Infrared material high-temperature broadband optical constant inversion calculation method
By establishing an optical constant calculation model based on phonon absorption theory and Kramers-transform, and combining multiphonon and singlephonon models, the accuracy problem of optical constants of infrared materials under varying temperature conditions was solved, thus improving the high-temperature design and analysis accuracy of infrared detection systems.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- TIANJIN JINHANG INST OF TECH PHYSICS
- Filing Date
- 2023-09-11
- Publication Date
- 2026-06-16
AI Technical Summary
Existing classical oscillator infrared material optical constant models fail to accurately reflect optical properties under varying temperature conditions, resulting in insufficient precision in the design and analysis of infrared detection systems in high-temperature environments.
An optical constant calculation model was established using phonon absorption theory and Kramers-transform. Combining multiphonon and singlephonon absorption coefficient models, the model parameters were iteratively optimized using numerical optimization methods to calculate the optical constants of infrared materials at high temperatures.
Accurate calculation of the optical constants of infrared materials under high-temperature conditions has been achieved, improving the design and analysis accuracy of infrared detection systems.
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Figure CN117233128B_ABST
Abstract
Description
Technical Field
[0001] This application relates to infrared material optical property analysis technology, specifically to a method for calculating the inversion of high-temperature broadband optical constants of infrared materials. Background Technology
[0002] Infrared materials are primarily used in optical windows and components of infrared detection systems, and their optical properties determine the system's performance. Currently, the demand for infrared detection systems in various high-temperature special environments is increasing. To achieve accurate and effective infrared optical system design, infrared optical thin film design, infrared emissivity characterization, and infrared imaging analysis under high-temperature conditions, the broadband optical constants of infrared materials at high temperatures must possess high accuracy. Material optical constants refer to the refractive index and extinction coefficient of a material. Generally, the refractive index and extinction coefficient of a material are only wavelength-dependent. However, under varying temperature conditions, the refractive index and extinction coefficient of the same material at a given wavelength will change simultaneously with temperature. Conventional classical oscillator infrared material optical constant models based on the Cauchy model, Sellmeier model, and Gaussian model do not include temperature parameters, making it difficult for these models to accurately represent the physical meaning of material optical constants under varying temperature conditions. Summary of the Invention
[0003] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a method for inverting and calculating the high-temperature broadband optical constants of infrared materials, including:
[0004] Select an infrared material and determine the spectral range for inversion calculation; at a preset temperature, test the actual transmittance of the infrared material to each wavelength within the spectral range using a spectrometer;
[0005] Based on phonon absorption theory and Kramers- A transformation is performed to establish an optical constant calculation model for the infrared material. The optical constant calculation model includes multiple model parameters, which are temperature-dependent. The theoretical transmittance of the infrared material to each wavelength in the spectral band at the preset temperature is calculated using the optical constant calculation model.
[0006] With the goal of reducing the error between the theoretical transmittance and the actual transmittance, the model parameters are iteratively optimized within a predetermined range using a numerical optimization method to obtain optimized parameters.
[0007] The optimized parameters are then input into the optical constant calculation model to calculate the actual optical constants of the infrared material.
[0008] The optical constant calculation model according to the technical solution provided in the embodiments of this application includes: a multiphonon absorption coefficient model, a multiphonon refractive index model, a single phonon absorption coefficient model, and a single phonon refractive index model.
[0009] According to the technical solution provided in the embodiments of this application, the calculation process of the theoretical transmittance of the infrared material to each wavelength in the spectral band at a preset temperature includes:
[0010] The multiphonon absorption coefficient of the infrared material for the wavelength is calculated using the multiphonon absorption model; the single-phonon absorption coefficient of the infrared material for the wavelength is calculated using the single-phonon absorption model.
[0011] The theoretical absorption coefficient of the infrared material for the wavelength is obtained by summing the single-phonon absorption coefficient and the multiphonon absorption coefficient.
[0012] The multiphonon refractive index of the infrared material to the wavelength is calculated using the multiphonon refractive index model; the single phonon refractive index of the infrared material to the wavelength is calculated using the single phonon refractive index model.
[0013] The theoretical refractive index of the infrared material for the wavelength is obtained by summing the multiphonon refractive index and the singlephonon refractive index.
[0014] Based on the theoretical absorption coefficient and theoretical refractive index, the theoretical transmittance is obtained through Fresnel's law and the theory of light transmission.
[0015] The establishment of the multiphonon absorption coefficient model according to the technical solution provided in the embodiments of this application includes:
[0016] Establish the nth-order phonon state intensity function S n (ν,T);
[0017] Establish the nth-order phonon state density function ρ n (ν,T);
[0018] Based on the S n (ν,T) and the ρ n (ν,T), the multiphonon absorption coefficient model is established based on multiphonon absorption theory.
[0019] Where ν is the wave number and T is the temperature.
[0020] The establishment of the multiphonon refractive index model according to the technical solution provided in the embodiments of this application includes:
[0021] The nth-order phonon state density function ρ n (ν,T) performs Kramers– Transformation to obtain δn (ν);
[0022] Based on the nth-order phonon state intensity function S n (ν,T) and δ n (ν), thus obtaining the multiphonon refractive index model.
[0023]
[0024] in,
[0025] δ n (ν) represents the Kramers-- The transformed nth-order phonon state density function;
[0026] ν max π is the maximum longitudinal vibration frequency of the crystal lattice, T0 is the mathematical constant π, and T0 is the room temperature.
[0027] α (a / o)11 α (a / o)12 α (a / o)13 All are empirical parameters that include phonon information from both optical and acoustic modes. denoted as the frequency associated with the optical and acoustic modes in the intensity function of the nth-order phonon state.
[0028] The dielectric function ε is obtained based on a single-phonon oscillator model according to the technical solution provided in the embodiments of this application. r Based on the dielectric function ε r Establish the single-phonon absorption coefficient model Based on the dielectric function ε r Establish the single-phonon refractive index model
[0029] The calculation process of theoretical transmittance according to the technical solution provided in the embodiments of this application includes:
[0030] The extinction coefficient is calculated based on the theoretical absorption coefficient.
[0031] Calculate the complex refractive index based on the extinction coefficient and the actual refractive index;
[0032] The first reflectance of light incident from air onto the surface of the infrared material is calculated based on the complex refractive index, and then the first transmittance is calculated. The second reflectance of light exiting from the surface of the infrared material onto air is calculated, and then the second transmittance is calculated.
[0033] The internal transmittance is calculated based on the thickness of the infrared material and the theoretical absorption coefficient.
[0034] The theoretical transmittance is calculated based on the first transmittance, the second transmittance, and the internal transmittance.
[0035] The actual optical constants described in the technical solutions provided in the embodiments of this application include the actual absorption coefficient and actual refractive index of the infrared material for the wavelength.
[0036] According to the numerical optimization method provided in the embodiments of this application, either particle swarm optimization or genetic algorithm is selected.
[0037] The steps of the particle swarm optimization algorithm according to the technical solution provided in the embodiments of this application include:
[0038] Initialize the particle swarm and parameter settings;
[0039] Calculate the objective function value;
[0040] Update individual optimal values and group optimal values;
[0041] Determine if the convergence data is satisfied; if so, output the optimal result and the number of iterations; otherwise, update the position vector and velocity vector of each particle and repeat the iteration process.
[0042] The beneficial effects are:
[0043] Based on phonon absorption theory and Kramers- A transformation is performed to establish an optical constant calculation model for the infrared material. The optical constant calculation model includes multiple model parameters, which are temperature-dependent. Therefore, a temperature-dependent optical constant calculation model is established, enabling the calculation model to calculate the optical constant at a preset temperature, thus making the calculation model more practical.
[0044] The model parameters are iteratively optimized within a predetermined range using numerical optimization methods to obtain optimized parameters. These optimized parameters are then incorporated into the optical constant calculation model to calculate the actual optical constants of the infrared material, thereby making the calculation of the optical constants more accurate. Attached Figure Description
[0045] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:
[0046] Figure 1 The multiphonon refractive index of ZnS at 300℃ is for the spectral range of 2-16 μm in this embodiment of the application.
[0047] Figure 2 The multiphonon refractive index of ZnS at 300℃ is for the spectral range of 2-16 μm in this embodiment of the application.
[0048] Figure 3 The single-phonon absorption coefficient of ZnS at 300℃ with a spectral range of 2-16μm is given in the embodiments of this application.
[0049] Figure 4 The single-phonon refractive index of ZnS at 300℃ is for the spectral range of 2-16μm in this embodiment of the application.
[0050] Figure 5 The theoretical absorption coefficient of ZnS at 300℃ with a spectral range of 2-16μm is given in the embodiments of this application.
[0051] Figure 6 The theoretical refractive index of ZnS at 300℃ with a spectral range of 2-16μm is given in the embodiments of this application.
[0052] Figure 7 The theoretical transmittance, actual transmittance, and transmittance calculated after inversion are for ZnS with a spectral range of 2-16μm and a thickness of 5mm at 300℃ in the embodiments of this application.
[0053] Figure 8 The optical constants (refractive index and extinction coefficient) of ZnS material at 2-16μm and 300℃ after inversion calculation in the spectral range of this application embodiment are 2-16μm and 300℃.
[0054] Figure 9 This is a flowchart of the particle swarm algorithm in an embodiment of this application. Detailed Implementation
[0055] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.
[0056] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.
[0057] Please refer to Figures 1 to 8 A method for inverting and calculating the high-temperature broadband optical constants of infrared materials, comprising:
[0058] Select an infrared material and determine the spectral range for inversion calculation; at a preset temperature, test the actual transmittance of the infrared material to each wavelength within the spectral range using a spectrometer;
[0059] Based on phonon absorption theory and Kramers- A transformation is performed to establish an optical constant calculation model for the infrared material. The optical constant calculation model includes multiple model parameters, which are temperature-dependent. The theoretical transmittance of the infrared material to each wavelength in the spectral band at the preset temperature is calculated using the optical constant calculation model.
[0060] With the goal of reducing the error between the theoretical transmittance and the actual transmittance, the model parameters are iteratively optimized within a predetermined range using a numerical optimization method to obtain optimized parameters.
[0061] The optimized parameters are then input into the optical constant calculation model to calculate the actual optical constants of the infrared material.
[0062] Specifically, the infrared materials include transparent and translucent fluorides, oxides, sulfides, and oxynitrides.
[0063] In this embodiment, the infrared material selected is ZnS (zinc sulfide) with a thickness of d = 5 mm.
[0064] In this embodiment, a spectral band with a wavelength range of 2-16μm is selected, and the preset temperature is 300℃.
[0065] In this embodiment, the spectrometer is an infrared Fourier analyzer spectrometer with a sample high-temperature heating function.
[0066] Specifically, the transmittance of a ZnS material sample with a thickness of d = 5 mm was measured using an infrared Fourier transform spectrometer at a temperature T = 300℃ in the 2-16 μm spectral range. b (ν), the test results are as follows Figure 7 Curve 2 in the diagram.
[0067] Specifically, in the phonon absorption theory, the mechanism of phonon absorption can be described as a discrete quantum process in which lattice vibrations are first excited into a high-energy acoustic mode, then absorb the energy of a photon or other particle, and finally excited into another low-energy acoustic mode.
[0068] Specifically, the Kramers – The transformation is the Cramer-Kronig transformation, which is used to relate the real and imaginary parts of the material's refractive index.
[0069] Furthermore, the Kramers – The transformation converts the imaginary part of the reflection and transmission spectra into the real part of the refractive index, or calculates the imaginary part using the known real part.
[0070] In a preferred embodiment, the optical constant calculation model includes: a multiphonon absorption coefficient model, a multiphonon refractive index model, a single phonon absorption coefficient model, and a single phonon refractive index model.
[0071] In a preferred embodiment, the establishment of the multiphonon absorption coefficient model includes:
[0072] Establish the nth-order phonon state intensity function S n (ν,T);
[0073] Establish the nth-order phonon state density function ρ n (ν,T);
[0074] Based on the S n (ν,T) and the ρ n (ν,T), the multiphonon absorption coefficient model is established based on multiphonon absorption theory.
[0075] Where ν is the wave number and T is the temperature.
[0076] Furthermore,
[0077] nth-order phonon state intensity function S n The expression for (ν,T) is:
[0078]
[0079] nth-order phonon state density function ρ n The expression for (ν,T) is:
[0080]
[0081] Where, k b Here, c is the Boltzmann constant, and m = 0, 1, 2, 3, ..., m. max ≤(J-1) / 2,
[0082] Where h is Planck's constant, D is the dissociation energy, J refers to the phonon state, and Q(T) is the distribution function.
[0083] in,
[0084]
[0085]
[0086]
[0087] in,
[0088]
[0089]
[0090]
[0091] in,
[0092] Φ(nν max -ν) is the step function, and T0 is 293K.
[0093] Among them, a, K, α (a / o)11 α (a / o)12 α (a / o)13 α (a / o)21 α (a / o)22 α (a / o)23 α3 is an empirical parameter, and its value can be found in Table 1.
[0094] Table 1
[0095]
[0096] In a preferred embodiment, the establishment of the multiphonon refractive index model includes:
[0097] The nth-order phonon state density function ρ n (ν,T) performs Kramers– Transformation to obtain δ n (ν);
[0098] Based on the nth-order phonon state intensity function S n (ν,T) and δ n (ν), thus obtaining the multiphonon refractive index model:
[0099]
[0100] in,
[0101] δ n (ν) represents the Kramers-- The transformed nth-order phonon state density function;
[0102] ν max π is the maximum longitudinal vibration frequency of the crystal lattice, T0 is the mathematical constant π, and T0 is the room temperature.
[0103] α (a / o)11 α (a / o)12 α (a / o)13 All are empirical parameters that include phonon information from both optical and acoustic modes. denoted as the frequency associated with the optical and acoustic modes in the intensity function of the nth-order phonon state.
[0104] Specifically, the nth-order phonon state density function ρn (ν,T) performs Kramers Transformation to obtain δ n The specific process of (ν) is as follows:
[0105] nth-order phonon state density function ρ n (ν,T) performs Kramers– The transformation yields:
[0106]
[0107] After multiple approximations, δ n (ν) can be obtained by solving the Dawson integral:
[0108]
[0109] Where D is the Dawson integral process.
[0110] In a preferred embodiment, the dielectric function ε is obtained based on a single-phonon oscillator model. r Based on the dielectric function ε r Establish the single-phonon absorption coefficient model Based on the dielectric function ε r Establish the single-phonon refractive index model
[0111] Specifically, in the single-phonon oscillator model, the dielectric function ε r The expression is:
[0112]
[0113] in,
[0114]
[0115] Where, ν cutoff It is the highest infrared optical longitudinal mode frequency, ν cutoff =333 (cm) -1 );
[0116] ν i This refers to the central vibration frequency of each oscillator in a temperature-dependent single-phonon model.
[0117] ν i (T)=ν i (T0)+a1 i ·(T-T0)+a2 i ·(T-T0) 2 .
[0118] Δε iThis refers to the vibration intensity corresponding to each oscillator, which is temperature-dependent.
[0119] Δε i (T)=Δε i (T0)+b1 i ·(T-T0)+b2 i ·(T-T0) 2 .
[0120] Among them, Γ i The long-wavelength optical transverse mode frequency ν i The corresponding linewidth temperature-dependent linewidth expression is:
[0121]
[0122] Among them, a1 i b1 i c1 i c2 i These are the parameters for the single-phonon vibration model; please refer to Table 2 for their values.
[0123] Table 2
[0124]
[0125] In a preferred embodiment, the calculation process for the theoretical transmittance of the infrared material to each wavelength within the spectral band at a preset temperature includes:
[0126] The multiphonon absorption coefficient of the infrared material for the wavelength is calculated using the multiphonon absorption model; the single-phonon absorption coefficient of the infrared material for the wavelength is calculated using the single-phonon absorption model.
[0127] The theoretical absorption coefficient of the infrared material for the wavelength is obtained by summing the single-phonon absorption coefficient and the multiphonon absorption coefficient.
[0128] The multiphonon refractive index of the infrared material to the wavelength is calculated using the multiphonon refractive index model; the single phonon refractive index of the infrared material to the wavelength is calculated using the single phonon refractive index model.
[0129] The theoretical refractive index of the infrared material for the wavelength is obtained by summing the multiphonon refractive index and the singlephonon refractive index.
[0130] Based on the theoretical absorption coefficient and theoretical refractive index, the theoretical transmittance is obtained through Fresnel's law and the theory of light transmission.
[0131] Specifically, the expression for the theoretical absorption coefficient is: β(ν,T)=β onephonon (ν,T)+β multiphonon (ν,T).
[0132] Specifically, the theoretical refractive index is expressed as: n(ν,T)=n osc (v,T)+n multiphonon (ν,T).
[0133] Specifically, the unit of ν is cm. -1 Therefore, the wavelength range of 2-16μm corresponds to 5000-625cm. -1 The wavenumber range is given by ν being 5000-625 cm⁻¹. -1 Inside, every 1cm -1 A single value is selected, and a calculation is performed using the multiphonon absorption coefficient model at each wavenumber ν, completing the range from 5000 to 625 cm⁻¹. -1 After substituting all wavenumbers within the range, the ZnS multiphonon absorption coefficients at 300℃ for each wavelength in the spectral range of 2-16 μm can be obtained, such as... Figure 1 As shown.
[0134] Furthermore, calculations were performed at each wavenumber ν using the single-phonon absorption coefficient model, completing the calculations for 5000–625 cm⁻¹. -1 After substituting all wavenumbers within the range, the ZnS single-phonon absorption coefficients at 300℃ for each wavelength in the spectral range of 2-16 μm can be obtained, such as... Figure 3 As shown.
[0135] Furthermore, based on the expression for the theoretical absorption coefficient, the theoretical absorption coefficients of ZnS material at 300℃ for each wavelength in the spectral range of 2-16 μm were calculated, such as... Figure 5 As shown.
[0136] Specifically, let ν be between 5000-625cm -1 Inside, every 1cm -1 Perform one value selection, and then perform one calculation using the multiphonon refractive index model at each wavenumber ν to complete the 5000-625cm range. -1 After substituting all wavenumbers within the range, the multiphonon refractive index of ZnS at 300℃ for each wavelength in the spectral range of 2-16μm can be obtained, such as... Figure 2 As shown.
[0137] Furthermore, a calculation was performed at each wavenumber ν using the single-phonon refractive index model to complete the calculation for 5000-625 cm⁻¹. -1 After substituting all wavenumbers within the range, the ZnS single-phonon refractive index at 300℃ for each wavelength in the spectral range of 2-16 μm can be obtained, such as... Figure 4 As shown.
[0138] Furthermore, based on the expression for the theoretical refractive index, the theoretical refractive index of ZnS material at 300℃ for each wavelength in the spectral range of 2-16 μm was calculated, such as... Figure 6 As shown.
[0139] In a preferred embodiment, the calculation process of the theoretical transmittance includes:
[0140] The extinction coefficient is calculated based on the theoretical absorption coefficient.
[0141] Calculate the complex refractive index based on the extinction coefficient and the actual refractive index;
[0142] The first reflectance of light incident from air onto the surface of the infrared material is calculated based on the complex refractive index, and then the first transmittance is calculated. The second reflectance of light exiting from the surface of the infrared material onto air is calculated, and then the second transmittance is calculated.
[0143] The internal transmittance is calculated based on the thickness of the infrared material and the theoretical absorption coefficient.
[0144] The theoretical transmittance is calculated based on the first transmittance, the second transmittance, and the internal transmittance.
[0145] Specifically, the expression for the extinction coefficient is: k = βλ / 4π.
[0146] Where λ is the wavelength and π is the ratio of π to π.
[0147] Specifically, according to Snell's law: the complex refraction angle within a ZnS material satisfy
[0148] Where, N A Let N0 be the complex refractive index of ZnS material, N0 be the complex refractive index of air, and θ0 be the incident angle of light.
[0149] Where N0 = 1, N A =n+ik,
[0150] Furthermore, in this embodiment, θ0 is set to 0. According to Fresnel's law, the first reflectivity is obtained as follows:
[0151]
[0152] Second reflectivity:
[0153]
[0154] Furthermore, we obtain the first transmittance: T1 = 1 - R1, and the second transmittance: T2 = 1 - R2.
[0155] Specifically, based on the theory of light transmission, the expression for the internal transmittance of ZnS material is as follows:
[0156] u = exp(-βd);
[0157] Where d is the thickness of ZnS.
[0158] Furthermore, the expression for the theoretical transmittance is obtained as follows:
[0159] Furthermore, a calculation is performed at each wavenumber ν using the expression for the theoretical transmittance, completing the range from 5000 to 625 cm. -1 After substituting all wavenumbers within the range, the theoretical transmittance of ZnS at 300℃ for each wavelength in the spectral range of 2-16μm can be obtained, such as... Figure 7 As shown in curve 1
[0160] In a preferred embodiment, the actual optical constants include the actual absorption coefficient and actual refractive index of the infrared material for the wavelength.
[0161] In a preferred embodiment, the numerical optimization method is a particle swarm optimization algorithm or a genetic algorithm.
[0162] In a preferred embodiment, such as Figure 9 As shown, the steps of the particle swarm optimization algorithm include:
[0163] Initialize the particle swarm and parameter settings;
[0164] Calculate the objective function value;
[0165] Update individual optimal values and group optimal values;
[0166] Determine if the convergence data is satisfied; if so, output the optimal result and the number of iterations; otherwise, update the position vector and velocity vector of each particle and repeat the iteration process.
[0167] Specifically, in the Particle Swarm Optimization (PSO) algorithm, each solution to the optimization problem is represented by a bird in the search space, called a "particle." Each particle has a fitness value determined by an optimized function, and each particle also has a velocity that determines its direction and distance of flight. The particles then follow the current best particle in the solution space.
[0168] Specifically, the system initializes with a swarm of random particles (random solutions), and then iterates to find the optimal solution. In each iteration, a particle updates itself by tracking two "extremes." The first is the optimal solution found by the particle itself, called the individual extreme value. The other extreme value is the optimal solution found by the entire swarm so far, which is the global extreme value. Alternatively, instead of the entire swarm, only a subset of the particles can be used as their neighbors; in this case, the extreme value among all neighbors is the local extreme value.
[0169] Specifically, in this embodiment, the number of iterations is used as the termination criterion, the number of iterations is set to 20, and the population size is set to 50.
[0170] Specifically, the parameters D, K, α, and α in the optical constant calculation model are... (a / o)11 α (a / o)12 α (a / o)13 α (a / o)21 α (a / o)22 α (a / o)23 α3 was iteratively optimized near the theoretical value to obtain the optimized parameters. The optimization range and optimal results of each parameter are shown in Table 3.
[0171] Table 3
[0172]
[0173] Furthermore, the optimized parameters are input into the optical constant calculation model to obtain an optimized optical constant calculation model.
[0174] Furthermore, let ν be between 5000-625cm -1 Inside, every 1cm -1 A value is selected once, and a calculation is performed at each wavenumber ν using the optimized optical constant calculation model to complete the 5000-625cm range. -1 After substituting all wavenumbers within the range into the calculation, the optimized optical constants of ZnS at 300℃ for each wavelength in the spectral range of 2-16μm can be obtained, and then the optimized transmittance after optimizing the parameters can be calculated.
[0175] Specifically, the optimized optical constants include optimized refractive index and optimized extinction coefficient, such as... Figure 8 As shown, Figure 8 Curve 11 represents the optimized refractive index, and curve 22 represents the optimized transmittance. The optimized transmittance, as... Figure 7 As shown in curve 3, from Figure 7 As can be seen, the optimized transmittance is closer to the actual transmittance than the theoretical transmittance. Therefore, the optical constant calculation model is more practical, and its empirical parameters, after optimization, make the calculation accuracy of the optical constant higher.
[0176] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.
Claims
1. A method for inverting and calculating the high-temperature broadband optical constants of infrared materials, characterized in that, include: Select infrared materials and determine the spectral range for inversion calculation; At a preset temperature, the actual transmittance of the infrared material to each wavelength in the spectral range is tested using a spectrometer. Based on phonon absorption theory and Kramers–Krönig transform, an optical constant calculation model for the infrared material is established. The optical constant calculation model includes multiple model parameters, which are temperature-dependent. The theoretical transmittance of the infrared material to each wavelength in the spectral range at the preset temperature is calculated using the optical constant calculation model. With the goal of reducing the error between the theoretical transmittance and the actual transmittance, the model parameters are iteratively optimized within a predetermined range using a numerical optimization method to obtain optimized parameters. The optimized parameters are then substituted into the optical constant calculation model to calculate the actual optical constants of the infrared material. The optical constant calculation model includes: a multiphonon absorption coefficient model, a multiphonon refractive index model, a single-phonon absorption coefficient model, and a single-phonon refractive index model; The calculation process for the theoretical transmittance of the infrared material to each wavelength within the spectral range at a preset temperature includes: The multiphonon absorption coefficient of the infrared material for the wavelength is calculated using the multiphonon absorption model; the single-phonon absorption coefficient of the infrared material for the wavelength is calculated using the single-phonon absorption model. The theoretical absorption coefficient of the infrared material for the wavelength is obtained by summing the single-phonon absorption coefficient and the multiphonon absorption coefficient. The multiphonon refractive index of the infrared material to the wavelength is calculated using the multiphonon refractive index model; the single phonon refractive index of the infrared material to the wavelength is calculated using the single phonon refractive index model. The theoretical refractive index of the infrared material for the wavelength is obtained by summing the multiphonon refractive index and the singlephonon refractive index. Based on the theoretical absorption coefficient and theoretical refractive index, the theoretical transmittance is obtained through Fresnel's law and the theory of light transmission. The establishment of the multiphonon absorption coefficient model includes: Establish n phonon state intensity function S n ( ν, T ); Establish n phonon density of states function ρ n ( ν, T ); Based on the above S n ( ν, T ) and the ρ n ( ν, T The multiphonon absorption coefficient model is established based on multiphonon absorption theory. ; in, ν Where T is the wave number and T is the temperature; The establishment of the multiphonon refractive index model includes: The n phonon density of states function ρ n ( ν, T Performing the Kramers–Krönig transform yields δ n ( ν ); Based on the above n phonon state intensity function S n ( ν, T )and δ n ( ν ), thus obtaining the multiphonon refractive index model. , in, δ n ( ν () is the result after Kramers–Krönig transformation n phonon state density function; ν max The maximum longitudinal vibration frequency of the crystal lattice. Pi T 0 represents room temperature; α (a / o)11 , α (a / o)12 , α (a / o)13 All are empirical parameters that include phonon information from both optical and acoustic modes. for n The frequencies associated with optical and acoustic modes in the intensity function of the first phonon state.
2. The method for inverting and calculating the high-temperature broadband optical constants of infrared materials according to claim 1, characterized in that, Dielectric function obtained based on single-phonon oscillator model ε r Based on the dielectric function ε r Establish the single-phonon absorption coefficient model Based on the dielectric function ε r Establish the single-phonon refractive index model .
3. The method for inverting and calculating the high-temperature broadband optical constants of infrared materials according to claim 1, characterized in that, The calculation process for the theoretical transmittance includes: The extinction coefficient is calculated based on the theoretical absorption coefficient. Calculate the complex refractive index based on the extinction coefficient and the actual refractive index; The first reflectance of light incident from air onto the surface of the infrared material is calculated based on the complex refractive index, and then the first transmittance is calculated. The second reflectance of light exiting from the surface of the infrared material onto air is calculated, and then the second transmittance is calculated. The internal transmittance is calculated based on the thickness of the infrared material and the theoretical absorption coefficient. The theoretical transmittance is calculated based on the first transmittance, the second transmittance, and the internal transmittance.
4. The method for inverting and calculating the high-temperature broadband optical constants of infrared materials according to claim 1, characterized in that, The actual optical constants include the actual absorption coefficient and actual refractive index of the infrared material for the wavelength.
5. The method for inverting and calculating the high-temperature broadband optical constants of infrared materials according to claim 1, characterized in that, The numerical optimization method selected is either particle swarm optimization or genetic algorithm.
6. The method for inverting and calculating the high-temperature broadband optical constants of infrared materials according to claim 5, characterized in that, The steps of the particle swarm optimization algorithm include: Initialize the particle swarm and parameter settings; Calculate the objective function value; Update individual optimal values and group optimal values; Determine if the convergence data is satisfied; if so, output the optimal result and the number of iterations; otherwise, update the position vector and velocity vector of each particle and repeat the iteration process.