Frequency domain thermal reflection light spot offset thermal conductivity measuring method

Abstract

The invention discloses a frequency domain thermal reflection light spot offset thermal conductivity measurement method. According to the method, the offset of heating laser and detection laser is accurately controlled, a light spot position signal is collected by adopting a modulation frequency scanning technology, and the thermal conductivity of the high polymer material is accurately measured in combination with an isotropic free thermal expansion model and Hankel transformation analysis. The system integrates a laser source module, a light path regulation and control module, a signal acquisition module and a data processing module, and effectively avoids the problems of contact errors and heat insulation environment requirements in a traditional method through a non-contact measurement mode. Experiments show that the measurement accuracy of the method is remarkably improved especially for low-thermal-conductivity materials, the requirements for the sample size and flatness are low, and an efficient and reliable solution is provided for establishment of a high polymer material thermophysical property database.

Description

Technical Field

[0001] This invention relates to the field of nanoscale thermal conduction, and specifically to a method for measuring the thermal conductivity of frequency-domain thermal reflection spot shift. Background Technology

[0002] Polymer materials are compounds composed of hundreds or thousands of repeating units, with relative molecular masses ranging from several thousand to several million. Adjacent repeating units are generally connected by covalent bonds. Due to the different chemical compositions and arrangements of the repeating units, polymer materials exhibit a highly entangled, disordered, and complex structure. Macroscopically, this manifests in the following ways: In terms of mechanical properties, low intermolecular forces result in low strength and hardness, while the free movement and rearrangement of molecular chains lead to high elasticity and toughness; in terms of optical properties, the disordered arrangement of molecular chains causes significant light scattering, making the material opaque; in terms of electrical properties, the disordered internal arrangement and lack of free electron movement result in insulating properties, making it widely used in the field of electronic device insulation; in terms of thermal properties, the disordered arrangement, weak intermolecular forces, and lack of free electrons result in extremely low intrinsic thermal conductivity, only about 0.1 W / (mK); and in terms of processing properties, the disordered structure makes it easy to flow and form, allowing for the production of various shapes through injection molding, extrusion, and other processing methods.

[0003] Because of their excellent processing performance and electrical insulation properties, polymer materials have broad application prospects and are widely used in electronic devices such as chip heat dissipation and mobile phone back panels. However, due to their extremely low intrinsic thermal conductivity, they are gradually failing to meet industrial heat dissipation requirements. A common method to improve the overall thermal conductivity of materials is to composite them with high thermal conductivity materials, such as ceramic-based or metal-based fillers. When the filler ratio is low, this method can improve the overall thermal conductivity of the composite material as the filler content increases. According to the effective medium theory, the thermal conductivity of the composite material is greatly affected by the intrinsic thermal conductivity of the polymer material. However, if the filler ratio is too high, it can negatively impact processing performance, making the material difficult to mold, and the added filler may also affect insulation performance. If the intrinsic thermal conductivity of polymer materials can be increased to 1.0 W / (m K) or higher, both the polymer material itself and the polymer composite material will better meet the heat dissipation requirements of modern industrial high-speed integrated electronic devices, significantly enhancing industry competitiveness.

[0004] Due to the structural complexity of polymer materials, it is difficult to obtain an accurate theoretical formula for intrinsic thermal conductivity. In order to improve the intrinsic thermal conductivity of polymer materials, it is first necessary to obtain the structure-property relationship between different structures and intrinsic thermal conductivity. Therefore, it is necessary to build a database of intrinsic thermal conductivity of polymer material structures.

[0005] However, due to the extremely low intrinsic thermal conductivity of polymers, the heat flux is very small, which poses a significant problem for measurement. Traditional measurement methods, including time-domain thermal reflectometry and heat flux meter methods, have drawbacks such as low measurement accuracy, excessive time consumption, and small measurement range. Summary of the Invention

[0006] To address the aforementioned shortcomings in the prior art, this invention provides a method for measuring the thermal conductivity of frequency domain thermal reflection spot shift.

[0007] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for measuring the thermal conductivity of frequency-domain thermal reflectance spot shift includes the following steps: S1. Prepare the measurement sample by depositing a metal film on the substrate and then depositing the sample to be measured on the metal film. S2. Construct an optical path system, using a heating laser and a probe laser to irradiate the sample surface together, and align the two laser beams through optical path calibration. S3. Adjust the offset between the probe laser and the heating laser, and modulate the frequency of the heating laser to collect the spot position signal at different frequencies; S4. Obtain the thermal diffusivity of the sample through signal analysis, and calculate the thermal conductivity of the sample by combining it with the volumetric heat capacity.

[0008] Furthermore, in S1, the metal film is an aluminum film, prepared by thermal evaporation or magnetron sputtering, and the substrate is a silicon dioxide wafer or a calcium fluoride wafer.

[0009] Furthermore, the optical path system includes a probe laser (1), a first plane mirror (2), a second plane mirror (4), a third plane mirror (9), a heating laser (3), a polarized spectrometer (7), a non-polarized spectrometer (8), a sample stage (5), an objective lens (6), a short-wavelength filter (11), and a four-quadrant detector (12). The probe laser and the heating laser are focused onto the sample surface by the spectrometer and the objective lens, and the reflected light enters the detector through the filter.

[0010] Furthermore, the optical path calibration in S2 specifically includes the following steps: S21. Simultaneously start the detection laser and the heating laser, and set the heating laser to the signal generator modulation mode; S22. The probe laser is reflected by a plane mirror to a non-polarized spectrometer, and the heated laser is reflected by a plane mirror to a polarized spectrometer; S23. Adjust the polarization spectrometer to allow the P-polarized light of the probe laser to pass through, and configure the non-polarization spectrometer to only reduce the energy of the heating laser. S24. Focus the two laser beams onto the sample surface through the objective lens, and turn on the plane mirror to allow the reflected light to enter the camera. S25. Adjust the distance between the objective lens and the sample until the camera displays a clear diffraction spot; S26. Close the plane mirror so that the light passes through the short-wave filter and is then introduced into the four-quadrant detector; S27. Adjust the XYZ three-axis moving platform of the detector to make the X / Y signal voltage close to 0V; S28. Fine-tune the position of the polarization spectrometer to confirm that the two laser beams are completely overlapped.

[0011] Furthermore, step S3 specifically includes the following steps: S31. Measure the displacement coefficient of the polarization spectrometer displacement device, confirm that the light offset corresponding to each division of the micrometer is within the preset threshold, and control the displacement device to generate the predetermined offset through the micrometer. S32. Modulate the heating laser frequency using a signal generator, and use LabVIEW program to integrate and control the frequency scanning process; S33. Record the X / Y signals output by the lock-in amplifier at each frequency point and automatically generate a text-formatted data file containing the frequency, X signal, and Y signal; S34. After completing the full-band scan, save the raw data for subsequent analysis.

[0012] The present invention has the following beneficial effects: This invention is a non-contact measurement method, which avoids requirements on the size of the sample itself, avoids errors caused by different contact conditions when the sensor and the sample are in contact, and also avoids the thermal insulation requirements of the measurement environment based on the Fourier law measurement principle. This invention demonstrates, through sensitivity calculation, that this method can significantly improve the measurement accuracy of intrinsic thermal conductivity of polymer materials, with good repeatability. Especially for materials with low thermal conductivity, the measurement range can reach 0.1-900 J / (m K), greatly expanding the measurement range of the system.

[0013] This invention has no requirements for sample size and has low requirements for surface flatness, only requiring a certain sample scattering rate, thus making sample preparation simple.

[0014] This invention enables rapid measurement, reducing steady-state measurement time from several hours to 180 seconds, significantly shortening measurement time and cost. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the frequency domain thermal reflection spot shift thermal conductivity measurement method of the present invention.

[0016] Figure 2 This is a schematic diagram of the optical path system structure according to an embodiment of the present invention.

[0017] Figure 3 This is a physical diagram illustrating the relationship between laser offset and spot position signal in an embodiment of the present invention.

[0018] Figure 4 This is a schematic diagram illustrating the change in the emission angle of a metal surface after a slight deformation is caused by direct laser irradiation in an embodiment of the present invention, resulting in a laser deflection.

[0019] Figure 5a This is a diagram illustrating the effectiveness analysis of the silica standard sample in an embodiment of the present invention.

[0020] Figure 5b This is a graph showing the effectiveness analysis of calcium fluoride standard samples in an embodiment of the present invention.

[0021] Explanation of reference numerals in the attached figures: 1-Detector laser, 2-First plane mirror, 3-Heating laser, 4-Second plane mirror, 5-Sample, 6-Objective lens, 7-Polarized spectrometer, 8-Non-Polarized spectrometer, 9-Third plane mirror, 10-Camera, 11-Shortwave filter, 12-Four-quadrant detector. Detailed Implementation

[0022] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0023] A method for measuring the thermal conductivity of frequency-domain thermal reflectance spot shift, such as... Figure 1 As shown, it includes the following steps: S1. Prepare the measurement sample by depositing a metal film on the substrate and then depositing the sample to be measured on the metal film. First, a sample to be measured is prepared. An aluminum film is deposited on a substrate, which is usually a silicon dioxide wafer or a calcium fluoride wafer. Aluminum deposition is usually carried out by thermal evaporation or magnetron sputtering. A layer of the sample to be measured is then deposited on the aluminum film. The role of aluminum is to absorb heat and generate a temperature field. After obtaining the sample to be measured, it is placed on the sample platform for testing.

[0024] S2. Construct an optical path system, using a heating laser and a probe laser to irradiate the sample surface together, and align the two laser beams through optical path calibration. like Figure 2As shown, the probe laser 1 and the heating laser 3 are first turned on simultaneously. After being reflected by the first plane mirror 2 and the second plane mirror 4, they pass through the non-polarized beam splitter 8 and the polarized beam splitter 7, respectively. The purpose is to focus the P-polarized light of the probe laser onto the sample 5 platform through the objective lens 6. The non-polarized beam splitter only weakens the energy of the heating laser and does not affect the polarization state of the light. Then, the P-polarized light passes through the polarized beam splitter 7 and enters the objective lens 6, and is then focused onto the surface of the sample 5. At this time, both beams will be emitted on the sample surface and will pass through the objective lens 6, the polarized beam splitter 7, and the non-polarized beam splitter 8. The third plane mirror 9 is a plane mirror whose opening and closing state can be controlled. When the third plane mirror 9 is in the open state, the two reflected light beams are reflected into the camera 10 through the plane mirror. At this time, the system is a microscope system. The light spots formed by the two light beams can be seen on the camera. Adjusting the exposure parameters and adjusting the distance between the sample 5 and the objective lens 6 can achieve the focusing state. At this time, a system of diffraction light spots can be seen in the camera, indicating that the focusing is successful. The reflected light spot energy is the most concentrated at this time, which is also the state we need for measurement. Adjusting the position of 7 can modulate the position of the heating laser 3 until it roughly coincides with the light spot of the detection laser 1 in the camera. In order to more accurately control the two light spots to be in the overlapping state, the signal needs to be processed. The three-plane mirror 9 is closed, allowing the light to pass through the short-wavelength filter 11. This means the shorter wavelength 640nm (heating laser wavelength 660nm) of the probe laser passes through the filter and enters the four-quadrant detector 12. To obtain the maximum signal, this light needs to be in the center of the four-quadrant detector. The XYZ three-axis moving platform can be used to adjust the detector position until the small voltage meter connected to the detector's X / Y signals approaches 0V. At this point, it indicates that the detector is in the center position, and the corresponding lock-in amplifier signal is at its maximum. Then, the position of the polarization spectrometer 7 is slightly adjusted, and the lock-in amplifier signal is observed to ensure complete overlap of the two laser beams. This is the beam overlap calibration. The next step is to adjust the displacement between the probe laser and the heating laser. This step requires measuring the displacement coefficient of 7. The displacement device corresponding to the polarization spectrometer is called a gimbal. We designed a sample stage to place the polarization beam splitter. The gimbal has two displacement directions, both controlled by a micrometer. We measured the offset of the light at sample 5 corresponding to each micrometer division, which is approximately 2.6 micrometers. In actual measurement, by rotating different numbers of divisions, different offsets can be generated between the probe laser and the heating laser. After generating this offset, the X and Y signals corresponding to the lock-in amplifier can be measured to analyze the thermal conductivity of the sample.

[0025] S3. Adjust the offset between the probe laser and the heating laser, and modulate the frequency of the heating laser to collect the spot position signal at different frequencies; like Figure 3As shown, after signal acquisition, mathematical analysis was performed on the obtained signal. The thermal diffusivity of the sample was obtained using an isotropic free thermal expansion model. The volumetric heat capacity of the sample was measured using a differential scanning calorimeter (DSC). The thermal conductivity of the sample could be obtained by combining the thermal diffusivity and volumetric heat capacity parameters.

[0026] The principle behind obtaining thermal conductivity in step S3 by combining different lock-in amplifier X / Y signals obtained at different frequencies with volumetric heat capacity is as follows: A heated laser passes through the sample and strikes the aluminum surface. After being absorbed by the aluminum, it generates a temperature field. Under the influence of this temperature field, if the probe laser deviates from the heated laser, refraction occurs, producing a spot position signal θ at the light exit point. This signal is the lock-in amplifier X / Y signal, where X is the real part of θ and Y is the imaginary part. Keeping the deviance constant, changing different frequencies yields a series of different θ values. The frequency at which the Y signal reaches its maximum value is the characteristic frequency. Analyzing this frequency reveals the characteristic thermal expansion coefficient of the sample, and combining this with the volumetric heat capacity yields the thermal conductivity.

[0027] According to the theory of free thermal diffusion, the isotropic free thermal diffusion model only considers deformation caused by thermal expansion and ignores other factors. Assuming the material is a semi-infinite solid with isotropic elastic and thermal expansion properties, the heating laser heats the metal coating, causing a temperature field. This temperature field is obtained from the Fourier heat conduction equation and also includes the probe laser deflection given the temperature field, such as... Figure 4 As shown.

[0028] The heating laser exhibits cylindrical symmetry, as do the temperature field T and displacement field u. Therefore, the Hankel transformation is used to simplify the calculation. The center of the heating laser is located at a radius r of zero, while the surface of the material under test is located at a z-zero point.

[0029] The displacement field is decomposed into a combination of scalar and vector potentials using Helmholtz's theorem.

[0030] in, It is a scalar potential. It is a vector potential.

[0031] The partial derivatives of the displacement field in the r and z directions are:

[0032] Vector potential quilt The governing equations for elastic forces are defined as follows:

[0033]

[0034] This equation describes the thermal stress caused by temperature changes under stress-free conditions at the interface between a metallic coating and a bulk material. In this case, it is used to calculate the distribution of thermal stress due to temperature changes, as well as the thermal expansion behavior of the material.

[0035] In the formula, , These are two independent elastic constants that describe the deformation of an elastic medium (such as a solid material) when subjected to force. It is the linear coefficient of thermal expansion.

[0036] Under stress-free conditions, it means that the stress at the interface is zero, that is, the metal coating and the bulk material can expand or contract freely at the interface without exerting stress on each other.

[0037] Under the condition that the interfacial stress is zero:

[0038] By combining the strain-displacement relationship with equation (1) of the displacement field equation using Hooke's law, the stress can be... Using scalars of the displacement field respectively With vector It indicates. Considering

[0039]

[0040] According to Fourier heat conduction theory, the Hankel transform (transforming the coordinate system r into the temperature system k) and the Fourier transform (transforming the time domain t into the frequency domain ω) can transform the governing equation of the elastic force into:

[0041]

[0042] The boundary conditions become:

[0043]

[0044] Therefore, after Fourier and Hankel transforms, the Fourier thermal conductivity temperature field expression is:

[0045] in, It refers to the thermal conductivity in the vertical plane and within the plane. It is volumetric heat capacity (measured by a DSC instrument).

[0046] The temperature field in the block material is:

[0047] Surface temperature in the formula The heat transfer matrix method for semi-infinite air / metal coating / semi-infinite material systems has been used in the literature, assuming known thermal conductivity and volumetric heat capacity, and is applicable to each layer. When z approaches positive infinity, it is an adiabatic boundary condition, and the heat flux boundary condition applies to the air-metal interface. In this case, the heat flux is expressed as:

[0048] In the formula The fundamental power of the modulated heating laser. It is the beam waist radius of the heating laser, that is, the energy distribution at the edge of the laser beam decreases to 1 / e. 2 The diameter of the laser spot is measured at the time of laser exit. This parameter is available when the laser exits the laser beam, and the beam waist radius can also be obtained experimentally.

[0049] When studying heat conduction in a semi-infinite air / metal coating / semi-infinite material system, the surface temperature can be solved using the transfer matrix method, as described in detail in the literature. This method is applicable to the heat conduction problem of each layer in the system, provided that the thermal conductivity and volumetric heat capacity of that layer are known. As z→±∞, the system satisfies the adiabatic boundary condition, meaning that heat will not be lost through the boundary. At the air-metal interface, the heat flux boundary condition is applied, where the heat flux is equal to the fundamental harmonic amplitude of the modulated pump laser absorption power, and is the radius of the pump beam.

[0050] S4. Obtain the thermal diffusivity of the sample through signal analysis, and calculate the thermal conductivity of the sample by combining it with the volumetric heat capacity.

[0051] Based on the given temperature field, we can obtain a general solution to the governing equations. This solution considers the thermophysical properties of each material layer and the heat flux conditions at the interfaces, thus accurately describing the temperature distribution throughout the system. This transfer matrix method is particularly effective in dealing with heat conduction problems in multilayer materials because it can handle complex boundary conditions and material properties. Using this method, researchers can predict and control the temperature distribution in different material layers, which is crucial for many engineering applications such as thermal management, materials science, and energy technologies.

[0052]

[0053]

[0054] constant The result after boundary condition processing is:

[0055]

[0056] After solving for the general solution, the two key constants can be explained by the following formula: in the free thermal diffusion model, the displacement at the zero point on the surface. It can be expressed by the following formula:

[0057] In most cases, the characteristic frequencies are at low frequencies.

[0058] The reason is:

[0059] Assuming the heating laser beam waist radius Characteristic frequencies in relative extreme cases speed of sound therefore The characteristic frequency is generally less than 1MHz because the characteristic frequency decreases as thermal diffusivity decreases. The 1MHz data was obtained under testing of gold, a material with ultra-high thermal diffusivity.

[0060] Combining the two equations above, we can obtain:

[0061] The second equation is derived from the elastic properties and Poisson's ratio. The conversion formula between the two is obtained. Under the low-frequency assumption, the surface deformation is not significantly dependent on the frequency, which is advantageous for measuring thermal conductivity, heat capacity and coefficient of thermal expansion in the frequency domain.

[0062] The surface deformation in real space can then be obtained by using the inverse Hankel transformation:

[0063] Therefore, the surface slope can be obtained.

[0064]

[0065] When the surface slope is nearly constant within the probe laser radius, the deflection angle of the probe beam will simply be twice the surface slope. However, this condition is not easily satisfied in typical experiments because the radius of the probe beam is comparable to that of the heating beam. Our previous research showed that the convolution of the probe light intensity with the surface slope can well describe the deflection angle of the probe beam. This discovery is significant for understanding and applying optical probe techniques, especially in experiments requiring precise measurements of surface properties. Through this convolution method, we can more accurately predict and control the behavior of the probe beam, thereby improving the reliability and effectiveness of our experiments.

[0066] The formula for the deflection angle is as follows:

[0067] in the formula It is a constant independent of the material, with a value of approximately 1. It involves heating the laser and detecting the beam waist radius of the laser. It involves detecting the offset between the laser and the heating laser.

[0068] The above formula is based on the premise that, at the modulation frequency, the deflection of the probe laser is unaffected by the steady-state surface deformation caused by the heating laser, the DC portion of the heating laser power is also unaffected, and the linear superposition principle applies to surface deformation. If the product of the coefficient of thermal expansion and temperature drift is sufficiently small, then the radius of curvature of the sample surface can be sufficiently large compared to the focusing length of the objective lens, making our method applicable. Therefore, the deflection angle can be measured. The coefficient of thermal expansion can be obtained by transformation. Thus, the thermal conductivity is obtained. ,like Figure 5a and Figure 5b As shown.

[0069] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0070] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0071] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0072] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

[0073] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A method for measuring the thermal conductivity of frequency-domain thermal reflectance spot shift, characterized in that, Includes the following steps: S1. Prepare the measurement sample by depositing a metal film on the substrate and fabricating the sample to be measured on the metal film; S2. Construct an optical path system, using a heating laser and a probe laser to irradiate the sample surface together, and align the two laser beams through optical path calibration. S3. Adjust the offset between the probe laser and the heating laser, and modulate the frequency of the heating laser to collect the spot position signal at different frequencies; S4. Obtain the thermal diffusivity of the sample through signal analysis, and calculate the thermal conductivity of the sample by combining it with the volumetric heat capacity.

2. The method for measuring the thermal conductivity of frequency-domain thermal reflection spot shift according to claim 1, characterized in that, The metal film in S1 is an aluminum film, prepared by thermal evaporation or magnetron sputtering, and the substrate is a silicon dioxide wafer or a calcium fluoride wafer.

3. The method for measuring the thermal conductivity of frequency-domain thermal reflection spot shift according to claim 1, characterized in that, The optical path system includes a probe laser (1), a first plane mirror (2), a second plane mirror (4), a third plane mirror (9), a heating laser (3), a polarized spectrometer (7), a non-polarized spectrometer (8), a sample stage (5), an objective lens (6), a short-wavelength filter (11), and a four-quadrant detector (12). The probe laser and the heating laser are focused onto the sample surface by the spectrometer and the objective lens, and the reflected light enters the detector through the filter.

4. The method for measuring the thermal conductivity of frequency-domain thermal reflection spot shift according to claim 1, characterized in that, The optical path calibration in S2 specifically includes the following steps: S21. Simultaneously start the detection laser and the heating laser, and set the heating laser to the signal generator modulation mode; S22. The probe laser is reflected by a plane mirror to a non-polarized spectrometer, and the heated laser is reflected by a plane mirror to a polarized spectrometer; S23. Adjust the polarization spectrometer to allow the P-polarized light of the probe laser to pass through, and configure the non-polarization spectrometer to only reduce the energy of the heating laser. S24. Focus the two laser beams onto the sample surface through the objective lens, and turn on the plane mirror to allow the reflected light to enter the camera. S25. Adjust the distance between the objective lens and the sample until the camera displays a clear diffraction spot; S26. Close the plane mirror so that the light passes through the short-wave filter and is then introduced into the four-quadrant detector; S27. Adjust the XYZ three-axis moving platform of the detector to make the X / Y signal voltage close to 0V; S28. Fine-tune the position of the polarization spectrometer to confirm that the two laser beams are completely overlapped.

5. The method for measuring the thermal conductivity of frequency-domain thermal reflection spot shift according to claim 1, characterized in that, S3 specifically includes the following steps: S31. Measure the displacement coefficient of the polarization spectrometer displacement device, confirm that the light offset corresponding to each division of the micrometer is within the preset threshold, and control the displacement device to generate a predetermined offset through the micrometer. S32. Modulate the heating laser frequency using a signal generator, and use LabVIEW program to integrate and control the frequency scanning process; S33. Record the X / Y signals output by the lock-in amplifier at each frequency point and automatically generate a text-formatted data file containing the frequency, X signal, and Y signal; S34. After completing the full-band scan, save the raw data for subsequent analysis.

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