CN102944519A - Optical system and method for measuring thermal physical property parameters of solid - Google Patents

Abstract

The invention provides an optical system and method for measuring the thermophysical parameters of a solid. The optical system includes: a heating laser generating component, a probing laser generating component, a beam combining element, a light splitting element, a heating laser receiving component, a sample testing component and a probing laser receiving component. The invention adopts signal-modulated photothermal reflection method, which belongs to frequency domain method. Compared with time domain methods such as ultrashort pulse laser pumping detection method, it has no mechanical moving parts, relatively simple measurement system and more convenient optical path adjustment.

Description

Optical system and method for measuring thermal and physical parameters of solid

technical field

The invention relates to a photothermal reflection measurement technology using periodic modulation heating and continuous laser detection, in particular to an optical system and method for measuring solid thermophysical parameters.

Background technique

Thin film materials have been widely used in microelectronics, optoelectronics, micromanufacturing and other fields, and these micro/nano devices will generate extremely high heat flux density during operation, and heat accumulation will directly affect the working efficiency and reliability of such devices. It is extremely urgent to solve the heat dissipation problem of the above-mentioned micro/nano devices, which requires accurate characterization of the thermophysical properties of the thin film materials that make up the above-mentioned micro/nano devices, especially the thermal conductivity and interface thermal resistance, in order to reveal the heat transport mechanism. The 3ω method is a commonly used method for measuring thermal physical properties of thin film materials, but it needs to weld metal sheets/wires on the sample to be tested, which belongs to the destructive testing technology.

The ultrashort pulse laser pumping detection method is a new method for measuring the thermophysical parameters of solids. Fig. 1 is a schematic diagram of an optical path of an optical system for measuring thermophysical parameters of a solid in the prior art. As shown in Figure 1, the optical system includes: a laser 1 outputs pulsed laser light; the first wave plate 2 (half wave plate) rotates the polarization direction of the laser light; the first beam splitter 3 divides the laser beam into Two beams; the electro-optic modulator 4 modulates the laser beam; the electro-optic modulator driver 5 sends modulation signals to the electro-optic modulator 4; the first mirror 6 receives and reflects the laser beam; the laser beam passes through the first focusing lens 7 and the frequency doubling crystal 8 And the second focusing lens 9, produces the second harmonic; the first optical filter 10 filters incoherent light; the beam expander 11 expands the diameter of the laser beam; the second mirror 12 receives and reflects the laser beam; the electric control displacement platform 14 Move back and forth; the laser beam passes through the second wave plate 15 (half wave plate) after being reflected by the parallel light reflector 13, and the laser polarization direction rotates; the second beam splitter 16 divides the laser beam into two beams whose polarization directions are perpendicular to each other; The laser beam passes through the third wave plate 17 (quarter wave plate) and is vertically incident on the surface of the sample, and returns to the original path and passes through the third wave plate 17 again to realize a 90-degree change in the polarization direction; the cold mirror 18 converts the laser beams of different wavelengths Combining beams; focusing lens 19 irradiates the laser light on the sample surface on the fixed adjustment frame 20; electro-optic detector 23 receives the laser beam passing through the second optical filter 21 and the third focusing lens 22; the signal output of electro-optic detector 23 to filter amplifier 24. Femtosecond pulsed lasers with different wavelengths are used for the pumping light and the probe light, which are combined into a laser beam through a cold mirror. Before the pumping light and the probe light reach the detector, a filter with high selectivity is used to filter out frequency multiplication The final pumping light avoids the interference of the pumping light on the signal and realizes accurate and efficient measurement; the filter amplifier can effectively filter out the influence of high-frequency harmonics and effectively improve the accuracy of the signal.

Different moving distances of the electronically controlled displacement platform correspond to different delay times between the probe light and the pumping light. The output signal of the filter amplifier is compared with the modulation signal given by the electro-optic modulator driver to obtain a phase difference signal. The phase difference signal is measured data obtained from experiments.

However, for the optical path system for measuring the thermophysical parameters of solids shown in Figure 1, the electronically controlled displacement platform is a mechanical moving part, and it is difficult to control it precisely; it is composed of a first focusing lens, a frequency doubling crystal and a second focusing lens The frequency doubling module is difficult to collinearly focus and the efficiency of frequency doubling is not high.

Contents of the invention

(1) Technical problems to be solved

In order to solve one or more of the above problems, the present invention provides an optical system and method for measuring thermal and physical parameters of solids with precise control and convenient adjustment.

(2) Technical solutions

According to one aspect of the present invention, an optical system for measuring thermal and physical parameters of a solid is provided. The system includes: heating laser generating components, probing laser generating components, beam combining elements, beam splitting elements, heating laser receiving components, sample testing components and probing laser receiving components; wherein, the heating laser generating components generate frequency-modulated continuous polarization heating The laser beam is continuously polarized detection laser light generated by the detection laser generating component; the heating laser and the detection laser beam are combined into a beam combining laser located on the A plane after passing through the beam combining element; the beam combining laser is incident on the beam splitting element, and the polarization direction is in the The component is transmitted to the sample test component, and the component whose polarization direction is perpendicular to the horizontal plane is reflected to the heating laser receiving component; the combined beam component with the polarization direction in the A plane passes through the sample test component and irradiates the surface of the tested sample; the polarization direction is in the A plane The heating laser in the combined beam component heats the tested sample, and the heated tested sample modulates the detection laser; After testing the component, it is reflected by the light splitting element to the detection laser receiving component; the detection laser receiving component filters the heating laser component in the incident beam combination laser to obtain the signal of the detection laser; the heating laser receiving component converts the detection laser in the incident beam combination laser After the component is filtered out, the signal of the heating laser is obtained.

According to another aspect of the present invention, there is also provided a method for measuring the thermophysical parameters of a solid by using the above-mentioned optical system, including: step A, using the optical system to obtain different heating laser modulation frequencies, and using the detection laser receiving component to generate detection The laser signal and the heating laser signal generated by the heating laser receiving component, both the detection laser signal and the heating laser signal contain power information and phase information; step B, under different heating laser modulation frequencies, the detection laser signal and the heating laser signal Perform phase difference processing to obtain the experimental value of the phase difference; step C, assign initial values to the thermal physical parameters of the solid to be fitted; step D, under different heating laser modulation frequencies, according to the theoretical model formula, calculate the experimental value of the phase difference The theoretical value of the phase difference at the corresponding frequency; step E, the least square calculation is performed on the experimental value of the phase difference at all heating laser modulation frequencies and the corresponding theoretical value of the phase difference, and the least square calculation value is used as the current iteration result; step F, record the thermal conductivity value and interface thermal conductivity value corresponding to the current iteration result; Step G, judge whether the result of this iteration is smaller than the result of the previous iteration, if yes, perform step H, otherwise, perform step I; step H , using the solid thermophysical parameter value corresponding to the result of this iteration as the change detection output data, and performing step J; step I, using the solid thermophysical property parameter value corresponding to the previous iteration result as the change detection output data, performing step J; step J , judging whether the result of three consecutive iterations is less than the control accuracy, if yes, execute step K, otherwise, execute step L; step K, stop the iteration, output the solid thermophysical property parameter value obtained by step H or step I, and the process ends; Step L, increase or decrease the thermophysical parameter value of the solid obtained by step H or step I according to the preset step size, determine the value change path by the preset optimization function, and execute step D.

(3) Beneficial effects

It can be seen from the above-mentioned technical scheme that the optical system and method for measuring the thermal and physical parameters of solids in the present invention have the following beneficial effects: the photothermal reflection method using signal modulation belongs to the frequency domain method, and the ultrashort pulse laser pumping detection method is equivalent Compared with the field method, there are no mechanical moving parts, the measurement system is relatively simple, and the optical path adjustment is more convenient.

Description of drawings

Fig. 1 is the optical path schematic diagram of the optical system of measuring solid thermophysical property parameter in the prior art;

2 is a schematic diagram of an optical path of an optical system for measuring thermal and physical parameters of a solid according to an embodiment of the present invention;

Fig. 3 is a flow chart of a method for measuring thermophysical parameters of a solid according to an embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

It should be noted that, in the drawings or descriptions of the specification, similar or identical parts all use the same figure numbers. Implementations not shown or described in the accompanying drawings are forms known to those of ordinary skill in the art. Additionally, while illustrations of parameters including particular values may be provided herein, it should be understood that the parameters need not be exactly equal to the corresponding values, but rather may approximate the corresponding values within acceptable error margins or design constraints. In addition, the directional terms mentioned in the following embodiments, such as "upper", "lower", "front", "rear", "left", "right", etc., are only referring to the directions of the drawings. Accordingly, the directional terms are used to illustrate and not to limit the invention.

As for FIG. 1 , it is a drawing of an optical system for measuring solid thermophysical properties in the prior art, and the figure numbers marked in the figure are for reference only, and are not included in the present invention. For the convenience of those skilled in the art to understand the present invention, firstly, the main elements involved in the present invention are numbered and described, specifically as follows:

10-heating laser components; 20-detection laser components;

30-beam combining element; 40-light splitting element;

50-heating laser receiving component; 60-sample testing component;

70-sample fixing element; 80-detection laser receiving component;

11-signal modulator; 12-first laser;

13-the first wave plate; 14-the first reflector;

21-the second laser; 22-the second wave plate;

23-the second reflector; 51-the first optical filter;

52-the first photodetector; 61-the third wave plate;

62-objective lens; 81-focusing lens;

82-the second optical filter; 83-the second photodetector.

In an exemplary embodiment of the present invention, an optical system for measuring thermophysical parameters of a solid is provided. As shown in Figure 2, the system includes: a heating laser generating assembly 10, a probing laser generating assembly 20, a beam combining element 30, a light splitting element 40, a heating laser receiving assembly 50, a sample testing assembly 60, a sample fixing element 70, a probing laser receiving assembly Component 80 and data processing components (not shown). The frequency-modulated continuously polarized heating laser is generated by the heating laser generating component 10, and the continuously polarized detecting laser is generated by the probing laser generating component 20; the heating laser and the probing laser are combined into a beam combining laser located on the horizontal plane after passing through the beam combining element 30 The combined beam laser is incident on the light splitting element 40, and the component with the polarization direction in the horizontal plane is transmitted to the sample test assembly 60, and the component with the polarization direction perpendicular to the horizontal plane is reflected to the heating laser receiving component 50; the combined beam light component with the polarization direction in the horizontal plane After passing through the sample testing assembly 60, it is irradiated onto the surface of the tested sample on the sample fixing element 70, the heating laser heats the tested sample, and the heated tested sample produces a modulation effect on the detection laser; the tested sample on the sample fixing element 70 The combined laser beam of the heating laser reflected on the sample surface and the modulated probing laser passes through the sample test component 60 and is reflected by the spectroscopic element 40 to the probing laser receiving component 80; the probing laser receiving component 80 converts the incident heating laser and probing laser After the heating laser component is filtered out, the signal of the detection laser is obtained; after the heating laser receiving component 50 filters out the detection laser component in the incident heating laser and detection laser, the signal of the heating laser is obtained; the data processing component is determined by the modulation frequency of the heating laser , The detection laser receiving component 50 generates the detection laser signal and the heating laser receiving component 80 generates the signal of the heating laser, and the thermophysical parameters of the sample to be tested are obtained by reverse deduction according to the theoretical model.

Each component/element will be described in detail below.

Heating the laser generating assembly 10

The heating laser generating component 10 is used to generate a signal-modulated continuous polarized heating laser. As shown in Figure 1, the heating laser generating assembly includes: a signal modulator 11, which can be a digital signal generator, used to modulate the first laser, its modulation frequency is controlled by an external computer, and the modulation frequency range is determined by the signal modulator 11 and the data The processing components are jointly determined, which can be 50kHz to 20MHz; the first laser 12 is a semiconductor laser, which is used to output a continuous polarized laser with a wavelength of 830nm under the modulation of the signal modulator 11, and its power is 170mW; the first wave plate 13 , is a half-wave plate, used to adjust the ratio of the horizontally polarized component and the vertically polarized component of the continuous polarized laser output from the first laser 12; the first laser reflector 14, whose reflectivity is greater than 99%, and whose reflective surface is the same as The heating laser beam passing through the first wave plate 13 is at an angle of 45°, and is used to deflect the incident adding laser light by 90°, and then enter the beam combining element 30 at an angle of 45°.

Probe laser generating assembly 20

The probing laser generating component 20 is used to generate continuously polarized probing laser. The wavelength of the probing laser is different from that of the heating laser, and the power is much smaller than that of the heating laser. As shown in Figure 1, the heating laser generating assembly 20 includes: a second laser 21, which is a semiconductor laser, used to output a probe laser with a wavelength of 635nm, and its power is 6mW; the second wave plate 22 is a half wave plate , for adjusting the ratio of the horizontally polarized component and the vertically polarized component of the continuous polarized laser output by the second laser 21; The detection laser is at an angle of 45°, and is used for deflecting the incident detection laser light by 90°, and entering the beam combining element 30 at an angle of 45°.

beam combining element 30

The beam-combining element 30 is a cold mirror, which completely transmits the heating laser light with a wavelength of 830nm incident at an angle of 45° to its plane; it totally reflects the detection laser light with a wavelength of 635nm incident at an angle of 45° to its plane, so that the heating laser and the detection Laser beam combining to achieve collinear heating detection.

Light splitting element 40

The spectroscopic element 40 is a spectroscopic prism. Through the beam splitting prism, among the combined heating laser and probe laser, the component whose polarization direction is on the horizontal plane is transmitted to the sample testing component, and the component whose polarization direction is perpendicular to the horizontal plane is reflected to the heating laser receiving component; the heating reflected by the sample surface The laser light and the detection laser light are reflected to the detection laser receiving component.

Heating the laser receiving assembly 50

The heating laser receiving component 50 is configured to obtain a signal of the heating laser after filtering out the detection laser component in the incident heating laser and the detection laser. The heating laser receiving component 50 includes: a first filter 51 and a first photodetector 52 . in:

The first optical filter 51 is used to filter out the detection laser component in the incident combined laser beam, and its transmittance for the detection laser light with a wavelength of 635nm is 10 ⁻⁷ to 10 ⁻⁹ .

The first photodetector 52 is used to detect the signal of the heating laser in the combined laser beam, which can be a high-speed PIN diode, an avalanche diode, a photomultiplier tube, or a charge-coupled device, and the response time is less than 10 ns. Wherein, the signal may include information such as power (amplitude), phase, and the like.

Sample Test Kit 60

The combined laser beam of the heating laser and the probing laser transmitted through the spectroscopic element 40 passes through the sample testing component 60 and interacts with the surface of the sample to be tested on the sample fixing component, and the heating laser and probing laser reflected by the sample surface re-enter through the sample testing component 60 to the light splitting element 40 .

The sample testing assembly 60 includes: a quarter wave plate 61 and an objective lens 62 . Wherein the objective lens 62 is an achromatic objective lens with a magnification of 100 times and a focal length of 2mm. After the incident combined laser beam passes through the quarter-wave plate 61 twice, its polarization direction changes by 90°.

Sample Fixture 70

The sample fixing element 70 is a fixed adjustment frame, which is used to adjust and fix the orientation of the sample to be tested, so as to ensure that the combined beam laser is perpendicular to the surface of the tested sample, and the reflected beam combined laser returns to the original path and is incident on the sample testing component 60 .

The heating laser heats the test sample, and the heated test sample modulates the detection laser light; the combined laser beam of the heating laser reflected by the surface of the test sample on the sample fixing element 70 and the modulated detection laser passes through the sample test again. The component 60 is then reflected by the light splitting element 40 to the detection laser receiving component 80 .

Probe laser receiver assembly 80

The detection laser receiving component 80 is used to obtain a signal of the detection laser after filtering the incident heating laser and the heating laser component in the detection laser. The detection laser receiving component 80 includes: a focusing lens 81 , a second filter 82 and a second photodetector 83 . in:

The focusing lens 81 is used to focus the incident combined laser beams. According to different requirements, the focal length of the focusing lens 81 can be 10 mm to 300 mm.

The second optical filter 82 is used to filter out the heating laser component in the focused combined laser beam, and its transmittance for the heating laser with a wavelength of 830nm is 10 ⁻⁷ to 10 ⁻⁹ .

The second photodetector 83 is used to detect the signal of the detection laser in the combination laser, which can be a high-speed PIN diode, an avalanche diode, a photomultiplier tube, or a charge-coupled device, and the response time is less than 10 ns. Wherein, the signal may include information such as power (amplitude), phase, and the like.

Using the signals obtained by the above-mentioned heating laser receiving component and probing laser receiving component, the thermophysical parameters of the solid can be calculated and obtained. Compared with time-domain methods such as ultra-short pulse laser pumping detection method, the optical system for measuring the thermophysical parameters of the solid has no mechanical moving parts, the measurement system is relatively simple, and the optical path adjustment is more convenient.

Based on the above-mentioned optical system, the present invention also provides a method for measuring the thermophysical parameters of a solid. The method is based on the detection laser signal generated by the detection laser receiving component and the heating generated by the heating laser receiving component under different angular frequencies of the signal modulator. The phase difference of the laser signal is fitted to obtain the thermophysical parameters of the tested sample, including thermal conductivity and interface thermal conductivity between materials.

In an exemplary embodiment of the present invention, as shown in Figure 3, the method includes:

Step A, using the above-mentioned optical system to obtain the detection laser signal generated by the detection laser receiving component and the signal of the heating laser generated by the heating laser receiving component under different heating laser modulation frequencies, the detection laser signal and the heating laser signal both contain power information and phase information;

Step B, performing phase difference processing on the detection laser signal and the heating laser signal under different heating laser modulation frequencies to obtain the experimental value of the phase difference;

Step C, assigning initial values to the thermal conductivity to be fitted and the interface thermal conductance;

Step D, at different heating laser modulation frequencies, according to the theoretical model formula, calculate the theoretical value of the phase difference at the frequency corresponding to the experimental value of the phase difference;

$\mathrm{<span\; class="notranslate">\; Z</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="Q"\; filenames="HDA00002436580400021.png"\; state="\{\{state\}\}">Q</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{<span\; class="notranslate">\; \&infin;</span>}\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; D.</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span>\frac{<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; l</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="HDA00002436580400021.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 8</span>}}<span\; class="notranslate">\; ]</span>\mathrm{<span\; class="notranslate">\; dl</span>}$

$\mathrm{<span\; class="notranslate">\; \&phi;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; arctan</span>}<span\; class="notranslate">\; \{</span>\frac{\mathrm{<span\; class="notranslate">\; Im</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; Z</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}{\mathrm{<span\; class="notranslate">\; Re</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; Z</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}<span\; class="notranslate">\; \}</span>$

Among them, Q ₀ and Q ₁ are the power of the heating laser and the detection laser respectively, γ is the light reflection coefficient of the surface of the tested sample, l is the integral variable, R ₀ and R ₁ are the beam waists when the heating laser and the detection laser are generated, respectively Radius, ω is the angular frequency of the modulation signal; φ is the theoretical value of the phase difference between the detection laser received by the detection laser receiving component and the heating laser received by the heating laser receiving component. C and D are 2×2 material thermophysical parameter matrix $\left[\begin{array}{cc}A& B\\ C& \mathrm{D.}\end{array}\right]$ The corresponding parameters for :

$\left[\begin{array}{cc}\mathrm{<span\; class="notranslate">\; A</span>}& \mathrm{<span\; class="notranslate">\; B</span>}\\ \mathrm{<span\; class="notranslate">\; C</span>}& \mathrm{<span\; class="notranslate">\; D.</span>}\end{array}\right]<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="m"\; filenames="HDA00002436580400021.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}$

If it is a certain layer, $m_j={\left[\begin{array}{cc}\cosh \left(\mathrm{qd}\right)& -k^{-1}{q}^{-1}\sinh \left(\mathrm{qd}\right)\\ -\mathrm{kq}\sinh \left(\mathrm{qd}\right)& \cosh \left(\mathrm{qd}\right)\end{array}\right]}_j$

If it is an interface, $m_j={\left[\begin{array}{cc}1& -G^{-1}\\ 0& 1\end{array}\right]}_j$

ρ、c、k、d分别为某层的密度、质量热容、热导率、厚度，G为界面热导，i为虚数单位，j为从激光入射端算起的层数。in,

ρ, c, k, and d are the density, mass heat capacity, thermal conductivity, and thickness of a certain layer, respectively, G is the interface thermal conductivity, i is the imaginary number unit, and j is the number of layers counted from the laser incident end.

In addition, for the specific meaning of the thermal physical parameters of the above materials, please refer to Reference 1 [J.Zhu et al.J.Appl.Phys.108, 094315(2010))].

Step E, performing a least squares calculation on the phase difference experimental values at all heating laser modulation frequencies and the corresponding phase difference theoretical value, and the least squares calculated value as the result of the current iteration;

Step F, record the thermal conductivity value and interface thermal conductivity value corresponding to the current iteration result, which is the current optimal data;

Step G, judging whether the result of this iteration is smaller than the result of the previous iteration, if yes, execute step H, otherwise, execute step I;

Step H, use the thermal conductivity value and interface thermal conductivity value corresponding to the iterative result as the change detection output data, and execute step J;

Step I, use the thermal conductivity value and interface thermal conductivity value corresponding to the previous iteration result as the change detection output data, and execute step J;

Step J, judging whether the result of three consecutive iterations is less than the control precision (such as 10 ^-6 ), if yes, execute step K, otherwise, execute step L;

Step K, stop the iteration, output the thermal conductivity value and the interface thermal conductivity value obtained by step H or step I, and the process ends;

Step L, increase or decrease the thermal conductivity value and interface thermal conductivity value obtained in step H or step I according to the preset step size, determine the value change path by the preset optimization function, and execute step D.

In this step, the preset step size can be 0.5-5% of the current thermal conductivity value and the interface thermal conductivity value; the optimization function can be lsqcurvefit function, fminsearch function or other functions known in the art.

It should be noted that the above two-parameter fitting method obtains the thermal conductivity value and the interface thermal conductivity value at the same time. Of course, on the premise that one of the above-mentioned values is determined to be a fixed value, the single-parameter fitting method can also be used. Get another specific value. According to the above description, those skilled in the art can easily think of related calculation methods, which will not be repeated here.

It should be noted that the above definition of each element is not limited to the various specific structures or shapes mentioned in the embodiment, and those skilled in the art can simply replace them with familiar ones, for example:

(1) The heating laser or detection laser can also enter the laser reflector at other angles;

(2) The optical path of the system may not be on the horizontal plane, and the horizontal plane is selected in the embodiment just for the convenience of adjustment;

(3) The focusing lens only plays the role of concentrating the light beam and incident it into the photosensitive area of the photodetector. In the heating laser receiving component, adding or removing the focusing lens will not affect the measurement results;

(4) The first and second photodetectors may be high-speed PIN diodes, avalanche diodes, photomultiplier tubes, or charge-coupled devices.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (14)

1. An optical system for measuring a thermophysical parameter of a solid, comprising: the device comprises a heating laser generating assembly, a detection laser generating assembly, a beam combining element, a light splitting element, a heating laser receiving assembly, a sample testing assembly and a detection laser receiving assembly; wherein,

generating continuously polarized heating laser with frequency modulation by the heating laser generating assembly, and generating continuously polarized detection laser by the detection laser generating assembly; the heating laser and the detection laser are combined into a combined laser positioned on the plane A after passing through a beam combining element;

the beam-combined laser is incident to the light splitting element, the component with the polarization direction in the plane A is transmitted to the sample testing component, and the component with the polarization direction vertical to the horizontal plane is reflected to the heating laser receiving component; the beam combination light component with the polarization direction in the plane A is irradiated to the surface of the tested sample after passing through the sample testing assembly;

heating the detected sample by the heating laser in the beam combination optical component with the polarization direction in the plane A, and modulating the detection laser by the heated detected sample; the combined laser of the heating laser reflected by the surface of the tested sample and the modulated detection laser passes through the sample testing component again and then is reflected to the detection laser receiving component by the light splitting element;

the detection laser receiving assembly filters out heating laser components in the incident combined laser to obtain a detection laser signal; and the heating laser receiving assembly filters out detection laser components in the incident combined laser to obtain a signal of the heating laser.

2. The optical system of claim 1, wherein the beam combining element is a cold mirror;

the cold mirror is fully transmitted to the heating laser which is incident at an angle of 45 degrees with the plane where the cold mirror is located; and totally reflecting the incident detection laser forming an angle of 45 degrees with the plane where the laser is positioned, so that the combination of the heating laser and the detection laser is realized to be combined laser positioned on the plane A.

3. The optical system of claim 2, wherein the heated laser generating assembly comprises:

a signal modulator;

the first laser is a semiconductor laser and is used for outputting continuous polarized laser under the modulation of the signal modulator;

the first wave plate is a half wave plate and is used for adjusting the proportion of the horizontal polarization component and the vertical polarization component of the continuous polarization laser output by the first laser; and

and the reflecting surface of the first laser reflector forms a 45-degree angle with the heating laser which is transmitted through the first wave plate, and the first laser reflector is used for deflecting the incident added laser by 90 degrees and then irradiating the beam combining element at the 45-degree angle.

4. The optical system of claim 2, wherein the modulation frequency of the signal modulator is between 50kHz and 20 MHz.

5. The optical system of claim 2, wherein the probe laser generating assembly comprises:

the second laser is a semiconductor laser and is used for outputting continuously polarized detection laser;

the second wave plate is a half wave plate and is used for adjusting the proportion of the horizontal polarization component and the vertical polarization component of the continuous polarization laser output by the second laser; and

and the reflecting surface of the second laser reflector forms a 45-degree angle with the detection laser which is transmitted through the second wave plate, and the second laser reflector is used for deflecting the incident detection laser by 90 degrees and then irradiating the beam combination element at the 45-degree angle.

6. The optical system of claim 1, wherein the beam splitting element is a beam splitting prism.

7. The optical system of claim 1, wherein the sample testing assembly comprises:

a quarter-wave plate for changing the polarization direction of the combined laser beam passing through the quarter-wave plate by 45 degrees each time; and

and the objective lens is used for focusing the combined beam light component of the polarization direction of the quarter-wave plate on the plane A to the tested sample and re-transmitting the combined beam laser of the heating laser reflected by the surface of the tested sample and the modulated detection laser to the quarter-wave plate.

8. The optical system of claim 1, wherein the heated laser receiving assembly comprises:

the first optical filter is used for filtering detection laser components in the incident combined beam laser; and

a first photodetector for detecting a signal of the heating laser light in the combined laser light, wherein the signal includes: power and/or phase information.

9. The optical system of claim 1, wherein the detection laser receiving assembly comprises:

the second optical filter is used for filtering heating laser components in the incident combined beam laser; and

a second photodetector for detecting a signal of the detection laser in the combined laser, wherein the signal includes: power and/or phase information.

10. The optical system of claim 9, wherein the detection laser receiving assembly further comprises:

and the focusing mirror is positioned in front of the optical path of the second optical filter and used for focusing the incident combined laser, and the focused combined laser enters the second optical filter.

11. A method of measuring a thermophysical parameter of a solid using the optical system of any one of claims 1 to 10, comprising:

step A, acquiring a detection laser signal generated by a detection laser receiving assembly and a heating laser signal generated by a heating laser receiving assembly under different heating laser modulation frequencies by using the optical system, wherein the detection laser signal and the heating laser signal both contain power information and phase information;

b, performing phase difference processing on the detection laser signal and the heating laser signal under different heating laser modulation frequencies to obtain a phase difference experimental value;

step C, assigning an initial value to the thermophysical property parameter of the solid to be fitted;

step D, calculating a phase difference theoretical value under the frequency corresponding to the phase difference experimental value according to a theoretical model formula under different heating laser modulation frequencies;

step E, performing least square calculation on the phase difference experimental values and the corresponding phase difference theoretical values under all the heating laser modulation frequencies, wherein the least square calculation value is used as a current iteration result;

step F, recording a thermal conductivity value and an interface thermal conductivity value corresponding to the current iteration result;

g, judging whether the result of the current iteration is smaller than the result of the previous iteration, if so, executing the step H, otherwise, executing the step I;

step H, taking the solid thermophysical property parameter value corresponding to the iteration result as change detection output data, and executing step J;

step I, taking the solid thermophysical property parameter value corresponding to the previous iteration result as change detection output data, and executing step J;

step J, judging whether the iteration result of 3 times is less than the control precision, if so, executing the step K, otherwise, executing the step L;

step K, stopping iteration, outputting the solid thermophysical property parameter value obtained in the step H or the step I, and ending the process; and

and step L, increasing or decreasing the solid thermophysical property parameter value obtained in the step H or the step I according to a preset step length, determining a numerical value change path by a preset optimization function, and executing the step D.

12. The method of claim 11, wherein the theoretical model formula in step D is:

$Z\left(\mathrm{\&omega;}\right)=-\frac{\mathrm{\&gamma;}{Q}_0{Q}_1}{2\mathrm{\&pi;}}{\&Integral;}_0^{\&infin;}l\left(\frac{D}{C}\right)\exp \left[\frac{-l^2(R_0^2+R_1^2)}{8}\right]\mathrm{dl}$

$\mathrm{\&phi;}=\arctan \left\{\frac{\mathrm{Im}\left[Z\left(\mathrm{\&omega;}\right)\right]}{\mathrm{Re}\left[Z\left(\mathrm{\&omega;}\right)\right]}\right\}$

wherein Q is₀、Q₁Power of heating laser and detection laser, gamma is light reflection coefficient of tested sample surface, l is integral variable, R is₀、R₁The beam waist radii of the heating laser and the detection laser are respectively, Z represents a signal obtained by the data processing assembly, and omega is the angular frequency of a modulation signal; phi is the phase difference between the detection laser received by the detection laser receiving assembly and the heating laser received by the heating laser receiving assemblyTheoretical value, C, D is a 2 x 2 material thermophysical property parameter matrix $\left[\begin{array}{cc}A& B\\ C& D\end{array}\right]$ Of the corresponding parameter.

13. The method according to claim 11, wherein in the step L, the preset step length is 0.5-5% of the current solid thermophysical property parameter value; the optimization function is an lsqcurvefit function or an fmisearch function.

14. The method of any one of claims 11 to 13, wherein the solid thermophysical parameter is thermal conductivity, and/or interfacial thermal conductivity.

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