Method for predicting laser irradiation life of coated optical element

Abstract

The invention discloses a method for predicting the laser irradiation life of a coated optical element. The method comprises the following steps: obtaining the content of structural defects; calculating temperature and stress; obtaining the multiplication law of the internal defect content of the optical element in the laser irradiation process; calculating a mean value and a standard deviation of the damage threshold; and calculating a damage criterion and a life value. According to the method, the critical condition of failure of the coated optical element can be accurately determined on the basis of the 1-on-1 damage threshold test in combination with the simulation model under laser irradiation, so that a theoretical basis and technical support are provided for life evaluation of the coated optical element. According to the method, the defect proliferation model of the coated optical element is constructed based on the Arrhenius formula, the multi-pulse laser irradiation thermal-mechanical coupling simulation model considering defect evolution is established, the evolution rule of the temperature and stress of the element under the action of different laser parameters can be calculated, and the life prediction of the coated optical element is realized; the problems that a traditional experience statistical method is high in experiment cost and low in prediction precision are effectively solved.

Description

Technical Field

[0001] The present invention belongs to the field of damage life prediction of coated optical elements, and in particular relates to a method for predicting the laser irradiation life of coated optical elements using temperature or stress as damage criterion. Background Art

[0002] The lifetime of a coated optical component refers to the cumulative time or number of pulses during which it maintains stable optical performance and does not suffer functional damage under laser irradiation conditions of a certain energy density. In high-power laser systems, all optical components will gradually degrade due to long-term irradiation. Compared with single-pulse irradiation, the laser damage threshold of coated optical components will gradually decrease when subjected to multi-pulse laser irradiation at a sub-damage threshold energy density. This phenomenon is generally referred to as the "optical fatigue effect." Due to the existence of the optical fatigue effect, the performance of coated optical components may deteriorate during long-term use, resulting in a decrease in the output power of the laser system and even causing system failure or shutdown. Therefore, accurately predicting the lifetime of coated optical components is crucial for the optimal design of laser systems and avoiding catastrophic failures. However, there is still a lack of methods for predicting the lifetime of coated optical components.

[0003] During laser irradiation, coated optical components absorb laser energy, generating significant heat accumulation, leading to localized temperature increases. Due to differences in thermal properties such as the coefficient of thermal expansion and thermal conductivity among the film layers and the substrate material, temperature rise and temperature gradients cause varying amounts of thermal expansion and contraction, generating thermal stress. When the accumulated temperature reaches the material's melting point, or when thermal stress accumulates and exceeds the film's strength, the film may crack or delaminate, ultimately leading to failure of the optical film.

[0004] Chinese patent CN112326197A discloses a "method for predicting the lifespan of laser optical components." This invention utilizes a combination of high-repetition-rate lasers and target lasers to determine the relationship between the laser damage threshold and pulse number at high repetition rates, as well as the compensation factor. This method calculates the lifespan of optical components at any laser flux, significantly shortening the lifespan test cycle. However, this invention requires extensive experimentation to determine the appropriate compensation factor to achieve the lifespan prediction goal, resulting in high experimental and time costs.

[0005] Chinese patent CN108303239A discloses a "Method for Accelerated Testing and Prediction of Laser Optical Component Lifetime." This invention uses the number of shots or time as the independent variable and the lifetime probability as the dependent variable to fit a lifetime probability function for large-aperture optical components under specific laser parameters. By varying the laser irradiation flux, lifetime probability curves are obtained under different flux conditions, and further fitting a lifetime flux function under specific lifetime probabilities is performed, thereby enabling accelerated lifetime testing of laser optical components. This method shortens the testing cycle, but the lifetime function requires numerous fitting parameters and relies on high-quality experimental data. Insufficient or biased data can reduce prediction accuracy.

[0006] Chinese patent CN118819905A discloses a "method for assessing the lifetime reliability of optical components and access systems." This invention analyzes failure factors, determines lifetime characteristic parameters, and fits lifetime distributions based on lifetime data to achieve reliability assessment of optical components. A reliability model is then established based on the system structure, and Monte Carlo simulation is used to assess the reliability of the access system and identify weak links, thereby improving the accuracy and reliability of the assessment. While this method can assess reliability within a specified timeframe, it struggles to predict the cumulative effects of long-term use, such as material aging and performance degradation.

[0007] As mentioned in the review, predicting the long-term service life of coated optical components will require a large number of experiments, which will increase the experimental costs. While the reliability analysis method can improve the prediction accuracy, it is difficult to reflect the failure mechanism of coated optical components and still has limitations in applicability and accuracy. Summary of the Invention

[0008] In order to solve the problems of high experimental cost and low prediction accuracy in the lifetime prediction of coated optical components in the prior art, the present invention provides a method for predicting the laser irradiation lifetime of coated optical components, which can achieve efficient and low-cost prediction of the lifetime of coated optical components.

[0009] In order to achieve the above object, the technical solution of the present invention is as follows:

[0010] A method for predicting the laser irradiation life of a coated optical component comprises the following steps:

[0011] A. Obtaining structural defect content

[0012] The atomic structure defect content is obtained by quantitatively analyzing the spectrum of optical components under irradiation with different laser parameters.

[0013] B. Calculate temperature and stress

[0014] Temperature and stress are calculated using a coupled thermal-mechanical simulation model of coated optical components exposed to multi-pulse laser irradiation.

[0015] C. Obtain the proliferation law of internal defect content of optical components during laser irradiation

[0016] Based on the structural defect content change results obtained in step A and the temperature and stress results obtained by simulation in step B, a defect proliferation model of the coated optical element is established to obtain the proliferation law of the internal defect content of the optical element during laser irradiation.

[0017] D. Calculate the mean and standard deviation of the damage threshold.

[0018] E. Calculate damage criteria and life value.

[0019] F. Verify the accuracy and effectiveness of life prediction results

[0020] Perform a linear fit on the lifetime obtained in step E to obtain a 3σ confidence interval and prediction interval. Conduct multi-pulse laser irradiation experiments and record the number of pulses at which damage occurs on the coated optical component under different energy densities. Observe whether the multi-pulse laser irradiation data falls within the prediction interval to verify the accuracy and effectiveness of the lifetime prediction model.

[0021] Furthermore, the laser parameters in step A include the number of pulses, energy density and repetition frequency, and the spectrum includes photoluminescence spectrum, cathode fluorescence spectrum, transient fluorescence spectrum, Raman spectrum and absorption spectrum.

[0022] Furthermore, the method for calculating temperature and stress in step B is as follows:

[0023] A two-dimensional axisymmetric geometric model was established. The film structure of the optical element was modeled using the "Thin Layer" interface and the Multilayer Material module in the finite element software, with corresponding dimensional parameters and meshing settings. Thermophysical properties of the film and substrate materials were assigned, including the absorption coefficient α, thermal expansion coefficient γ, elastic modulus E, Poisson's ratio ν, and thermal conductivity k. Boundary conditions and laser parameters were applied, and multi-physics coupling between the Solid Heat Transfer and Solid Mechanics modules was employed to calculate temperature and stress using a thermal-mechanical coupled simulation model of the coated optical element under multi-pulse laser irradiation. This thermal-mechanical coupled simulation model of the coated optical element under multi-pulse laser irradiation is referred to as the combined simulation model.

[0024] Furthermore, the defect proliferation model in step C is established based on the Arrhenius formula and is expressed as follows:

[0025]

[0026] Where t is the laser irradiation time, A is the pre-exponential factor, R is the gas constant, T is the laser irradiation temperature, σ is the thermal stress of the laser irradiation, V is the activation volume of the laser irradiation area, k is the Boltzmann constant, and E is the activation volume of the laser irradiation area. a is the activation energy of defects in optical components, E b is the activation energy of defect recovery in optical components, and dn / dt is the defect growth rate.

[0027] Furthermore, the method for calculating the mean and standard deviation in step D is as follows:

[0028] Based on the ISO 21254 standard, a damage threshold test bench was used to conduct a one-on-one damage threshold test on coated optical components. The energy density at which the probability of damage is zero is defined as the damage threshold of the coated optical component. Considering the discrete nature of the sample, multiple measurement points were selected, and the damage thresholds were tested for normal distribution. The mean and standard deviation of the damage thresholds were calculated.

[0029] Furthermore, the method for calculating the damage criterion in step E is as follows: inputting the mean value of the damage threshold into a thermal-mechanical coupling simulation model of a coated optical element irradiated by multiple pulses of laser light, and using the mean value of the damage threshold as the initial laser energy density, calculating the temperature or stress under single-pulse irradiation through the thermal-mechanical coupling simulation model of the coated optical element under multiple pulses of laser light irradiation, and using the temperature or stress as the damage criterion;

[0030] The temperature includes the maximum temperature T of the substrate material 1,max and the maximum temperature T within the film material 2,max When the temperature reaches any maximum value during laser irradiation, the optical element will be damaged; the stress includes the maximum normal stress of the interface Maximum shear stress Maximum tensile stress and maximum shear stress in the film The maximum tensile stress in the film layer includes radial stress Circular and axial stress When the stress reaches any maximum value during laser irradiation, the optical element will be damaged.

[0031] On this basis, the laser energy density is gradually reduced, and the simulation model is used to calculate the temperature and stress evolution inside the coated optical component under different laser parameter conditions, until the temperature or stress accumulation reaches the damage criterion. The lifetime is defined as the number of laser pulses experienced when the temperature or stress inside the optical component first reaches the damage criterion under a certain laser energy density.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. Based on a 1-on-1 damage threshold test and combined with a simulation model under laser irradiation, this invention can accurately determine the critical conditions for failure of coated optical components, thereby providing a theoretical basis and technical support for the life assessment of coated optical components.

[0034] 2. The present invention constructs a defect proliferation model for coated optical components based on the Arrhenius formula, and further establishes a multi-pulse laser irradiation thermal-mechanical coupling simulation model that takes into account defect evolution. It can calculate the evolution law of component temperature and stress under different laser parameters, and realize the life prediction of coated optical components, effectively overcoming the shortcomings of traditional empirical statistical methods such as high experimental cost and low prediction accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Flowchart of the multi-pulse laser lifetime prediction method for coated optical components considering defect evolution.

[0036] Figure 2 The 3σ prediction interval given by the lifetime prediction model and the corresponding lifetime experimental results under two different laser energy flux conditions. DETAILED DESCRIPTION

[0037] To make the objectives, technical solutions, and advantages of the present invention more clear, the following will provide a more complete description of the present invention with reference to the accompanying drawings and embodiments. It should be understood that the embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. All other embodiments obtained by persons of ordinary skill in the art without creative effort are intended to fall within the scope of protection of the present invention.

[0038] like Figure 1 As shown, the method for predicting the laser irradiation life of a coated optical component includes the following steps:

[0039] Step 1: Conduct laser irradiation experiments on optical components under different parameters, and use photoluminescence spectroscopy, cathodoluminescence spectroscopy, transient fluorescence spectroscopy, Raman spectroscopy, and absorption spectroscopy to measure the optical component spectra before and after irradiation to obtain the results of changes in the content of atomic structural defects;

[0040] The structural defect content is characterized by photoluminescence spectroscopy, cathodoluminescence spectroscopy, transient fluorescence spectroscopy, Raman spectroscopy and absorption spectroscopy. The characteristic emission peak at 650 nm in the fluorescence spectrum or the characteristic absorption peak at 258 nm in the absorption spectrum is quantitatively analyzed to obtain the content of non-bridging oxygen vacancy center (NBOHC) defects.

[0041] Step 2: Establish a 2D axisymmetric geometry model and use the "Thin Layer" interface and multilayer material module in the finite element software COMSOL to model the membrane structure of the component. The calculation domain is set to 2mm in the z direction and 6mm in the r direction. The mesh of the laser irradiation area is encrypted with 50 elements and a cell ratio of 6. 。For the nanoscale membrane layer, the unit size is set to ultrafine, with 10 units per layer. The model is assigned thermal physical parameters such as the absorption coefficient α, thermal expansion coefficient γ, elastic modulus E, Poisson's ratio ν, and thermal conductivity k of the membrane layer and substrate material.

[0042] Here, the absorption coefficient is calculated from the imaginary part of the refractive index measured by ellipsometer, the elastic modulus E is measured by nanoindentation, and the remaining thermodynamic parameters are directly set according to the parameters of the material library;

[0043] Set the surface and bottom of the component for flow and radiation, and set the side boundary temperature to room temperature T. By coupling solid heat transfer with solid mechanics, establish a thermal-mechanical coupling simulation model for multi-pulse laser-irradiated thin-film optical components. Perform simulation calculations based on the parameters of the laser irradiation experiment in step 1 to obtain the temperature and stress under the corresponding laser parameters.

[0044] The laser parameters are laser energy density F, frequency f and irradiation time t, and the temperature and stress are obtained by simulation model calculation;

[0045] Step 3: During laser irradiation, chemical bonds in the damaged precursor in SiO2 are broken, generating NBOHC defects. Based on the changes in structural defect content obtained during laser irradiation in Step 1 and the temperature and stress results obtained from simulation in Step 2, a defect evolution model for optical components under laser irradiation is established based on the Arrhenius equation, revealing the evolution of the internal defect content of optical components over time during laser exposure.

[0046]

[0047] Right now:

[0048]

[0049] in,

[0050] Where, E a =0.64eV, E b =0.52eV, Frequency factor A and the total number of structures participating in the reaction n max is the fitting parameter.

[0051] Step 4: Perform a 1-on-1 damage threshold test on the coated optical component using a damage threshold test bench according to ISO 21254. Considering the discreteness of the sample, multiple points are selected for measurement and a normal distribution test is performed on them to calculate their mean and standard deviation.

[0052] The 1-on-1 damage threshold test is the highest laser energy density at which the probability of damage to the optical element is zero.

[0053] Step 5: Input the laser parameters from step 4 into a thermal-mechanical coupling simulation model of a multi-pulse laser irradiated coated optical element, and use the average value of the damage threshold as the initial laser energy density. Calculate the temperature or stress under single-pulse irradiation through the thermal-mechanical coupling simulation model of the coated optical element under multi-pulse laser irradiation, and use this as the damage criterion;

[0054] The criterion is the maximum temperature T of the substrate material 1,max , the maximum temperature T in the film material 2,max When the temperature reaches any maximum value after the irradiation process, the optical element will be damaged, and the maximum normal stress of the interface Maximum shear stress Maximum tensile stress and maximum shear stress in the film The maximum tensile stress in the film layer includes radial stress Circular and axial stress When the stress reaches any maximum value during laser irradiation, the optical element will be damaged.

[0055] On this basis, the laser energy density is reduced in sequence, and the temperature or stress evolution process under different laser energy densities is calculated until the coated optical element reaches the life fatigue limit, and the calculation is stopped;

[0056] The lifetime is the number of pulses when the temperature or stress reaches the damage criterion at a certain laser energy density;

[0057] Step 6: Perform linear fitting on the life of the coated optical component to obtain the 3σ confidence interval and prediction interval. Carry out multi-pulse laser irradiation experiments under two laser energy densities and record the number of pulses when damage to the coated optical component occurs. The life obtained from the laser experiment falls completely within the life prediction interval, such as Figure 2 As shown in Figure 3, it is shown that the lifetime prediction model considering defect proliferation can better predict the lifetime of coated optical components.

[0058] The present invention is not limited to this embodiment, and any equivalent concepts or modifications within the technical scope disclosed by the present invention are included in the protection scope of the present invention.

Claims

1. A method for predicting the laser irradiation life of a coated optical component, characterized by: The steps include: A. Obtaining structural defect content The atomic structure defect content is obtained by quantitatively analyzing the spectrum of optical components irradiated with different laser parameters; B. Calculate temperature and stress Calculate the temperature and stress of coated optical components under multi-pulse laser irradiation through a thermal-mechanical coupling simulation model; C. Obtain the proliferation law of internal defect content of optical components during laser irradiation Based on the structural defect content variation results obtained in step A and the temperature and stress results obtained by simulation in step B, a defect proliferation model for the coated optical component is established to obtain the proliferation law of the internal defect content of the optical component during laser irradiation; D. Calculate the mean and standard deviation of the damage threshold; E. Calculate damage criteria and life value; F. Verify the accuracy and effectiveness of life prediction results Perform linear fitting on the lifetime obtained in step E to obtain the 3σ confidence interval and prediction interval; conduct multi-pulse laser irradiation experiments and record the number of pulses when damage occurs to the coated optical components under different energy density conditions; observe whether the multi-pulse laser irradiation experimental data falls within the prediction interval to verify the accuracy and effectiveness of the lifetime prediction model.

2. The method for predicting the laser irradiation lifetime of a coated optical component according to claim 1, characterized in that: The laser parameters in step A include the number of pulses, energy density and repetition frequency, and the spectrum includes photoluminescence spectrum, cathode fluorescence spectrum, transient fluorescence spectrum, Raman spectrum and absorption spectrum.

3. The method for predicting the laser irradiation lifetime of a coated optical component according to claim 1, characterized in that: The method for calculating temperature and stress in step B is as follows: A two-dimensional axisymmetric geometric model was established. The film structure of the optical element was modeled using the "thin layer" interface and multilayer material module in the finite element software, and the corresponding dimensional parameters and mesh division were set. The film layer and the substrate material were assigned thermophysical parameters, including the absorption coefficient α, thermal expansion coefficient γ, elastic modulus E, Poisson's ratio ν, and thermal conductivity k. Boundary conditions and laser parameters were applied, and the multi-physics field coupling of the solid heat transfer module and the solid mechanics module was used to calculate the temperature and stress through the thermal-mechanical coupling simulation model of the coated optical element under multi-pulse laser irradiation. The thermal-mechanical coupling simulation model of the coated optical element under multi-pulse laser irradiation is referred to as the combined simulation model.

4. The method for predicting the laser irradiation lifetime of a coated optical component according to claim 1, characterized in that: The defect proliferation model in step C is established based on the Arrhenius formula and is expressed as follows: Where t is the laser irradiation time, A is the pre-exponential factor, R is the gas constant, T is the laser irradiation temperature, σ is the thermal stress of the laser irradiation, V is the activation volume of the laser irradiation area, k is the Boltzmann constant, and E is the activation volume of the laser irradiation area. a is the activation energy of defects in optical components, E b is the activation energy of defect recovery in optical components, and dn / dt is the defect growth rate.

5. The method for predicting the laser irradiation lifetime of a coated optical component according to claim 1, characterized in that: The method for calculating the mean and standard deviation in step D is as follows: According to the ISO 21254 standard, a 1-on-1 damage threshold test bench was used to perform damage threshold tests on coated optical components. The energy density at which the damage probability is zero is defined as the damage threshold of the coated optical component. Considering the discreteness of the sample, multiple points were selected for measurement, and the damage threshold was tested for normal distribution. The mean and standard deviation of the damage threshold were calculated.

6. The method for predicting the laser irradiation lifetime of a coated optical component according to claim 1, characterized in that: The method for calculating the damage criterion in step E is as follows: inputting the mean value of the damage threshold into a thermal-mechanical coupling simulation model of a coated optical element irradiated by multiple pulses of laser light, using the mean value of the damage threshold as the initial laser energy density, calculating the temperature or stress under single-pulse irradiation through the thermal-mechanical coupling simulation model of the coated optical element under multiple pulses of laser light, and using the temperature or stress as the damage criterion; The temperature includes the maximum temperature T of the substrate material 1,max and the maximum temperature T within the film material 2,max ,When the temperature reaches any maximum value during laser irradiation, the optical element will be damaged; The stress includes the maximum normal stress of the interface Maximum shear stress Maximum tensile stress and maximum shear stress in the film The maximum tensile stress in the film layer includes radial stress Circular and axial stress When the stress reaches any maximum value during laser irradiation, the optical element will be damaged; On this basis, the laser energy density is lowered successively, and the simulation model is used to calculate the temperature or stress evolution process inside the coated optical component under different laser parameter conditions until the temperature or stress accumulation reaches the damage criterion. The lifetime is defined as the number of laser pulses experienced when the internal temperature or stress of the optical component first reaches the damage criterion under a certain laser energy density condition.

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