Crystal defect nondestructive detection method and system based on pump-probe transient absorption spectrum

Abstract

The present application relates to the technical field of crystal nondestructive testing, and particularly relates to a crystal defect nondestructive testing method and system based on pumped probe transient absorption spectrum, which comprises the following steps: detecting a target region of a crystal to be tested by using pump light and probe light; collecting a transient absorption image of the target region according to a preset time delay between the pump light and the probe light, and extracting a target risk region; focusing the pump light and the probe light, and performing point-by-point scanning on the target risk region by using the focused pump light and probe light; collecting three-dimensional transient absorption intensity distribution and defect dynamic evolution data of each scanning point in the target risk region under different time delays; performing correlation calibration based on the transient absorption image and the three-dimensional transient absorption intensity distribution to obtain defect parameters; and constructing a damage prediction model based on sample damage threshold data, and outputting damage threshold prediction results according to the defect parameters. The purpose is to realize nondestructive and rapid detection of internal defects of deuterated potassium dihydrogen phosphate crystals.

Description

Technical Field

[0001] This invention relates to the field of crystal nondestructive testing technology, specifically to a method and system for nondestructive testing of crystal defects based on pump-probe transient absorption spectroscopy. Background Technology

[0002] Potassium dihydrogen phosphate deuteride (DKDP) crystal is a key optical material used for frequency conversion in high-power laser systems. Intrinsic point defects and impurity defects within the crystal evolve into damage precursors under strong laser irradiation, inducing local energy deposition through linear or nonlinear absorption mechanisms, ultimately leading to irreversible damage. Therefore, accurately characterizing the concentration, type, and spatial distribution of defects within the crystal is crucial for assessing its resistance to laser damage. Currently, the standard methods for evaluating the laser damage resistance of DKDP crystals mainly employ R-on-1 or S-on-1 damage testing, directly irradiating the sample with a high-energy laser until damage occurs. To find alternatives, the industry has developed various detection technologies, including semiconductor defect detection methods based on carrier excitation, material analysis techniques relying on spectral ellipsometric measurements, detection methods based on magnetic response photonic crystal sensors, and defect observation methods using laser scattering imaging.

[0003] Among these methods, carrier-excitation-based detection is suitable for semiconductor materials, but it struggles to effectively detect internal defects in wide-bandgap, highly insulating crystals like potassium deuterated phosphate (KDP). Spectral ellipsometry primarily analyzes the dielectric constant and polarization state changes of materials, failing to acquire transient defect state information closely related to laser damage, and its system complexity hinders rapid detection. Magnetic-response photonic crystal sensors are only applicable to ferromagnetic materials, while KDP, as a non-magnetic optical crystal, cannot be detected through magnetic field response. Laser scattering imaging methods, although capable of observing scattering particles in large crystals, struggle to distinguish defect types and assess the impact of defects on the laser damage threshold. Therefore, existing technologies are insufficient for non-destructive, rapid detection of internal defects in KDP crystals, and even more so for predicting laser damage performance based on defect information. This has become a key bottleneck restricting the improvement of output energy in high-power laser systems. Summary of the Invention

[0004] To achieve non-destructive and rapid detection of internal defects in potassium dihydrogen phosphate crystals, this invention provides a non-destructive detection method and system for crystal defects based on pump-probe transient absorption spectroscopy. The specific technical solution adopted is as follows:

[0005] The first aspect of the present invention provides a non-destructive testing method for crystal defects based on pump-probe transient absorption spectroscopy, the method comprising:

[0006] The target area of ​​the crystal under test is detected using pump light and probe light;

[0007] Based on the preset time delay between the pump light and the probe light, the transient absorption image of the target area under the preset time delay is acquired, and the target risk area of ​​the crystal under test is extracted.

[0008] The pump light and probe light are focused, and the focused pump light and probe light are used to scan the target risk area point by point;

[0009] Collect three-dimensional transient absorption intensity distribution and defect dynamics evolution data of each scanning point in the target risk area under different time delays;

[0010] Based on the correlation calibration of transient absorption images and three-dimensional transient absorption intensity distribution, the defect parameters of the crystal under test are obtained.

[0011] A damage prediction model is constructed based on the sample damage threshold data, and the damage threshold prediction result is output according to the defect parameters of the crystal under test.

[0012] Furthermore, the target area of ​​the crystal under test is probed using pump light and probe light, including:

[0013] By using a femtosecond laser to output a fundamental frequency light wave, a nonlinear frequency conversion is performed on the fundamental frequency light wave to obtain a first wavelength beam as a pump light and a second wavelength beam as a probe light.

[0014] The pump light and probe light are homogenized and expanded respectively to obtain a uniform illumination spot covering the target area.

[0015] Furthermore, based on a preset time delay between the pump light and the probe light, a transient absorption image of the target region under the preset time delay is acquired, including:

[0016] An optical delay device is used to adjust the optical path of the probe light to be greater than that of the pump light, so that the probe light arrives at the target area after a preset time delay relative to the pump light.

[0017] The pump light is periodically modulated by a chopper, so that the pump light intermittently excites the crystal under test at a preset frequency.

[0018] Transmission signals of the probe light are acquired using a photoelectric converter under both pump light excitation and non-excitation states. The transient absorption changes caused by pumping are extracted differentially to obtain the transient absorption image of the target region.

[0019] Furthermore, the target risk region of the crystal under test is extracted, including:

[0020] The power density of the pump light and probe light is adjusted by attenuating the filter to make it lower than the laser-induced damage threshold of the crystal under test.

[0021] The crystal under test is controlled to move in a plane perpendicular to the optical axis with a first preset step size. Transient absorption images are acquired at each moving position, and the transient absorption intensity distribution map of the target depth plane is obtained by stitching the images together.

[0022] The crystal under test is controlled to move along the optical axis at a second preset step size, and the images are repeatedly acquired and stitched at different depth positions. A three-dimensional transient absorption spectrum scanning image of the crystal under test is constructed based on the image matrix.

[0023] Based on the transient absorption intensity in the three-dimensional transient absorption spectrum scan image, pixel regions exceeding a preset intensity threshold are identified as first-level abnormal regions;

[0024] Morphological clustering analysis is performed on the first-level anomaly area to identify spatially continuous clusters with an area greater than a preset area threshold as target risk areas, and the boundary coordinates of the target risk areas are recorded.

[0025] Furthermore, the pump light and probe light are focused, and the focused pump light and probe light are used to scan the target risk area point by point, including:

[0026] The pump light and probe light are focused into collinear spots according to a preset diameter and then illuminated on the target risk area.

[0027] The phase and attenuation information of the probe light transmission signal before and after excitation by the pump light modulated by the chopper are extracted by connecting the lock-in amplifier to the chopper.

[0028] The crystal under test is controlled to move within the target risk area in a third step, so that the focused pump light and probe light can scan the target risk area point by point.

[0029] Furthermore, three-dimensional transient absorption intensity distribution and defect dynamics evolution data of each scanning point in the target risk area under different time delays were collected, including:

[0030] At each scanning point in the target risk area, the relative optical path between the pump light and the probe light is continuously changed by an optical delay device to scan the time delay between the pump light and the probe light.

[0031] Record the evolution curves of transient absorption signals at each scanning point as a function of time delay;

[0032] The crystal under test is controlled to move along the optical axis at a fourth step length, and the transient absorption signal of each scanning point is repeatedly acquired at different depth positions.

[0033] Based on the spatial coordinates of each scanning point and the corresponding time delay, three-dimensional transient absorption intensity distribution and defect dynamics evolution data of the target risk area are constructed.

[0034] Furthermore, based on the transient absorption image and the three-dimensional transient absorption intensity distribution, correlation calibration is performed to obtain the defect parameters of the crystal under test, including:

[0035] Spatial registration is performed between the full-field transient absorption image acquired under a preset time delay and the three-dimensional transient absorption intensity distribution of the target risk area obtained by point-by-point scanning;

[0036] Based on the registration results, an empirical calibration relationship between the global transient absorption intensity and the local defect concentration is established.

[0037] Based on the empirical calibration relationship, the transient absorption image of the crystal under test is converted into defect concentration distribution parameters over the entire crystal domain.

[0038] Furthermore, a damage prediction model is constructed based on sample damage threshold data, including:

[0039] Obtain multiple standard samples with known laser-induced damage thresholds, and the defect parameters of each standard sample;

[0040] A correlation model between the defect parameters of a standard sample and the laser-induced damage threshold is constructed. The correlation model is then trained and validated to obtain a damage prediction model.

[0041] Furthermore, based on the defect parameters of the crystal under test, the damage threshold prediction results are output, including:

[0042] By inputting the defect parameters of the crystal under test into the damage prediction model, the predicted damage threshold values ​​of the entire crystal under test and each target risk area are obtained.

[0043] The predicted damage threshold is compared with the preset acceptance standard. When the predicted damage threshold is higher than the first threshold, a qualified judgment is output. When the predicted damage threshold is between the first threshold and the second threshold, a downgrade judgment is output. When the predicted damage threshold is lower than the second threshold, a unqualified judgment is output.

[0044] The second aspect of the present invention provides a crystal defect nondestructive testing system based on pump-probe transient absorption spectroscopy, used to execute the crystal defect nondestructive testing method based on pump-probe transient absorption spectroscopy described in the first aspect of the present invention, the system comprising:

[0045] The detection module is configured to use pump light and probe light to detect the target area of ​​the crystal under test;

[0046] The risk region extraction module is configured to acquire transient absorption images of the target region under a preset time delay based on the preset time delay between the pump light and the probe light, and extract the target risk region of the crystal under test.

[0047] The focusing scanning module is configured to focus the pump light and the probe light, and use the focused pump light and probe light to scan the target risk area point by point;

[0048] The data acquisition module is configured to collect three-dimensional transient absorption intensity distribution and defect dynamics evolution data of each scanning point in the target risk area under different time delays;

[0049] The correlation calibration module is configured to perform correlation calibration based on transient absorption images and three-dimensional transient absorption intensity distribution to obtain the defect parameters of the crystal under test.

[0050] The prediction output module is configured to build a damage prediction model based on sample damage threshold data and output damage threshold prediction results according to the defect parameters of the crystal under test.

[0051] The present invention has the following beneficial effects:

[0052] This invention provides a non-destructive testing method for crystal defects based on pump-probe transient absorption spectroscopy. This method combines pump-probe transient absorption spectroscopy with a hybrid imaging strategy, offering a non-destructive testing approach for potassium dihydrogen phosphate deuterated crystals. First, the method uses pump and probe light to acquire transient absorption images of the target area at a preset time delay. Image analysis extracts defect-rich target risk areas, enabling rapid screening and accurate location of crystal defects. Then, the identified risk areas are scanned point-by-point with focused focus to obtain the three-dimensional transient absorption intensity distribution and defect dynamics evolution data at each scan point under different time delays. This achieves high-resolution and accurate analysis of key areas while maintaining detection efficiency. Based on this, the transient absorption images obtained from large-scale screening are correlated and calibrated with the three-dimensional data obtained from local fine scanning to obtain defect parameters reflecting the overall defect state of the crystal. A prediction model is then constructed based on sample damage threshold data, ultimately outputting the crystal's damage threshold prediction result. This technical solution directly detects damage precursors directly related to laser damage, and the acquired defect parameters are intrinsically correlated with the crystal's damage resistance, thus achieving highly accurate prediction of crystal damage thresholds under non-destructive conditions. Meanwhile, by employing a strategy of screening and positioning before focusing and analyzing, the detection efficiency and information depth are effectively balanced, solving the problem of balancing detection area and spatial resolution in the detection of large-size optical components. Attached Figure Description

[0053] The above and other objects, features, and advantages of the present invention will become more apparent from the more detailed description of the embodiments of the invention in conjunction with the accompanying drawings. The drawings are provided to further illustrate the embodiments of the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings, the same reference numerals generally represent the same parts or steps.

[0054] Figure 1 This is a schematic flowchart of a non-destructive testing method for crystal defects based on pump-probe transient absorption spectroscopy provided in an exemplary embodiment of the present invention;

[0055] Figure 2 This is a schematic diagram of a wide-field imaging nondestructive testing optical path provided by an exemplary embodiment of the present invention;

[0056] Figure 3 This is a schematic diagram of a point-by-point scanning non-destructive testing optical path provided by an exemplary embodiment of the present invention;

[0057] Figure 4 This is a three-dimensional schematic diagram of a crystal point defect enrichment region provided in an exemplary embodiment of the present invention;

[0058] Figure 5 This is a schematic diagram of a crystal defect nondestructive testing system based on pump-probe transient absorption spectroscopy provided by an exemplary embodiment of the present invention. Detailed Implementation

[0059] The present invention will be further described below with reference to the embodiments shown in the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments of the present invention. It should be understood that the present invention is not limited to the exemplary embodiments described herein.

[0060] It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention.

[0061] Those skilled in the art will understand that the terms "first," "second," etc., in the embodiments of the present invention are only used to distinguish different steps, devices, or modules, and do not represent any specific technical meaning, nor do they indicate a necessary logical order between them.

[0062] It should also be understood that in the embodiments of the present invention, "multiple" can refer to two or more, and "at least one" can refer to one, two or more.

[0063] It should also be understood that any component, data or structure mentioned in the embodiments of the present invention can generally be understood as one or more unless explicitly defined or given contrary instructions in the context.

[0064] Furthermore, the term "and / or" in this invention is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this invention generally indicates that the preceding and following related objects have an "or" relationship.

[0065] It should also be understood that the description of the various embodiments in this invention emphasizes the differences between the various embodiments, and the similarities or similarities can be referred to each other. For the sake of brevity, they will not be described in detail.

[0066] At the same time, it should be understood that, for ease of description, the dimensions of the various parts shown in the accompanying drawings are not drawn according to actual scale.

[0067] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use.

[0068] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0069] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0070] Technical Concept: KDP / DKDP crystals exhibit transient optical absorption under ultraviolet laser irradiation. This phenomenon originates from the capture of electron-hole pairs generated by ultraviolet photon excitation by lattice defects, forming free radicals such as A radicals, B radicals, and H radicals. 0 / D 0 The crystal contains isocenters, which exhibit characteristic absorption bands in the visible light band. The relaxation dynamics of transient absorption are controlled by inter-defect tunneling recombination and thermal diffusion processes, and its attenuation law is closely related to the defect concentration and type. Therefore, by measuring the transient absorption signal, key information about internal defects in the crystal can be inferred. Based on this, transient absorption spectroscopy is applied to the non-destructive testing of DKDP crystals. A safe ultraviolet pulsed laser beam, below the damage threshold, is used as the pump source to controllably induce transient defects in the crystal. Simultaneously, a visible light beam is used as the probe light to highly sensitively detect the characteristic absorption of the defects and its changes over time. By analyzing the acquired transient absorption signal, the core defect parameters that determine the crystal's resistance to laser damage are inferred. By accurately determining the delay times of the probe and pump lights, the transient absorption intensity at the defect location is captured, thereby determining the presence of a defect at that location and realizing a shift from passive destructive testing to active non-destructive diagnosis and prediction.

[0071] Example 1

[0072] Figure 1 This is a schematic flowchart of a non-destructive testing method for crystal defects based on pump-probe transient absorption spectroscopy provided by an exemplary embodiment of the present invention.

[0073] Specifically, refer to Figure 1 The non-destructive testing method for crystal defects based on pump-probe transient absorption spectroscopy includes:

[0074] Step 100: The target area of ​​the crystal under test is probed using pump light and probe light; specifically, in this embodiment, potassium dihydrogen phosphate crystal (DKDP) is used as the crystal under test, and a structure is built as follows... Figure 2 The wide-field imaging non-destructive testing optical path shown in the figure fixes the crystal under test on a three-dimensional displacement stage, uses a femtosecond laser to output the fundamental frequency light wave, and generates pump light and probe light respectively through nonlinear frequency conversion.

[0075] Preferably, the pump light is a 257 nm ultraviolet pulsed laser, whose photon energy is sufficient to excite intrinsic point defects and impurity defects inside the crystal, causing these defects to enter transient defect states with characteristic light absorption within a short time. The probe light is a 515 nm visible light, which is located in the transparent window of the crystal and can sensitively detect the characteristic absorption of the transient defect states without causing additional excitation. Both the pump light and the probe light are beam-expanded by a homogenization and beam-expanding system to form a uniform illumination spot covering the target area of ​​the crystal under test.

[0076] Step 200: Based on the preset time delay between the pump light and the probe light, acquire the transient absorption image of the target area under the preset time delay, and extract the target risk area of ​​the crystal under test; specifically, adjust the optical path of the probe light to be greater than that of the pump light by means of an optical delay device, so that the probe light arrives at the target area after a preset time delay relative to the pump light.

[0077] After pump light excitation, defects form within approximately 2 picoseconds, at which point the transient defect state exhibits the most significant absorption of the probe light. Therefore, the preset time delay is preferably set to 3 picoseconds to capture the transient absorption signal with the maximum intensity. During acquisition, the pump light is periodically modulated using a chopper, causing it to intermittently excite the crystal under test at a preset frequency. A photoelectric converter is used to acquire the transmission signal of the probe light in both pump-excited and unexcited states. The transient absorption change caused by the pump light is extracted differentially to obtain a transient absorption image of the target region. The transient absorption intensity of each pixel in this image reflects the point defect concentration at the corresponding location. Furthermore, an attenuator is used to adjust the power density of the pump light and probe light, ensuring it is well below the laser-induced damage threshold of the crystal under test, guaranteeing no damage to the crystal during the detection process. The crystal under test is controlled to move in a plane perpendicular to the optical axis with a first preset step size. A transient absorption image is acquired at each moving position, and the transient absorption intensity distribution map of the target depth plane is obtained by image stitching. The crystal under test is controlled to move along the optical axis at a second preset step size, and images are repeatedly acquired and stitched together at different depth positions to construct a three-dimensional transient absorption spectrum scan image of the crystal under test based on the image matrix. Pixel regions exceeding a preset intensity threshold are identified as primary anomalous regions based on the transient absorption intensity in the three-dimensional transient absorption spectrum scan image. Morphological clustering analysis is performed on the primary anomalous regions, and spatially continuous clusters with an area greater than a preset area threshold are identified as target risk regions.

[0078] Step 300: Focus the pump light and probe light, and use the focused pump light and probe light to scan the target risk area point by point; for details, see Figure 3 As shown, by removing Figure 2 The homogenization and beam-expanding system in the pump and probe optical paths switches the pump and probe beams into collinear small spots focused on the target risk region. The spot diameter can be set to the micrometer scale according to the detection accuracy requirements. A lock-in amplifier connected to a chopper extracts the phase and attenuation information of the probe beam transmission signal before and after excitation by the chopper-modulated pump beam, further improving the signal-to-noise ratio and detection sensitivity. The crystal under test is controlled to move within the target risk region in a third-step manner, allowing the focused pump and probe beams to scan the target risk region point by point.

[0079] Step 400: Collect three-dimensional transient absorption intensity distribution and defect dynamics evolution data at each scanning point in the target risk area under different time delays. Specifically, at each scanning point in the target risk area, the relative optical path between the pump light and the probe light is continuously changed by an optical delay device to scan the time delay between the pump light and the probe light. Record the evolution curve of the transient absorption signal at each scanning point as a function of time delay. This curve reveals the dynamics of the entire process of defect generation, evolution, and annihilation. Control the crystal under test to move along the optical axis with a fourth step length, and repeatedly collect the transient absorption signal at each scanning point at different depth positions. Based on the spatial coordinates of each scanning point and the corresponding time delay, construct three-dimensional transient absorption intensity distribution and defect dynamics evolution data of the target risk area to achieve a complete spatiotemporal characterization of defects in the key area.

[0080] Step 500: Based on the transient absorption image and the three-dimensional transient absorption intensity distribution, correlation calibration is performed to obtain the defect parameters of the crystal under test. Specifically, the full-field transient absorption image acquired under a preset time delay is spatially registered with the three-dimensional transient absorption intensity distribution of the target risk area obtained through point-by-point scanning to establish a consistent correspondence of spatial coordinates. Based on the registration result, an empirical calibration relationship between the full-field transient absorption intensity and the local defect concentration is established. According to this empirical calibration relationship, the full-field transient absorption image of the crystal under test is converted into defect concentration distribution parameters of the entire crystal domain, thereby realizing the conversion from image grayscale information to quantitative physical parameters.

[0081] Step 600: Construct a damage prediction model based on sample damage threshold data, and output the damage threshold prediction result according to the defect parameters of the crystal under test. Specifically, collect multiple standard samples with known laser-induced damage thresholds, and obtain the defect parameters of each standard sample using the same method as for the crystal under test. Construct a correlation model between the defect parameters of the standard samples and the laser-induced damage threshold, and train and validate the correlation model using machine learning or statistical regression methods to obtain the damage prediction model. Input the defect parameters of the crystal under test into the damage prediction model to obtain the predicted damage threshold values ​​for the entire crystal under test and each target risk area. Compare the predicted damage threshold values ​​with the preset acceptance criteria. When the predicted damage threshold value is higher than the first threshold, output a pass / fail judgment; when the predicted damage threshold value is between the first and second thresholds, output a downgrade judgment; when the predicted damage threshold value is lower than the second threshold, output a fail / unacceptable judgment.

[0082] In summary, the non-destructive testing method for crystal defects based on pump-probe transient absorption spectroscopy provided in this embodiment first rapidly screens the entire crystal and automatically identifies target risk areas using a wide-field imaging mode. Then, a point-scanning mode is used to perform high-resolution point-by-point scanning of the risk areas to acquire three-dimensional transient absorption intensity distribution and defect dynamics evolution data. After correlating and calibrating the data from both stages, the global defect parameters of the crystal are obtained, and a damage threshold prediction result is output based on a damage prediction model. This method directly detects damage precursors directly related to laser damage, and the acquired defect parameters are intrinsically correlated with the crystal's damage resistance, thus achieving highly accurate prediction of crystal damage thresholds under non-destructive conditions. Furthermore, the strategy of screening and locating first, followed by focused analysis, balances detection efficiency and information depth, solving the problem of balancing detection area and spatial resolution in the detection of large-size optical components.

[0083] Example 2

[0084] Based on the above embodiment 1, as an optional implementation method, see [link to embodiment 1]. Figure 2 and Figure 4 As shown, the target area of ​​the crystal under test is probed using pump light and probe light, including:

[0085] Step 110: Use a femtosecond laser to output a fundamental frequency light wave, and perform nonlinear frequency conversion on the fundamental frequency light wave to obtain a first wavelength beam as pump light and a second wavelength beam as probe light.

[0086] Specifically, in this embodiment, a femtosecond laser is used as the light source. The laser outputs a fundamental frequency light with a wavelength of 1030 nm, a pulse width of 20 femtoseconds, a repetition frequency of 1 kHz, and a single pulse energy of 5 millijoules. The fundamental frequency light output by the laser first undergoes nonlinear frequency conversion through a first nonlinear optical crystal (LBO) to generate a second-harmonic light with a wavelength of 515 nm. This second-harmonic light serves as the probe light, with a frequency doubling efficiency of approximately 30%. The fundamental frequency light and the second-harmonic light are separated by a harmonic beam splitter, and the remaining fundamental frequency light is filtered out. The separated second-harmonic light then undergoes second-frequency doubling through a second nonlinear optical crystal (CLBO) to obtain a fourth-harmonic light with a wavelength of 257 nm. This fourth-harmonic light serves as the pump light, with a second-frequency doubling efficiency of approximately 20%. The pulse width of the fourth-harmonic light after passing through the crystal is less than 150 femtoseconds. Through the above two-stage frequency doubling process, pump light with a wavelength in the ultraviolet band and probe light with a wavelength in the visible band are obtained. The photon energy of the pump light is sufficient to excite the intrinsic point defects and impurity defects inside the crystal under test, causing them to enter the transient defect state with characteristic light absorption. The wavelength of the probe light is located in the transparent window of the crystal, which can sensitively detect the characteristic absorption of the transient defect state without causing additional excitation.

[0087] Step 120: The pump light and probe light are homogenized and expanded to obtain uniform illumination spots covering the target area. Specifically, the pump light and probe light, obtained after nonlinear frequency conversion, are collimated by lenses into spots with a diameter of 100 micrometers. Subsequently, the pump light and probe light are split by a harmonic beam splitter and enter independent homogenization and beam expansion systems. The homogenization and beam expansion system adopts a structure combining a microlens array and a beam expander. The microlens array is used to spatially divide and reintegrate the incident beam, eliminating the non-uniformity of beam intensity distribution, and the beam expander is used to expand the beam diameter to the required size. After homogenization and beam expansion, the pump light and probe light each form illumination spots with a diameter of 1 cm and uniform intensity distribution. The two spots overlap spatially, covering the same target area of ​​the crystal under test. This uniform large-spot illumination method allows the transient absorption information of all pixels in the target area to be acquired in a single exposure.

[0088] In summary, this embodiment utilizes a femtosecond laser combined with two-stage nonlinear frequency conversion to generate ultraviolet pump light suitable for defect excitation and visible probe light suitable for transient absorption detection. A homogenization and beam expansion system is then employed to shape both beams, resulting in a large, uniformly illuminated spot covering the target area. This achieves optimized control over the selection of the light source wavelength and the spot quality, ensuring high-sensitivity, high-uniformity transient absorption imaging. Furthermore, by precisely controlling the power density of both the pump and probe lights to remain below the crystal's damage threshold, the detection process is ensured to be completely non-destructive.

[0089] Example 3

[0090] Based on Embodiments 1 and 2 above, as an optional implementation, according to a preset time delay between the pump light and the probe light, a transient absorption image of the target region under the preset time delay is acquired, and the target risk region of the crystal under test is extracted, including:

[0091] Step 210: Use an optical delay device to adjust the optical path of the probe light to be greater than that of the pump light, so that the probe light arrives at the target area after a preset delay relative to the pump light.

[0092] Specifically, the optical retarder employs a computer-controlled electrically operated displacement platform, and its delay structure consists of two mirrors. After the pump and probe beams are split, the probe beam enters the delay path and is reflected by the mirror assembly to extend the optical path, thereby achieving a time delay relative to the pump beam. By electrically and precisely translating the horizontal position of the two mirrors, the optical path of the probe beam can be continuously changed, thus precisely adjusting the delay time. Since the point defects inside the crystal form transient defect states within approximately 2 picoseconds after pump excitation, the absorption of the probe beam is most significant at this time. Therefore, the delay time of the probe beam relative to the pump beam is preset to 3 picoseconds. According to the relationship between the speed of light and the optical path, achieving a 3 picosecond delay requires the optical path of the probe beam to be approximately 0.9 mm longer than that of the pump beam. This optical path difference is precisely controlled by the optical retarder to ensure that the probe beam reaches the target region when the defect state concentration reaches its peak.

[0093] Step 220: Periodically modulate the pump light using a chopper to intermittently excite the crystal under test at a preset frequency. Specifically, a chopper connected to a lock-in amplifier is inserted into the optical path of the pump light. The chopper rotates at a fixed frequency at high speed, periodically blocking the passing pump light, thereby achieving intermittent excitation of the crystal. In this embodiment, the chopper frequency is set to 500 Hz, meaning the pump light alternately switches between on and off states at a frequency of 500 Hz. When the pump light passes through the chopper, the crystal is excited to generate a transient defect state; when the pump light is blocked, the crystal is in an unexcited state.

[0094] Step 230: Using a photoelectric converter, the transmission signal of the probe light is acquired under both pump light excitation and non-excitation states. The transient absorption change caused by the pump is extracted differentially to obtain a transient absorption image of the target region. Specifically, in this embodiment, a CCD camera is preferably used as the photoelectric converter, with a frame rate set to 3000 frames per second for high-speed image capture. Under the synchronous control of the chopper, the CCD camera acquires the transmission image of the probe light under both pump light on and off states. When the pump light is on, the crystal is excited, and the probe light intensity attenuates due to absorption by transient defect states as it passes through the excited region. When the pump light is off, the probe light passes through the unexcited region, and the transmission intensity is the background value. By performing differential processing on the images under the two states, background interference can be eliminated, and the transient absorption change caused solely by the pump light can be extracted, thereby obtaining a transient absorption image of the target region at a preset time delay. This image directly reflects the distribution of defects inside the crystal at that moment.

[0095] Step 240: Adjust the power density of the pump light and probe light using attenuators to ensure they are below the laser-induced damage threshold of the crystal under test. Specifically, adjustable attenuators are installed in the optical paths of the pump light and probe light, respectively. By adjusting the attenuation of the attenuators, the power density of the light reaching the crystal is controlled. In this embodiment, the power density of the pump light is adjusted to approximately 1 gigawatt per square centimeter, and the power density of the probe light is adjusted to approximately 0.01 gigawatts per square centimeter. Both are far below the damage threshold of the potassium dihydrogen phosphate crystal, thus ensuring that the entire detection process does not damage the crystal.

[0096] Step 250: Control the crystal under test to move in a plane perpendicular to the optical axis with a first preset step size. Acquire transient absorption images at each moving position, and obtain a transient absorption intensity distribution map of the target depth plane by image stitching. Specifically, fix the crystal under test on a high-precision three-dimensional displacement stage, and control the displacement stage to move in two dimensions in a plane perpendicular to the optical axis with a step size of 5 mm. At each stopping position, acquire the transient absorption image at that position according to the method described in steps 210 to 230. After acquisition, the host computer software performs flat-field correction on the images at each position to eliminate the influence of uneven illumination, and stitches the images according to the movement sequence of the displacement stage to generate a large-area transient absorption intensity distribution map of the current depth plane, that is, a survey distribution map of the defect concentration at the initial point of the crystal.

[0097] Step 260: Control the crystal under test to move along the optical axis with a second preset step size, repeatedly collect and stitch images at different depth positions, and construct a three-dimensional transient absorption spectrum scanning image of the crystal under test based on the image matrix;

[0098] Specifically, after acquiring data at one depth plane, the displacement stage is moved along the optical axis in a second step of 2 mm to the next depth position. Step 250 is repeated to acquire the transient absorption intensity distribution map of that depth plane. This process is repeated layer by layer until the entire crystal thickness is covered. The images from each depth plane are then filled into a three-dimensional image matrix according to their spatial coordinates, ultimately constructing a three-dimensional transient absorption spectrum scan image of the crystal under test. This enables the detection of the three-dimensional distribution of defects from the crystal surface to different depths within the crystal.

[0099] Step 270: Based on the transient absorption intensity in the three-dimensional transient absorption spectrum scan image, identify pixel regions exceeding a preset intensity threshold as primary anomaly regions. Specifically, in the obtained three-dimensional transient absorption image, the transient absorption intensity is represented by color scales; the higher the intensity value of a pixel, the higher the defect concentration at that location. A preset intensity threshold is set, and all pixel regions in the image whose transient absorption intensity exceeds this threshold are marked as primary anomaly regions. These regions initially indicate possible defect enrichment locations.

[0100] Step 280: Perform morphological clustering analysis on the primary anomaly areas. Clusters that are spatially continuous and have an area greater than a preset area threshold are identified as target risk regions, and the boundary coordinates of these target risk regions are recorded. Specifically, morphological clustering analysis is performed on the marked primary anomaly areas to merge spatially adjacent or continuous pixels into clusters, and the area of ​​each cluster is calculated. A preset area threshold is set, such as 0.01 square millimeters. Clusters with an area greater than this threshold are identified as target risk regions, i.e., point defect enrichment areas that cause laser damage. The three-dimensional boundary coordinates of each target risk region are recorded as the positioning basis for subsequent high-resolution fine scanning.

[0101] In summary, this embodiment precisely controls the time delay between the pump light and the probe light using an optical delay device, achieves periodic modulation and differential detection using a chopper and lock-in amplifier, and obtains high signal-to-noise ratio transient absorption images by combining high-speed acquisition with a CCD camera. Through step scanning and image stitching techniques, a three-dimensional transient absorption spectrum image of the crystal is constructed, enabling the detection of the three-dimensional distribution of defects from the surface to the interior. Furthermore, through threshold recognition and morphological clustering analysis, target risk regions rich in defects are automatically extracted and their boundary coordinates are recorded. This technical solution provides a reliable means for the rapid screening and precise location of defects in large-area crystals, and identifies key areas for subsequent high-resolution fine scanning.

[0102] Example 4

[0103] Based on the above embodiments 1, 2, and 3, see [link to embodiment 1]. Figure 3 As shown, as an optional implementation, the pump light and probe light are focused, and the focused pump light and probe light are used to scan the target risk area point by point, including:

[0104] Step 310: Focus the pump light and probe light into collinear spots according to the preset diameter and illuminate the target risk area. Specifically, after completing the full-field rapid imaging screening of the crystal and obtaining the boundary coordinates of the target risk area, remove the homogenization and beam expansion systems in the pump light and probe light paths, switching the beams from wide-field illumination mode to point scanning mode. Adjust the pump light and probe light into strictly collinear beams through a focusing lens group and focus them into a small spot with a diameter of approximately 100 micrometers, forming a tiny probe voxel on the sample. The focused pump light and probe light act together on the same tiny region of the crystal. The pump light excites point defects within the voxel to form transient defect states, and the probe light then passes through the region and is absorbed, providing a signal source for subsequent high-sensitivity detection.

[0105] Step 320: Connect the lock-in amplifier to the chopper to extract the phase and attenuation information of the probe light transmission signal before and after pump light excitation modulated by the chopper. Specifically, connect the chopper to the lock-in amplifier. The chopper periodically modulates the pump light at a fixed frequency, and the lock-in amplifier is connected to the single-point detector in the probe light path. Using the chopper's modulation frequency as a reference, the lock-in amplifier extracts the weak transient absorption signal component with the same frequency as the pump light excitation from the detector's output signal, while effectively suppressing background noise and interference. Through the processing of the lock-in amplifier, the phase change and attenuation amplitude information of the probe light transmission signal before and after pump light excitation can be obtained, thereby achieving high-sensitivity, high-signal-to-noise ratio detection of the transient absorption signal.

[0106] Step 330: Control the crystal under test to move within the target risk area at a third step length, allowing the focused pump light and probe light to scan the target risk area point by point. Specifically, the host computer control system reads the three-dimensional boundary coordinates of each target risk area identified earlier and controls the high-precision three-dimensional displacement stage to move the crystal under test to the starting scanning position of the first risk area. Within the risk area, a step scan is performed in a plane perpendicular to the optical axis at a third step length of 20 micrometers. Simultaneously, the transient absorption signal at each scanning point is acquired using the methods described in steps 310 and 320. After completing the scan of one depth plane, the crystal is moved to the next depth along the optical axis at a fourth step length, and the scan continues until the entire three-dimensional space of the risk area is covered. At this point, the CCD camera is replaced with a single-point detector, continuously recording the intensity change of the probe light transmission signal at each scanning point, and storing the spatial coordinates of each scanning point in correspondence with the corresponding transient absorption signal intensity. Finally, through data processing, a three-dimensional transient absorption image with sub-micrometer spatial resolution is formed, accurately presenting the microscopic distribution of defects within the target risk area.

[0107] In summary, this embodiment achieves high spatial resolution three-dimensional imaging and quantitative analysis of defect-rich areas by focusing and scanning the screened target risk areas point by point. By employing collinear focusing spots to form tiny probe voxels, combined with the high-sensitivity detection of a lock-in amplifier, the transient absorption intensity and dynamic information of defects within each voxel can be acquired, thereby obtaining a detailed defect distribution within the risk area. This technical solution, while ensuring detection efficiency, concentrates high-precision analytical resources on key areas, effectively revealing the microstructure and distribution characteristics of defects.

[0108] Example 5

[0109] Based on the above embodiments 1, 2, 3, and 4, as an optional implementation method, three-dimensional transient absorption intensity distribution and defect dynamics evolution data of each scanning point in the target risk area under different time delays are collected, including:

[0110] Step 410: At each scanning point in the target risk area, the relative optical path between the pump light and the probe light is continuously changed using an optical retarder to scan the time delay between them. Specifically, at each scanning point within the target risk area, the electric displacement platform of the optical retarder is controlled by a computer to continuously change the optical path between the probe light and the pump light at set step intervals, thereby accurately scanning the time delay between the pump light and the probe light. The scanning range of the time delay covers the femtosecond to nanosecond scale to comprehensively obtain the complete dynamic process of transient defect states from generation to annihilation. At each time delay point, the pump light excites the crystal to generate a transient defect state, and the probe light then passes through the excited region, its transmission intensity attenuating due to the characteristic absorption of the defect state.

[0111] Step 420: Record the evolution curve of the transient absorption signal at each scanning point as a function of time delay. Specifically, at each scanning point, for each set time delay, the difference in the transmission intensity of the probe light under pump light and pump-free conditions is measured using a single-point detector. This difference is the transient absorption signal intensity. Arranging the transient absorption signal intensities corresponding to each time delay in chronological order yields the evolution curve of the transient absorption signal at that scanning point as a function of time delay. This curve quantitatively describes the entire process of the generation, evolution, and annihilation of the transient defect state after the defect at that location is excited. Curve characteristics such as peak intensity and decay time constant reflect the concentration and type of the defect.

[0112] Step 430: Control the crystal under test to move along the optical axis by a fourth step, and repeatedly collect transient absorption signals at each scanning point at different depth positions. Specifically, after completing the acquisition of transient absorption signals at all scanning points in the current depth plane, the host computer controls the high-precision three-dimensional displacement stage to move the crystal under test to the next depth position by a fourth step along the optical axis. At the new depth position, repeat the operations of steps 410 and 420, and perform time-delay scanning again on each scanning point in the same target risk area and record the evolution curve. Scan layer by layer in this way until the entire range of the target risk area in the depth direction is covered, thereby obtaining transient absorption dynamics data of the risk area at different depths.

[0113] Step 440: Based on the spatial coordinates of each scanning point and the corresponding time delay, construct the three-dimensional transient absorption intensity distribution and defect dynamics evolution data of the target risk area. Specifically, associate the three-dimensional spatial coordinates of each scanning point with its transient absorption signal intensity at different time delays to construct a four-dimensional dataset containing spatial and temporal dimensions. Based on this dataset, a three-dimensional transient absorption intensity distribution image of the target risk area at any specified time delay can be generated, intuitively displaying the spatial distribution of defects; simultaneously, the transient absorption evolution curve of any spatial location point can be extracted to analyze its defect dynamics characteristics. The host computer system processes the raw data collected by the detector through an algorithm, filling each pixel into the three-dimensional image matrix according to the movement sequence of the displacement stage, ultimately forming a three-dimensional transient absorption spectrum image with sub-micron spatial resolution and femtosecond temporal resolution, i.e., a fine three-dimensional distribution and dynamic behavior spectrum of point defects inside the crystal.

[0114] In summary, this embodiment acquires the evolution curve of the transient absorption signal over time by performing time-delayed scanning at each scanning point within the target risk area. Combined with three-dimensional spatial step scanning, a four-dimensional dataset containing three spatial dimensions and one temporal dimension is constructed. This technical solution not only reveals the spatial distribution of defects within the crystal but also provides complete dynamic information on defect generation, evolution, and annihilation. It provides crucial data for a deeper understanding of the microscopic mechanisms of defects and for establishing a quantitative correlation between defect parameters and laser damage thresholds, thereby improving the accuracy and reliability of predicting the laser damage resistance of crystals.

[0115] Example 6

[0116] Based on the above embodiments 1, 2, 3, 4, and 5, as an optional implementation, a correlation calibration is performed based on the transient absorption image and the three-dimensional transient absorption intensity distribution to obtain the defect parameters of the crystal under test, including:

[0117] Step 510: Spatially register the full-field transient absorption image acquired under a preset time delay with the three-dimensional transient absorption intensity distribution of the target risk area obtained through point-by-point scanning. Specifically, import the crystal full-field three-dimensional transient absorption spectrum scan image obtained in Example 3 and the high-resolution three-dimensional transient absorption intensity distribution image of the target risk area obtained in Example 5 into the data processing system. Using the boundary coordinates of the target risk area as a reference, an image registration algorithm is used to spatially align the two sets of image data to ensure that the risk area position in the full-field image and the corresponding area in the high-resolution scan image are accurately matched in spatial coordinates. During the spatial registration process, the image resolution difference is considered, and interpolation and coordinate transformation are used to achieve pixel-level correspondence between the two sets of data in the same spatial coordinate system.

[0118] Step 520: Based on the registration results, establish an empirical calibration relationship between the overall transient absorption intensity and the local defect concentration. Specifically, within the target risk area where spatial registration has been completed, extract the transient absorption intensity values ​​at each location point in the overall transient absorption image, and simultaneously extract the three-dimensional transient absorption intensity distribution data obtained from high-resolution scanning at the corresponding locations. Since high-resolution scanning data has higher spatial resolution and quantitative accuracy, it can be considered a true reflection of the defect concentration at that location. Using the overall transient absorption intensity as the independent variable and the defect concentration parameter obtained from high-resolution scanning as the dependent variable, data fitting is performed on all corresponding pixels within the risk area to establish an empirical calibration relationship between the two. This calibration relationship can be a linear relationship or a nonlinear function. Its mathematical expression and correlation coefficient are determined through regression analysis, thereby converting the relative absorption intensity of the overall image into a physically meaningful absolute defect concentration.

[0119] Step 530: Based on the empirical calibration relationship, the transient absorption image of the crystal under test is converted into a global defect concentration distribution parameter. Specifically, the empirical calibration relationship established in step 520 is applied to the full-field three-dimensional transient absorption spectrum scan image of the crystal under test. Each pixel in the image is converted and calculated, mapping the original transient absorption intensity value to the corresponding defect concentration value. The converted image data is the global defect concentration three-dimensional distribution parameter, where the value of each pixel quantitatively represents the point defect concentration at that location. This defect concentration distribution parameter not only includes the full-field information obtained through rapid screening but also ensures quantitative accuracy through fine calibration of the risk area, providing reliable input data for subsequent damage threshold prediction.

[0120] In summary, this embodiment spatially registers and quantitatively calibrates the full-field rapid screening images with local high-resolution scanning data, establishing an empirical calibration relationship between the full-field transient absorption intensity and the local defect concentration. Based on this, the transient absorption images of the entire crystal are converted into quantitatively significant defect concentration distribution parameters. Ultimately, this achieves a combination of rapid screening efficiency and high-resolution quantitative accuracy, preserving the comprehensiveness of large-area detection while ensuring data accuracy through local calibration.

[0121] Example 7

[0122] Based on the above embodiments 1, 2, 3, 4, 5, and 6, as an optional implementation, a damage prediction model is constructed based on sample damage threshold data, and the damage threshold prediction result is output according to the defect parameters of the crystal under test, including:

[0123] Step 610: Obtain multiple standard samples with known laser-induced damage thresholds and the defect parameters of each standard sample. Specifically, a batch of representative potassium dihydrogen phosphate deuteride crystal samples are selected as standard samples. The laser-induced damage thresholds of these samples have been accurately determined using traditional R-on-1 or S-on-1 damage testing methods. The damage threshold data covers a wide range from low to high to reflect the damage resistance performance of crystals of different quality grades. For each standard sample, the same testing procedure as the crystal to be tested is adopted, i.e., according to the methods described in Examples 1 to 6, first, a full-field rapid imaging screening is performed to obtain its three-dimensional transient absorption image; then, a high-resolution point-by-point scan is performed on the identified target risk area to obtain the three-dimensional transient absorption intensity distribution; finally, the global defect concentration distribution parameters of the standard sample are obtained through correlation calibration. This establishes a defect parameter dataset containing multiple standard samples and their corresponding laser-induced damage threshold dataset.

[0124] Step 620: Construct a correlation model between the defect parameters of the standard sample and the laser-induced damage threshold. Train and validate the correlation model to obtain a damage prediction model. Specifically, use the defect parameters of the standard sample as input features and the corresponding laser-induced damage threshold as the output target. Use machine learning or statistical regression methods to construct the correlation model. The model input features may include the global average defect concentration, the peak defect concentration in the risk area, defect spatial distribution characteristic parameters, and defect dynamic characteristic parameters such as decay time constant. Divide the standard sample dataset into a training set and a validation set. Use the training set to train the model, and use an optimization algorithm to determine the model parameters so that the model can accurately fit the relationship between the defect parameters and the damage threshold. Then use the validation set to validate the trained model and evaluate its prediction accuracy and generalization ability. After multiple iterations of optimization, a damage prediction model with satisfactory prediction performance is obtained.

[0125] Step 630: Input the defect parameters of the crystal under test into the damage prediction model to obtain the predicted damage threshold values ​​for the entire crystal under test and each target risk region. Specifically, for the crystal under test, the global defect concentration distribution parameters have been obtained in Example 6. Input these defect parameters into the damage prediction model constructed in Step 620. The model calculates the predicted laser-induced damage threshold value of the crystal under test based on the input feature parameters. At the same time, for each target risk region identified in the crystal under test, the defect feature parameters of that region can be extracted and input into the model separately to obtain the predicted local damage threshold value for each risk region. These predicted values ​​quantitatively reflect the laser damage resistance of the crystal under test and its key regions.

[0126] Step 640: Compare the predicted damage threshold value with the preset acceptance criteria. If the predicted damage threshold value is higher than the first threshold, output a pass / fail judgment. If the predicted damage threshold value is between the first and second thresholds, output a downgraded use judgment. If the predicted damage threshold value is lower than the second threshold, output a fail / unacceptable judgment. Specifically, based on the actual application requirements of optical components in high-power laser systems, two acceptance thresholds are preset: the first threshold is the pass / fail standard, indicating that the crystal can be safely used in the highest energy density conditions; the second threshold is the downgraded use standard, indicating that the crystal is only suitable for lower energy density conditions. Compare the global damage threshold prediction value of the crystal under test with these two thresholds. If the predicted value is higher than the first threshold, the crystal is determined to be a pass / fail product and can be directly used in the design-required conditions; if the predicted value is between the first and second thresholds, it is determined to be downgraded and recommended for use in lower energy density applications; if the predicted value is lower than the second threshold, it is determined to be unacceptable, indicating that the crystal has a high risk of laser damage and is not suitable for use in high-power laser systems. Furthermore, based on the predicted local damage threshold values ​​of each target risk area, further optimization suggestions can be given, such as avoiding the target risk area by cutting to improve the availability of the crystal.

[0127] In summary, this embodiment achieves a leap from non-destructive testing results to quantitative prediction of damage performance by establishing a correlation model between the defect parameters of standard samples and the laser-induced damage threshold. By inputting the defect parameters of the crystal under test into the model, its predicted damage threshold value can be quickly obtained, and the quality judgment result can be output in conjunction with preset acceptance criteria, providing a direct and reliable decision-making basis for the engineering application of crystals.

[0128] Example 8

[0129] It should be understood that the crystal defect nondestructive testing method based on pump-probe transient absorption spectroscopy described in the foregoing embodiments herein can also be similarly applied to the following crystal defect nondestructive testing system based on pump-probe transient absorption spectroscopy for similar extension. For simplicity, it is not described in detail.

[0130] Figure 5 This is an exemplary embodiment of the present invention, providing a non-destructive testing system for crystal defects based on pump-probe transient absorption spectroscopy. (Refer to...) Figure 5 The system includes:

[0131] The detection module is configured to use pump light and probe light to detect the target area of ​​the crystal under test;

[0132] The risk region extraction module is configured to acquire transient absorption images of the target region under a preset time delay based on the preset time delay between the pump light and the probe light, and extract the target risk region of the crystal under test.

[0133] The focusing scanning module is configured to focus the pump light and the probe light, and use the focused pump light and probe light to scan the target risk area point by point;

[0134] The data acquisition module is configured to collect three-dimensional transient absorption intensity distribution and defect dynamics evolution data of each scanning point in the target risk area under different time delays;

[0135] The correlation calibration module is configured to perform correlation calibration based on transient absorption images and three-dimensional transient absorption intensity distribution to obtain the defect parameters of the crystal under test.

[0136] The prediction output module is configured to build a damage prediction model based on sample damage threshold data and output damage threshold prediction results according to the defect parameters of the crystal under test.

[0137] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details of the invention described above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the specific details described above.

[0138] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For system embodiments, since they largely correspond to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0139] The block diagrams of devices, apparatuses, devices, and systems involved in this invention are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, apparatuses, devices, and systems can be connected, arranged, and configured in any manner. Words such as “comprising,” “including,” “having,” etc., are open-ended terms meaning “including but not limited to,” and are used interchangeably with them. The terms “or” and “and” as used herein refer to the terms “and / or,” and are used interchangeably with them unless the context clearly indicates otherwise. The term “such as” as used herein refers to the phrase “such as but not limited to,” and is used interchangeably with it.

[0140] The methods and apparatus of the present invention may be implemented in many ways. For example, they may be implemented by software, hardware, firmware, or any combination of software, hardware, and firmware. The above-described order of steps for the methods is for illustrative purposes only, and the steps of the methods of the present invention are not limited to the order specifically described above unless otherwise specifically stated. Furthermore, in some embodiments, the present invention may also be implemented as a program recorded on a recording medium, the program comprising machine-readable instructions for implementing the methods according to the present invention. Thus, the present invention also covers recording media storing programs for performing the methods according to the present invention.

[0141] It should also be noted that in the apparatus, device, and method of the present invention, the components or steps can be disassembled and / or recombined. These disassemblies and / or recombinations should be considered as equivalent solutions of the present invention.

[0142] The above description of aspects of the invention is provided to enable any person skilled in the art to make or use the invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of the invention. Therefore, the invention is not intended to be limited to the aspects shown herein, but rather to be carried out within the widest scope consistent with the principles and novel features of the invention herein.

[0143] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of the invention to the forms described herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations therein.

[0144] It should be noted that the order of the above embodiments of the present invention is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. The processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0145] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

Claims

1. A non-destructive testing method for crystal defects based on pump-probe transient absorption spectroscopy, characterized in that, The method includes: The target area of ​​the crystal under test is detected using pump light and probe light; Based on a preset time delay between the pump light and the probe light, a transient absorption image of the target region is acquired under the preset time delay, and the target risk region of the crystal under test is extracted, including: The power density of the pump light and probe light is adjusted by attenuating the filter to make it lower than the laser-induced damage threshold of the crystal under test. The crystal under test is controlled to move in a plane perpendicular to the optical axis with a first preset step size. Transient absorption images are acquired at each moving position, and the transient absorption intensity distribution map of the target depth plane is obtained by stitching the images together. The crystal under test is controlled to move along the optical axis at a second preset step size, and the images are repeatedly acquired and stitched at different depth positions. A three-dimensional transient absorption spectrum scanning image of the crystal under test is constructed based on the image matrix. Based on the transient absorption intensity in the three-dimensional transient absorption spectrum scan image, pixel regions exceeding a preset intensity threshold are identified as first-level abnormal regions; Morphological clustering analysis is performed on the first-level anomaly area to identify spatially continuous clusters with an area greater than a preset area threshold as target risk areas, and the boundary coordinates of the target risk areas are recorded. The pump light and probe light are focused, and the focused pump light and probe light are used to scan the target risk area point by point; Collect three-dimensional transient absorption intensity distribution and defect dynamics evolution data of each scanning point in the target risk area under different time delays; Based on the correlation calibration of transient absorption images and three-dimensional transient absorption intensity distribution, the defect parameters of the crystal under test are obtained. A damage prediction model is constructed based on the sample damage threshold data, and the damage threshold prediction result is output according to the defect parameters of the crystal under test.

2. The non-destructive testing method for crystal defects based on pump-probe transient absorption spectroscopy as described in claim 1, characterized in that, The target region of the crystal under test is probed using pump light and probe light, including: By using a femtosecond laser to output a fundamental frequency light wave, a nonlinear frequency conversion is performed on the fundamental frequency light wave to obtain a first wavelength beam as a pump light and a second wavelength beam as a probe light. The pump light and probe light are homogenized and expanded respectively to obtain a uniform illumination spot covering the target area.

3. The non-destructive testing method for crystal defects based on pump-probe transient absorption spectroscopy as described in claim 1, characterized in that, Based on a preset time delay between the pump light and the probe light, a transient absorption image of the target region is acquired under the preset time delay, including: An optical delay device is used to adjust the optical path of the probe light to be greater than that of the pump light, so that the probe light arrives at the target area after a preset time delay relative to the pump light. The pump light is periodically modulated by a chopper, so that the pump light intermittently excites the crystal under test at a preset frequency. Transmission signals of the probe light are acquired using a photoelectric converter under both pump light excitation and non-excitation states. The transient absorption changes caused by pumping are extracted differentially to obtain a transient absorption image of the target region.

4. The non-destructive testing method for crystal defects based on pump-probe transient absorption spectroscopy as described in claim 1, characterized in that, The pump light and probe light are focused, and the focused pump light and probe light are used to scan the target risk area point by point, including: The pump light and probe light are focused into collinear spots according to a preset diameter and then illuminated on the target risk area. The phase and attenuation information of the probe light transmission signal before and after excitation by the pump light modulated by the chopper are extracted by connecting the lock-in amplifier to the chopper. The crystal under test is controlled to move within the target risk area in a third step, so that the focused pump light and probe light can scan the target risk area point by point.

5. The non-destructive testing method for crystal defects based on pump-probe transient absorption spectroscopy as described in claim 1, characterized in that, The three-dimensional transient absorption intensity distribution and defect dynamics evolution data of each scanning point in the target risk area under different time delays were collected, including: At each scanning point in the target risk area, the relative optical path between the pump light and the probe light is continuously changed by an optical delay device to scan the time delay between the pump light and the probe light. Record the evolution curves of transient absorption signals at each scanning point as a function of time delay; The crystal under test is controlled to move along the optical axis at a fourth step length, and the transient absorption signal of each scanning point is repeatedly acquired at different depth positions. Based on the spatial coordinates of each scanning point and the corresponding time delay, three-dimensional transient absorption intensity distribution and defect dynamics evolution data of the target risk area are constructed.

6. The non-destructive testing method for crystal defects based on pump-probe transient absorption spectroscopy as described in claim 1, characterized in that, Based on the correlation calibration of transient absorption images and three-dimensional transient absorption intensity distribution, the defect parameters of the crystal under test are obtained, including: Spatial registration is performed between the full-field transient absorption image acquired under a preset time delay and the three-dimensional transient absorption intensity distribution of the target risk area obtained by point-by-point scanning; Based on the registration results, an empirical calibration relationship between the global transient absorption intensity and the local defect concentration is established. Based on the empirical calibration relationship, the transient absorption image of the crystal under test is converted into defect concentration distribution parameters over the entire crystal domain.

7. The non-destructive testing method for crystal defects based on pump-probe transient absorption spectroscopy as described in claim 1, characterized in that, A damage prediction model is constructed based on sample damage threshold data, including: Obtain multiple standard samples with known laser-induced damage thresholds, and the defect parameters of each standard sample; A correlation model between the defect parameters of a standard sample and the laser-induced damage threshold is constructed. The correlation model is then trained and validated to obtain a damage prediction model.

8. The non-destructive testing method for crystal defects based on pump-probe transient absorption spectroscopy as described in claim 1, characterized in that, Based on the defect parameters of the crystal under test, the damage threshold prediction results are output, including: By inputting the defect parameters of the crystal under test into the damage prediction model, the predicted damage threshold values ​​of the entire crystal under test and each target risk area are obtained. The predicted damage threshold is compared with the preset acceptance standard. When the predicted damage threshold is higher than the first threshold, a qualified judgment is output. When the predicted damage threshold is between the first threshold and the second threshold, a downgrade judgment is output. When the predicted damage threshold is lower than the second threshold, a unqualified judgment is output.

9. A non-destructive testing system for crystal defects based on pump-probe transient absorption spectroscopy, characterized in that, The system is used to perform the nondestructive testing method for crystal defects based on pump-probe transient absorption spectroscopy as described in any one of claims 1 to 8, the system comprising: The detection module is configured to use pump light and probe light to detect the target area of ​​the crystal under test; The risk region extraction module is configured to acquire transient absorption images of the target region under a preset time delay based on the preset time delay between the pump light and the probe light, and extract the target risk region of the crystal under test. The focusing scanning module is configured to focus the pump light and the probe light, and use the focused pump light and probe light to scan the target risk area point by point; The data acquisition module is configured to collect three-dimensional transient absorption intensity distribution and defect dynamics evolution data of each scanning point in the target risk area under different time delays; The correlation calibration module is configured to perform correlation calibration based on transient absorption images and three-dimensional transient absorption intensity distribution to obtain the defect parameters of the crystal under test. The prediction output module is configured to build a damage prediction model based on sample damage threshold data and output damage threshold prediction results according to the defect parameters of the crystal under test.

Images