Method for obtaining laser damage threshold and photoacoustic measuring device

Abstract

This invention provides a method for obtaining a laser damage threshold, comprising constructing a model for obtaining the laser damage threshold. The model includes an instantaneous damage model and a thermal accumulation damage model. The instantaneous damage model represents the volumetric heat source distribution, electron temperature change, lattice temperature change, and stress transmission after a single-pulse laser irradiates a sample material. The thermal accumulation damage model represents the volumetric heat source distribution, electron temperature change, and lattice temperature change influenced by the environment after multi-pulse laser irradiates the sample material. The method obtains the physical property parameters of the test material and the laser source parameters. Based on the physical property parameters of the test material, the laser source parameters, and the model for obtaining the laser damage threshold, the laser damage threshold is obtained. This method eliminates the time and material cost associated with numerous destructive experiments, reducing costs while improving the detection efficiency of the laser damage threshold. This invention also provides a photoacoustic measurement device.

Description

Technical Field

[0001] This invention relates to the field of laser ultrasonic testing technology, and in particular to a method for obtaining laser damage threshold and a photoacoustic measuring device. Background Technology

[0002] Laser ultrasound technology is a novel non-destructive ultrasonic testing technique that uses a laser source to excite ultrasonic signals within a sample material and then detects them, thereby studying and measuring the propagation of acoustic signals and the physical properties of the sample. Since the pulse width of the laser light source directly determines the frequency and corresponding wavelength of the generated ultrasonic signal, laser ultrasound signals using ultrashort pulse lasers typically operate in the GHz to THz frequency range, giving this technique extremely high spatial resolution, unavailable in traditional ultrasonic testing techniques. Therefore, laser ultrasound measurement technology is widely used in critical stages of semiconductor fabrication processes such as thickness measurement, defect detection, property characterization, and in-situ detection. However, for sample materials with different physical properties, the parameter requirements of the laser source during testing vary, and the corresponding laser damage thresholds often differ significantly. Therefore, accurately determining the laser damage threshold during measurement for different sample materials and laser source parameters is crucial not only for protecting the sample material from damage but also for further improving the measurement signal within a non-destructive range, making it essential for laser ultrasound measurement. Currently, the laser damage threshold for different sample materials is mostly obtained through a large number of destructive experiments. This process is relatively complicated and inefficient. When dealing with new materials for which there are no corresponding empirical parameters, it often requires a lot of time and material costs, which greatly reduces the overall efficiency of the ultrasonic measurement process.

[0003] Therefore, it is necessary to provide a novel method for obtaining the laser damage threshold and a photoacoustic measurement device to solve the above-mentioned problems existing in the prior art. Summary of the Invention

[0004] The purpose of this invention is to provide a method and photoacoustic measurement device for obtaining laser damage threshold, thereby avoiding the time and sample material costs caused by a large number of destructive experiments and improving the detection efficiency of laser damage threshold.

[0005] To achieve the above objective, the method for obtaining the laser damage threshold according to the present invention includes:

[0006] A model for obtaining the laser damage threshold is constructed, which includes an instantaneous damage model and a thermal accumulation damage model. The instantaneous damage model represents the volume heat source distribution, electronic temperature change, lattice temperature change, and stress transmission after a single-pulse laser irradiates the sample material. The thermal accumulation damage model represents the volume heat source distribution, electronic temperature change, and lattice temperature change affected by the environment after a multi-pulse laser irradiates the sample material.

[0007] Obtain the physical property parameters of the material under test and the parameters of the laser source;

[0008] The laser damage threshold is obtained based on the physical property parameters of the material under test, the parameters of the laser source, and the model for obtaining the laser damage threshold.

[0009] The beneficial effects of the method for obtaining the laser damage threshold are as follows: a model for obtaining the laser damage threshold is constructed, the physical property parameters of the material to be tested and the laser source parameters are obtained, and the laser damage threshold is obtained based on the physical property parameters of the material to be tested, the laser source parameters and the model for obtaining the laser damage threshold. This eliminates the need for time and sample material costs caused by a large number of destructive experiments, thereby reducing costs and improving the detection efficiency of the laser damage threshold.

[0010] Optionally, obtaining the laser damage threshold based on the physical property parameters of the material under test, the laser source parameters, and the model for obtaining the laser damage threshold includes:

[0011] Different single-pulse laser source parameters and the physical property parameters of the material under test are input into the instantaneous damage model, wherein each single-pulse laser source parameter corresponds to a single-pulse laser.

[0012] The intensity of a first single-pulse laser is obtained such that the highest lattice temperature of the material under test is equal to the melting point of the material under test; the intensity of a second single-pulse laser is obtained such that the highest electronic temperature of the material under test is equal to the Fermi temperature of the material under test; and the intensity of a third single-pulse laser is obtained such that the maximum equivalent stress of the material under test is equal to the yield strength of the material under test.

[0013] The minimum value among the intensity of the first single-pulse laser, the intensity of the second single-pulse laser, and the intensity of the third single-pulse laser is used as the instantaneous laser damage threshold.

[0014] Optionally, obtaining the laser damage threshold based on the physical property parameters of the material to be tested, the laser source parameters, and the model for obtaining the laser damage threshold further includes:

[0015] Different multi-pulse laser source parameters and the physical property parameters of the material under test are input into the thermal accumulation damage model, wherein each multi-pulse laser source parameter corresponds to a multi-pulse laser.

[0016] The laser irradiation time for each multi-pulse laser is obtained to make the surface temperature of the test material equal to its melting point temperature.

[0017] The intensity of the multi-pulse laser corresponding to the laser irradiation time closest to the measurement period is used as the threshold for thermal accumulation laser damage.

[0018] Optionally, the step of obtaining the laser irradiation time for each multi-pulse laser to make the surface temperature of the material under test equal to the melting point temperature includes:

[0019] Obtain the first curve of the surface temperature of the material under test changing over time for each multi-pulse laser;

[0020] The laser irradiation time required to bring the surface temperature of the test material to equal its melting point temperature is obtained based on the first curve.

[0021] Optionally, obtaining the first curve of the surface temperature of the material under test changing over time for each multi-pulse laser includes:

[0022] The peak value and first time of the surface temperature of the material under test are calculated based on the pulse width, and the valley value and second time of the surface temperature of the material under test are calculated based on the pulse interval.

[0023] Optionally, the first curve obtains the laser irradiation time for each multi-pulse laser to make the surface temperature of the test material equal to its melting point temperature, including:

[0024] The valley value and the second time are fitted to obtain the valley value temperature fitting curve. The valley value temperature fitting curve is added to the average temperature rise value of each irradiation of the corresponding multi-pulse laser to obtain the second curve of the surface temperature of the material under test changing with time under continuous pulse conditions.

[0025] The calculation steps for the average temperature rise include:

[0026] Obtain the peak and valley values ​​of the surface temperature of the material under test corresponding to each pulse;

[0027] Subtract the valley value of the surface temperature of the material under test corresponding to the previous pulse from the peak value of the surface temperature of the material under test corresponding to the subsequent pulse to obtain several temperature rise values.

[0028] The average temperature rise is obtained by averaging several temperature rise values.

[0029] Optionally, obtaining the laser damage threshold based on the physical property parameters of the material to be tested, the laser source parameters, and the model for obtaining the laser damage threshold further includes:

[0030] The minimum value between the instantaneous laser damage threshold and the thermal accumulation laser damage threshold is taken as the laser damage threshold.

[0031] Optionally, the laser source parameters include laser source power and laser pulse width.

[0032] The present invention also provides a photoacoustic measurement device, which includes a laser damage threshold acquisition unit and a laser parameter output module;

[0033] The laser damage threshold acquisition unit is used to execute the laser damage threshold acquisition method to acquire the laser damage threshold;

[0034] The laser parameter output module is used to obtain high signal-to-noise ratio laser source parameters based on the acquired laser damage threshold.

[0035] The beneficial effect of the photoacoustic measurement device is that the laser damage threshold acquisition unit is used to execute the laser damage threshold acquisition method to acquire the laser damage threshold, without the need for time and sample material costs caused by a large number of destructive experiments, thereby reducing costs and improving the detection efficiency of laser damage threshold.

[0036] Optionally, the laser damage threshold acquisition unit includes a model building module, a parameter acquisition module, and a laser damage threshold calculation module. The model building module is used to construct a model for acquiring the laser damage threshold. The model for acquiring the laser damage threshold includes an instantaneous damage model and a thermal accumulation damage model. The instantaneous damage model represents the volumetric heat source distribution, electron temperature change, lattice temperature change, and stress transmission after a single-pulse laser irradiates the sample material. The thermal accumulation damage model represents the volumetric heat source distribution, electron temperature change, and lattice temperature change affected by the environment after a multi-pulse laser irradiates the sample material. The parameter acquisition module is used to acquire the physical property parameters of the material under test and the laser source parameters. The laser damage threshold calculation module is used to acquire the laser damage threshold based on the physical property parameters of the material under test, the laser source parameters, and the model for acquiring the laser damage threshold. Attached Figure Description

[0037] Figure 1 This is a flowchart of a method for obtaining a laser damage threshold in some embodiments of the present invention;

[0038] Figure 2 This is a schematic diagram showing the highest electronic temperature and highest lattice temperature of the sample material under single-pulse laser irradiation in some embodiments of the present invention;

[0039] Figure 3 This is a schematic diagram of the maximum equivalent stress inside the sample material under single-pulse laser irradiation in some embodiments of the present invention;

[0040] Figure 4 This is a schematic diagram of surface temperature changes in some embodiments of the present invention;

[0041] Figure 5 This is a schematic diagram of the valley temperature fitting curve and the second curve showing the change of the surface temperature of the material under test over time under continuous pulse conditions in some embodiments of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art. The terms "comprising" and similar expressions used herein mean that the element or object preceding the word covers the element or object listed following the word and its equivalents, but do not exclude other elements or objects.

[0043] To address the problems existing in the prior art, embodiments of the present invention provide a method for obtaining a laser damage threshold, applied to femtosecond lasers. (Refer to...) Figure 1 The method for obtaining the laser damage threshold includes the following steps:

[0044] S1: Construct a model for obtaining the laser damage threshold. The model for obtaining the laser damage threshold includes an instantaneous damage model and a thermal accumulation damage model. The instantaneous damage model represents the volume heat source distribution, electronic temperature change, lattice temperature change, and stress transmission after a single-pulse laser irradiates the sample material. The thermal accumulation damage model represents the volume heat source distribution, electronic temperature change, and lattice temperature change affected by the environment after a multi-pulse laser irradiates the sample material.

[0045] S2: Obtain the physical property parameters of the material to be tested and the parameters of the laser source;

[0046] S3: Obtain the laser damage threshold based on the physical property parameters of the material to be tested, the laser source parameters, and the model for obtaining the laser damage threshold.

[0047] Specifically, the instantaneous damage model and the thermal accumulation damage model represent the volumetric heat source distribution after single-pulse or multi-pulse laser irradiation of the sample material using a volumetric heat source distribution formula, which is:

[0048]

[0049] The instantaneous damage model and the thermal accumulation damage model express the change in electron temperature of the sample material after irradiation by a single-pulse laser or a multi-pulse laser using an electron temperature change formula, which is:

[0050]

[0051] The instantaneous damage model uses a lattice temperature change formula to represent the lattice temperature change of the sample material after single-pulse laser irradiation. The lattice temperature change formula is as follows:

[0052]

[0053] The instantaneous damage model uses a stress transmission formula to represent the stress transmission of the sample material after single-pulse laser irradiation. The stress transmission formula is as follows:

[0054]

[0055] The lattice temperature change is mainly affected by the ambient temperature. When only the ambient temperature is considered, the thermal accumulation damage model expresses the lattice temperature change of the sample material after multi-pulse laser irradiation by the environment through a formula for the lattice temperature change affected by the environment. The formula for the lattice temperature change affected by the ambient temperature is as follows:

[0056] and Q ext =h·T ext -T l .

[0057] Where Q represents the volumetric heat source distribution, β represents a constant, δ represents the absorptivity of the sample material to the laser, J0 represents the single-pulse energy of the laser, and t p The pulse width of the laser, z s C represents the absorption depth of the laser light by the sample material. e C represents the electronic heat capacity of the sample material. l T represents the lattice heat capacity of the sample material. e T represents the electronic temperature of the sample material. l The sample material represents the lattice temperature, G represents the electron-phonon coupling coefficient of the sample material, and u represents the lattice temperature. zLet ρ represent the displacement along the z-axis, ρ represent the density of the sample material, B represent the bulk modulus of the sample material, υ represent the Poisson's ratio of the sample material, α represent the coefficient of thermal expansion of the sample material, and κ represent the displacement along the z-axis. e Q represents electronic thermal conductivity. ext This represents the convective heat dissipation term, where h represents the heat transfer coefficient of air, and T ext The variable represents ambient temperature, t represents time, and z represents the axis direction. This represents the partial derivative.

[0058] Therefore, the constructed instantaneous damage model can analyze the instantaneous damage of single-pulse lasers from multiple dimensions, including volumetric heat source distribution, electron temperature change, lattice temperature change, and stress transmission, and can accurately obtain the instantaneous damage threshold of a single pulse. The constructed thermal accumulation damage model can analyze the thermal accumulation damage of continuous pulses based on the calculation results of multiple / finitely many pulses, from multiple dimensions such as volumetric heat source distribution, electron temperature change, and lattice temperature change influenced by the environment, thus improving efficiency and accurately obtaining the thermal accumulation damage.

[0059] In some embodiments, obtaining the laser damage threshold based on the physical property parameters of the material under test, the laser source parameters, and the model for obtaining the laser damage threshold includes:

[0060] Different single-pulse laser source parameters and the physical property parameters of the material under test are input into the instantaneous damage model, wherein each single-pulse laser source parameter corresponds to a single-pulse laser.

[0061] The intensity of a first single-pulse laser is obtained such that the highest lattice temperature of the material under test is equal to the melting point of the material under test; the intensity of a second single-pulse laser is obtained such that the highest electronic temperature of the material under test is equal to the Fermi temperature of the material under test; and the intensity of a third single-pulse laser is obtained such that the maximum equivalent stress of the material under test is equal to the yield strength of the material under test.

[0062] The minimum value among the intensity of the first single-pulse laser, the intensity of the second single-pulse laser, and the intensity of the third single-pulse laser is used as the instantaneous laser damage threshold.

[0063] As can be seen, the above embodiments more accurately analyze all factors that cause transient laser damage, and can analyze the transient damage caused by single-pulse laser from three dimensions, thereby obtaining a more precise transient laser damage threshold.

[0064] Specifically, the physical property parameters of the material under test include the absorption rate of the material under test to laser, the absorption depth of the material under test to laser, the electronic heat capacity of the material under test, the lattice heat capacity of the material under test, the electronic thermal conductivity of the material under test, the electronic phonon coupling coefficient of the material under test, the density of the material under test, the bulk modulus of the material under test, the Poisson's ratio of the material under test, and the coefficient of thermal expansion of the material under test. The laser source parameters include the laser source power and the laser pulse width. By substituting the physical property parameters of the material under test and the source parameters of the single-pulse laser into the various formulas of the instantaneous damage model, and adjusting the laser source power (i.e., adjusting the laser intensity), the highest electronic temperature, the maximum equivalent stress of the material under test under the corresponding single-pulse laser intensity can be obtained.

[0065] Figure 2 This is a schematic diagram showing the highest electronic temperature and highest lattice temperature of the sample material under single-pulse laser irradiation in some embodiments of the present invention. Figure 3 This diagram illustrates the maximum equivalent stress inside a sample material under single-pulse laser irradiation in some embodiments of the present invention. A 500nm thick copper thin film is used as the test material, with a laser source power range of 0–650mW and a laser pulse width of 270fs. By substituting the physical property parameters of the copper thin film and the source parameters of the single-pulse laser into the formulas of the instantaneous damage model, the highest electron temperature, highest lattice temperature, and maximum equivalent stress of the copper thin film under the current single-pulse laser source power can be obtained. Then, by adjusting the single-pulse laser source power, the highest electron temperature, highest lattice temperature, and maximum equivalent stress of the copper thin film under different single-pulse laser source powers can be obtained, such as… Figure 2 and Figure 3 As shown in the figure. The power of the laser source of the single-pulse laser determines the intensity of the single-pulse laser.

[0066] Reference Figure 2 and Figure 3 The intensity of a single-pulse laser was obtained by measuring the following: the intensity of a single-pulse laser that makes the highest lattice temperature of the copper thin film equal to its melting point; the intensity of a single-pulse laser that makes the highest electron temperature of the copper thin film equal to its Fermi temperature; and the intensity of a single-pulse laser that makes the maximum equivalent stress of the copper thin film equal to its yield strength. The minimum value among these three intensities was used as the instantaneous laser damage threshold. The instantaneous laser damage threshold of the copper thin film was measured to be 8.644 × 10⁻⁶. 12 W / cm 2The above embodiments are only illustrated using copper thin films as an example. For different materials, the above scheme can also yield more accurate instantaneous laser damage thresholds.

[0067] Under prolonged / continuous pulse irradiation by a pulsed laser, the sample will experience continuous pulse thermal accumulation damage. For continuous pulse thermal accumulation damage, some embodiments provide thermal accumulation damage models. The laser damage threshold is obtained based on the physical property parameters of the material under test, the laser source parameters, and the model for obtaining the laser damage threshold, and further includes:

[0068] Different multi-pulse laser source parameters and the physical property parameters of the material under test are input into the thermal accumulation damage model, wherein each multi-pulse laser source parameter corresponds to a multi-pulse laser.

[0069] The laser irradiation time for each multi-pulse laser is obtained to make the surface temperature of the test material equal to its melting point temperature.

[0070] The intensity of the multi-pulse laser corresponding to the laser irradiation time closest to the measurement period is used as the thermal accumulation laser damage threshold. The measurement period is the period used to measure the thickness of the material under test.

[0071] In some embodiments, the step of obtaining the laser irradiation time for each multi-pulse laser to make the surface temperature of the test material equal to its melting point temperature includes:

[0072] Obtain the first curve of the surface temperature of the material under test changing over time for each multi-pulse laser;

[0073] The laser irradiation time required to bring the surface temperature of the test material to equal its melting point temperature is obtained based on the first curve.

[0074] In some embodiments, obtaining the first curve of the surface temperature of the material under test changing over time for each multi-pulse laser includes:

[0075] The peak value and first time of the surface temperature of the material under test are calculated based on the pulse width, and the valley value and second time of the surface temperature of the material under test are calculated based on the pulse interval.

[0076] In some embodiments, the first curve acquires the laser irradiation time for each multi-pulse laser to make the surface temperature of the test material equal to its melting point temperature, including:

[0077] The valley value and the second time are fitted to obtain the valley value temperature fitting curve. The valley value temperature fitting curve is added to the average temperature rise value of each irradiation of the corresponding multi-pulse laser to obtain the second curve of the surface temperature of the material under test changing with time under continuous pulse conditions.

[0078] The calculation steps for the average temperature rise include:

[0079] The peak and valley values ​​of the surface temperature of the material under test corresponding to each laser pulse are obtained;

[0080] Subtract the valley value of the surface temperature of the material under test corresponding to the previous pulse from the peak value of the surface temperature of the material under test corresponding to the subsequent pulse to obtain several temperature rise values.

[0081] The average temperature rise is obtained by averaging several temperature rise values. Since there are no pulses before the first pulse, the valley value of the surface temperature of the material under test corresponding to the pulse preceding the first pulse is the surface temperature of the material under test at room temperature. Because the pulse width of a femtosecond laser is very short, the peak pulse width is on the femtosecond level, resulting in sparse peak data. Direct fitting of the variation curve yields low accuracy. By fitting the valley values ​​of the surface temperature, a valley temperature fitting curve is obtained. This valley temperature fitting curve is then added to the average temperature rise value of each irradiation of the corresponding multi-pulse laser to obtain the curve showing the peak surface temperature of the material under test changing over time. This ensures the accuracy of the curve showing the peak surface temperature of the material under test changing over time.

[0082] The solution provided in the above embodiments can fit the thermal accumulation damage curve of continuous pulses by calculating a finite number of pulses, thereby improving the computational efficiency. Furthermore, it can analyze the thermal accumulation damage caused by multi-pulse laser irradiation from the volume heat source distribution, electronic temperature change, and lattice temperature change affected by the environment after multi-pulse laser irradiation of the sample material, while ensuring the computational accuracy. Therefore, it can quickly and accurately obtain the thermal accumulation damage threshold caused by continuous pulses.

[0083] Figure 4 This is a schematic diagram of surface temperature changes in some embodiments of the present invention. A 500nm thick copper thin film is used as the test material. The laser source power range is 0–650mW, the laser pulse width is 270fs, and the multi-pulse laser consists of 10 consecutive pulses with a time interval of 18ns between each pulse. By substituting the physical property parameters of the copper thin film and the source parameters of the multi-pulse laser into the various formulas of the heat accumulation damage model, the surface temperature change curve of the copper thin film under the current multi-pulse laser source power can be obtained, as shown below. Figure 4 As shown in the figure. Here, surface temperature refers to the surface lattice temperature.

[0084] Figure 5 This is a schematic diagram of the valley temperature fitting curve and the second curve showing the change of the surface temperature of the material under test over time under continuous pulse conditions in some embodiments of the present invention. Figure 4The surface temperature of the copper thin film was fitted with 10 valley values ​​and the corresponding times to obtain... Figure 5 The valley temperature fitting curve is shown. Figure 5 The valley temperature fitting curve shown is... Figure 4 The average temperature rise of the surface of the copper thin film shown is added together to obtain... Figure 5 The curve showing the peak surface temperature of the copper thin film versus time is shown. The intensity of the multi-pulse laser corresponding to the laser irradiation time closest to the measurement period, where the copper thin film surface temperature equals the melting point temperature, is determined as the thermal accumulation laser damage threshold. The intensity of the multi-pulse laser is determined by the laser source power.

[0085] In some embodiments, obtaining the laser damage threshold based on the physical property parameters of the material under test, the laser source parameters, and the model for obtaining the laser damage threshold further includes: using the minimum value between the instantaneous laser damage threshold and the thermally accumulated laser damage threshold as the laser damage threshold. Wherein, if the instantaneous laser damage threshold is equal to the thermally accumulated laser damage threshold, then both the instantaneous laser damage threshold and the thermally accumulated laser damage threshold are used as the minimum value.

[0086] The present invention also provides a photoacoustic measurement device, which includes a laser damage threshold acquisition unit and a laser parameter output module;

[0087] The laser damage threshold acquisition unit is used to execute the laser damage threshold acquisition method to acquire the laser damage threshold;

[0088] The laser parameter output module is used to obtain high signal-to-noise ratio laser source parameters based on the acquired laser damage threshold. Using the method disclosed in the above embodiments, the laser damage of the sample under test can be accurately obtained, and the laser damage threshold of different materials can be acquired. While avoiding damage to the sample under test, it ensures that the source parameters (such as power) are as close to the limit as possible without damage, thereby further improving the signal quality of laser ultrasonic measurement. Laser damage threshold prediction in the laser ultrasonic measurement process has been achieved for sample materials with different physical properties. The prediction process is fast and efficient, saving a significant amount of time and material costs, and contributing to the further development and application of laser ultrasonic measurement.

[0089] In some embodiments, the laser damage threshold acquisition unit includes a model building module, a parameter acquisition module, and a laser damage threshold calculation module. The model building module is used to construct a model for acquiring the laser damage threshold. The model for acquiring the laser damage threshold includes an instantaneous damage model and a thermal accumulation damage model. The instantaneous damage model represents the internal volumetric heat source distribution, electron temperature change, lattice temperature change, and stress transmission of the sample material after single-pulse laser irradiation. The thermal accumulation damage model represents the volumetric heat source distribution, electron temperature change, and lattice temperature change affected by the environment after multi-pulse laser irradiation of the sample material. The parameter acquisition module is used to acquire the physical property parameters of the material under test and the laser source parameters. The laser damage threshold calculation module is used to acquire the laser damage threshold based on the physical property parameters of the material under test, the laser source parameters, and the model for acquiring the laser damage threshold.

[0090] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A method for obtaining a laser damage threshold, characterized in that, include: A model for obtaining the laser damage threshold is constructed, comprising an instantaneous damage model and a thermal accumulation damage model. The instantaneous damage model represents the volumetric heat source distribution, electron temperature change, lattice temperature change, and stress transmission after a single-pulse laser irradiates the sample material, and is used to obtain the instantaneous laser damage threshold. The thermal accumulation damage model represents the volumetric heat source distribution, electron temperature change, and lattice temperature change affected by the environment after a multi-pulse laser irradiates the sample material, and is used to obtain the thermal accumulation laser damage threshold. Obtain the physical property parameters of the material under test and the parameters of the laser source; The laser damage threshold is obtained based on the physical property parameters of the material under test, the laser source parameters, and the model for obtaining the laser damage threshold. The laser damage threshold is the minimum value between the instantaneous laser damage threshold and the thermal accumulation laser damage threshold. The step of obtaining the laser damage threshold based on the physical property parameters of the material under test, the laser source parameters, and the model for obtaining the laser damage threshold includes: Different single-pulse laser source parameters and the physical property parameters of the material under test are input into the instantaneous damage model, wherein each single-pulse laser source parameter corresponds to a single-pulse laser. The intensity of a first single-pulse laser is obtained such that the highest lattice temperature of the material under test is equal to the melting point of the material under test; the intensity of a second single-pulse laser is obtained such that the highest electronic temperature of the material under test is equal to the Fermi temperature of the material under test; and the intensity of a third single-pulse laser is obtained such that the maximum equivalent stress of the material under test is equal to the yield strength of the material under test. The minimum value among the intensity of the first single-pulse laser, the intensity of the second single-pulse laser, and the intensity of the third single-pulse laser is used as the instantaneous laser damage threshold. Different multi-pulse laser source parameters and the physical property parameters of the material under test are input into the thermal accumulation damage model, wherein each multi-pulse laser source parameter corresponds to a multi-pulse laser. The laser irradiation time for each multi-pulse laser is obtained to make the surface temperature of the test material equal to its melting point temperature. The intensity of the multi-pulse laser corresponding to the laser irradiation time closest to the measurement period is used as the threshold for thermal accumulation laser damage.

2. The method for obtaining the laser damage threshold according to claim 1, characterized in that, The step of obtaining the laser irradiation time for each multi-pulse laser to make the surface temperature of the material under test equal to its melting point includes: Obtain the first curve of the surface temperature of the material under test changing over time for each multi-pulse laser; The laser irradiation time required to bring the surface temperature of the test material to equal its melting point temperature is obtained based on the first curve.

3. The method for obtaining a laser damage threshold according to claim 2, wherein obtaining the first curve of the surface temperature of the material under test corresponding to each multi-pulse laser as a function of time includes: The peak value and first time of the surface temperature of the material under test are calculated based on the pulse width, and the valley value and second time of the surface temperature of the material under test are calculated based on the pulse interval.

4. The method for obtaining the laser damage threshold according to claim 3, characterized in that, The first curve obtains the laser irradiation time for each multi-pulse laser to make the surface temperature of the test material equal to its melting point temperature, including: The valley value and the second time are fitted to obtain the valley value temperature fitting curve. The valley value temperature fitting curve is added to the average temperature rise value of each irradiation of the corresponding multi-pulse laser to obtain the second curve of the surface temperature of the material under test changing with time under continuous pulse conditions. The calculation steps for the average temperature rise include: Obtain the peak and valley values ​​of the surface temperature of the material under test corresponding to each pulse; Subtract the valley value of the surface temperature of the material under test corresponding to the previous pulse from the peak value of the surface temperature of the material under test corresponding to the subsequent pulse to obtain several temperature rise values. The average temperature rise is obtained by averaging several temperature rise values.

5. The method for obtaining the laser damage threshold according to claim 1, characterized in that, The laser source parameters include laser source power and laser pulse width.

6. A photoacoustic measuring device, characterized in that, The photoacoustic measurement device includes a laser damage threshold acquisition unit and a laser parameter output module; The laser damage threshold acquisition unit is used to perform the laser damage threshold acquisition method as described in any one of claims 1 to 5, to acquire the laser damage threshold; The laser parameter output module is used to obtain high signal-to-noise ratio laser source parameters based on the acquired laser damage threshold.

7. The photoacoustic measuring device according to claim 6, characterized in that, The laser damage threshold acquisition unit includes a model building module, a parameter acquisition module, and a laser damage threshold calculation module. The model building module is used to construct a model for acquiring the laser damage threshold. The model for acquiring the laser damage threshold includes an instantaneous damage model and a thermal accumulation damage model. The instantaneous damage model represents the volumetric heat source distribution, electron temperature change, lattice temperature change, and stress transmission after a single-pulse laser irradiates the sample material. The thermal accumulation damage model represents the volumetric heat source distribution, electron temperature change, and lattice temperature change affected by the environment after a multi-pulse laser irradiates the sample material. The parameter acquisition module is used to acquire the physical property parameters of the material under test and the laser source parameters. The laser damage threshold calculation module is used to acquire the laser damage threshold based on the physical property parameters of the material under test, the laser source parameters, and the model for acquiring the laser damage threshold.

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