as molar extinction coefficient, l as optical path length, and c as sample concentration.

5. The optical performance analysis method based on the intrinsic defect concentration characterization of crystal according to claim 4, characterized in that, The method for constructing the mapping relationship model between fluorescence intensity and defect concentration is as follows: Based on fluorescence intensity I F Since it is proportional to the fluorescence quantum yield φ and the amount of light absorbed, then: AND F =φ(I0-I) Where I0 is the intensity of the incident light, and I is the intensity of the transmitted light; According to Beer-Lambert's law, the absorbance A of monochromatic light passing through a homogeneous medium is directly proportional to the concentration c of the sample substance. Therefore: Where ε is the molar extinction coefficient and l is the optical path length; A mapping model between fluorescence intensity and defect concentration was further obtained.

6. The optical performance analysis method based on the intrinsic defect concentration characterization of crystal according to claim 1, characterized in that, In step five, first-principles calculations are used to calculate crystals with intrinsic defects. Considering the concentration of intrinsic defects in the crystal, the corresponding number of atoms in the perfect crystal supercell system is deleted to obtain defect supercell systems with different concentrations, and an optical performance calculation model is constructed. Based on the first-principles calculation method of density functional theory (DFT), the generalized gradient approximation (GGA) is used to relax the crystal structure to obtain the steady-state crystal structure at different concentrations. Then, the evolution of the electronic structure and optical absorption properties of crystals with different concentrations of intrinsic defects is calculated. During the calculation, the convergence criterion of atomic forces is less than 0.01 eV / A.

7. The optical performance analysis method based on the intrinsic defect concentration characterization of crystal according to claim 6, characterized in that, The calculation of the evolution law of optical absorption performance in step five is based on the Kramers-Koehler relation, which derives the relationship between the dielectric function and optical properties during electronic transitions from the dielectric constant. That is: Where ε2(ω) is the imaginary part of the dielectric function, reflecting optical absorption properties, e is the electron charge, m is the mass of the free electron, ε0 is the vacuum permittivity, C and V are the conduction band and valence band, respectively, and E C (K) and EV(K) represent the eigenlevels in the conduction and valence bands, respectively. BZ is the first Brillouin zone, K is the electron wave vector, a is the vector potential, and M... V,C It is a commutative matrix element, and ω is the angular frequency.

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