High-pressure low-temperature in-situ thermal conductivity measuring device and method based on diamond anvil cells

Abstract

The invention discloses a high-pressure low-temperature in-situ thermal conductivity measuring device and method based on diamond anvil cells, and belongs to the technical field of high-pressure thermophysical property measurement. The high-pressure low-temperature in-situ thermal conductivity measuring device based on the diamond anvil cell is composed of a diamond anvil cell high-pressure generation device (1), an extreme low temperature generation and temperature control device (2) and a time-domain heat reflection thermophysical property measuring system (3). The measuring method comprises the steps of cutting a sample, depositing an aluminum film, packaging and pressurizing, setting temperature, fitting parameters and the like. According to the invention, a non-contact thermal conductivity measurement technology is adopted, so that the assembling difficulty of the diamond anvil cell sample is effectively reduced, and the introduction of experimental errors caused by excessive heat contact is avoided.

Description

Technical field:

[0001] The invention belongs to the technical field of high-pressure thermal property measurement, and in particular relates to a diamond anvil cell high-pressure generating device, an extreme low-temperature generating and temperature controlling device, and a time-domain thermal reflection thermal property measuring system. Background technology:

[0002] Technological innovation is an important driving force for scientific development. In the field of high-pressure science, the importance of technological innovation is particularly prominent. Since its birth, the diamond anvil cell ultrahigh pressure technology has achieved remarkable achievements in the research of material property regulation. Nearly half of the superconducting elements in the periodic table are obtained by ultrahigh pressure. For the high-pressure research of hydrides, it is even more advanced at 203K (H3S) and even 250K (LaH 10 ) discovered a superconducting transition, which is much higher than the McMillan superconducting temperature limit (40K) based on the BCS theory. The relevant explanation needs further improvement of the high-temperature superconductivity theory.

[0003] In fact, as early as 1950, Frohlich's team had already realized that T c The conductivity of high-performance superconducting materials is very poor at room temperature, indicating that electron-phonon interaction is the main cause of superconductivity at low temperatures. However, as an effective means to analyze electron-phonon interaction, the measurement of thermal conductivity under high pressure and low temperature conditions still faces severe challenges. Therefore, it is urgent to achieve in-situ measurement of high-pressure and low-temperature thermal conductivity through the innovation of technical methods, thereby providing a broader perspective for high-pressure scientific research such as superconductivity. Summary of the invention:

[0004] The present invention proposes a low-temperature thermal conductivity measurement device and method based on a diamond anvil to solve the problem of in-situ measurement of high-pressure and low-temperature thermal conductivity.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows:

[0006] A high-pressure and low-temperature in-situ thermal conductivity measuring device based on a diamond anvil, which is composed of a diamond anvil high-pressure generating device 1, an extreme low-temperature generating and temperature controlling device 2, and a time-domain thermal reflection thermal property measuring system 3;

[0007] The diamond anvil high pressure generating device 1 comprises: a diamond anvil 101, a sealing gasket 102, an aluminum film 104, a pressure transmission medium 105, a ruby ​​106, and a press body 107; the position relationship of the diamond anvil 101, the sealing gasket 102, and the press body 107 is symmetrical along the central axis, and from the inside to the outside, they are the sealing gasket 102, the diamond anvil 101, and the press body 107;

[0008] The extremely low temperature generation and temperature control device 2 comprises: a thermostat 201, a vacuum pump group 202, a liquid helium dewar tank 203, a secondary cold head 204, a water-cooled compressor 205, a helium circulation pump 206, a helium buffer chamber 207, and a data temperature control system 208; the position relationship of each component of the extremely low temperature generation and temperature control device 2 is as follows according to the order in which helium flows: a liquid helium dewar tank 203, a secondary cold head 204, a thermostat 201, a helium circulation pump 206, a helium buffer chamber 207, and then flows through the secondary cold head 204 again to realize a helium closed loop;

[0009] The time-domain thermal reflection thermal property measurement system 3 includes: a laser emitter 301, an optical isolator 302, a first 1 / 2 glass slide 303, a first polarization beam splitter prism 304, a BBO crystal 305, a first reflector 306, an electro-optic modulator 307, an analog signal driver 308, a phase-locked amplifier 309, a cold mirror 310, a 10x objective lens 311, a beam expander 312, a second reflector 313, a linear displacement platform 314, a second 1 / 2 glass slide 315, a second polarization beam splitter prism 316, a 1 / 4 glass slide 317, a plano-convex lens 318, a green light filter 319, a photodetector 320, an Al film reflector 321, a CCD camera 322, and a data acquisition system 323; the position relationship of each optical component is in the order of the laser light path, which is: a laser emitter 301, an optical isolator 30 2. The first 1 / 2 glass slide 303 and the first polarization beam splitter prism 304. The laser is divided into two beams, one for the pumping laser and the other for the detection laser. The pumping laser optical path includes: BBO crystal 305, first reflector 306, electro-optic modulator 307, cold mirror 310, 10x objective lens 311 and the sample to be tested 103. The other detection laser optical path includes: beam expander 312, second reflector 313, linear displacement platform 314, second 1 / 2 glass slide 315, second polarization beam splitter prism 316, 1 / 4 glass slide 317, cold mirror 310, 10x objective lens 311 and the sample to be tested 103. The reflected optical path of the detection laser includes: 10x objective lens 311, cold mirror 310, 1 / 4 glass slide 317, second polarization beam splitter prism 316, plano-convex lens 318, green light filter 319 and photodetector 320.

[0010] Furthermore, the functions and parameters of the components in the diamond anvil high pressure generating device 1 are as follows:

[0011] The diamond anvil 101 is a diamond with a flattened top. The flattened surface is called anvil surface. Using two diamond anvils 101 to press the sample 103 to be tested can produce a high-pressure environment. A pair of diamond anvils 101 with an anvil surface diameter of 150 μm can achieve an experimental pressure of more than 100 GPa.

[0012] The sealing gasket 102 is made of T301 steel sheet or metal rhenium sheet, and its function is to seal the sample 103 to be tested, so as to prevent the sample 103 to be tested from being squeezed and extended beyond the diamond anvil surface, thereby ensuring the loading of higher experimental pressure;

[0013] The aluminum mold 104 is deposited on the surface of the sample 103 to absorb the pumping laser and reflect the detection laser, thereby recording the change of the temperature rise of the sample 103 to be tested over time;

[0014] The pressure transmission medium 105 used in the present invention is silicone oil, which is used to provide hydrostatic pressure for the experiment;

[0015] The function of the ruby ​​106 is to record the pressure environment of the experimental process of the present invention in real time through the fluorescence peak;

[0016] The press body 107 is a metal mechanical component, and its function is to fix and adjust the position of the diamond anvils 101 to ensure that the anvil surfaces of the two diamond anvils 101 are parallel and aligned.

[0017] Furthermore, the functions and parameters of the components in the extreme low temperature generation and temperature control device 2 are as follows:

[0018] The diamond anvil high pressure generating device 1 is placed inside the thermostat 201 to provide a variable temperature environment for the experiment. The fastest cooling speed can reach 15 minutes to 5K. Combined with the vacuum pump group 202, the experimental temperature range of the thermostat 201 is 2-800K, and the temperature control accuracy of the data temperature control system 208 is 50mK.

[0019] The vacuum pump group 202 is composed of a mechanical pump and a molecular pump, and its function is to provide vacuum for the thermostat 201, thereby achieving a lower temperature experimental environment;

[0020] The function of the secondary cold head 204 is to compress the helium released from the liquid helium dewar 203 into liquid helium, and the compression process is achieved by the water-cooled compressor 205;

[0021] The helium circulation pump 206 is used to recover the liquid helium or helium gas released by the thermostat 201 and send it back to the secondary cold head 204 via the helium buffer chamber 207;

[0022] Furthermore, the functions and parameters of each component in the time-domain thermal reflection thermal property measurement system 3 are as follows:

[0023] The laser emitter 301 outputs a pulsed laser with a wavelength of 1064 nm, a repetition frequency of 80 MHz and a pulse width of 100 fs, which is linearly polarized light;

[0024] The material of the BBO crystal 305 is β-phase barium borate, which is used to convert the original pumping laser wavelength of 1064nm into a green pumping light of 532nm wavelength, so as to effectively reduce the influence of the pumping laser on the detection signal;

[0025] The linear displacement platform 314 has a total travel of 300 mm. The detection light makes 12 turns on the displacement platform, which can provide a maximum delay time of 12 ns.

[0026] A high-pressure and low-temperature in-situ thermal conductivity measurement method based on a diamond anvil cell comprises the following steps:

[0027] Step 1), the sample 103 to be tested is polished or extruded to 10-20 μm, cut into square pieces of a specified size according to the requirements, and then a magnetron sputtering device is used to deposit an aluminum film 104 of 100 nm on the surface of the sample 103 to be tested;

[0028] Step 2), placing the sample 103 to be tested prepared in step 1) at a designated position of the sample chamber of the diamond anvil cell high pressure generating device 1, encapsulating it with a pressure transmitting medium 105, and loading it to a target experimental pressure;

[0029] Step 3), placing the diamond anvil high pressure generating device 1 assembled in step 2) inside the thermostat 201, and setting the target experimental temperature through the temperature control system 208;

[0030] Step 4), observing the light spot on the surface of the sample 103 to be tested by the CCD camera 322, ensuring that the pumping laser and the detection laser in the time-domain thermal reflection thermal property measurement system 3 are focused on the surface of the sample 103 to be tested;

[0031] Step 5), using the time domain thermal reflection thermal property measurement system 3 to measure the change of the surface temperature rise of the sample 103 to be tested over time, by adjusting the sample fitting parameters, the calculated signal is made to match the experimental measurement data, and then the thermal conductivity of the sample 103 to be tested under the experimental temperature and pressure is determined.

[0032] The technical effects and advantages of the present invention are:

[0033] The present invention provides a method for measuring high-pressure and low-temperature in-situ thermal conductivity, and designs a corresponding experimental device. The temperature control system can achieve high-precision temperature control in the experimental range of 2-800K, and the experimental temperature basically covers the research fields of material superconductivity, thermoelectricity and other physical properties; the time-domain thermal reflection non-contact technical means is more suitable for the measurement of high-pressure thermal properties, because the size of the diamond anvil sample is only in the micron order, and the contact-type thermal property measurement will not only increase the difficulty of experimental operation, but also aggravate the introduction of experimental errors; the experimental process of the present invention is relatively simple and easy to operate, and is suitable for high-pressure in-situ characterization of thermal conductivity of bulk and thin film. Description of the drawings:

[0034] Figure 1 It is a schematic cross-sectional diagram of the assembly of a diamond anvil cell sample according to an embodiment of the present invention.

[0035] Figure 2 Schematic diagram of the structure of various components of the low-temperature temperature control system according to an embodiment of the present invention.

[0036] Figure 3 Schematic diagram of the structure of the time-domain thermal reflection optical path system according to an embodiment of the present invention.

[0037] Figure 4 These are the experimental measurements and numerical fitting results of Fe in the embodiments of the present invention. Specific implementation method:

[0038] The technical idea of ​​the high-pressure and low-temperature in-situ thermal conductivity measurement method provided by the present invention is as follows: a diamond anvil high-pressure generating device 1 is used to extrude a sample 103 to generate a target pressure; the high-pressure generating device 1 is then placed inside a thermostat 201, and the experimental temperature is regulated by a low-temperature temperature control system 208; and finally, a time-domain thermal reflection system 3 is used to measure the thermal conductivity of the sample 103 to be tested under the target temperature and pressure conditions.

[0039] To ensure the effective promotion of the technical solution of the present invention, the present invention will be described in detail below in conjunction with implementation cases. It is worth emphasizing that the purpose of describing the examples is to enhance the understanding of the present invention, and it is not intended to limit the implementation methods of the present invention.

[0040] Embodiment 1: Combination Figure 1 Explain how to achieve target pressure loading of the sample

[0041] Step 1: Fix the cleaned diamond anvil 101 inside the press body 107. In this case, the anvil surface of the diamond anvil 101 has a diameter of 300 μm. The device is adjusted to ensure that the anvil surfaces of the two diamond anvils 101 are parallel and in concentric circles.

[0042] Step 2: Use the diamond anvil device prepared in the first step to press the 250 μm thick metal rhenium sheet 102 to 25-50 μm, then use a laser cutting device to punch a hole in the center of the indentation of the pre-pressed metal rhenium sheet 102 as a sample cavity, and the diameter of the sample cavity is 180 μm;

[0043] Step 3: polish or extrude the sample 103 to a thickness of 10 to 20 μm, cut it into square pieces of 40*40 μm, and then deposit an aluminum film 104 with a thickness of 100 nm on the surface of the sample 103 using a magnetron sputtering device;

[0044] Step 4: Reset the metal rhenium sheet 102 prepared in step 2, and then place the sample 103 and ruby ​​​​105 in the designated position of the sample chamber in sequence, as shown in the attached Figure 1 As shown, finally, the remaining space of the sample cavity is filled with silicone oil 106 for packaging;

[0045] Step 5: Use the Raman device to calibrate the fluorescence peak of the ruby ​​105 to record the experimental pressure of the sample 103 to be tested, and adjust the force of squeezing the two diamond anvils 101 through mechanical components to achieve the loading of the target pressure.

[0046] Embodiment 2: Combination with Figure 2 Explain how to achieve sample target temperature control

[0047] Step 1: Fix the diamond anvil high pressure generating device 1 assembled in Example 1 inside the cavity of the thermostat 201, and pump the air pressure of the thermostat 201 to 10 -4 mbar, close the vacuum valve of the thermostat 201, and then close the vacuum pump unit 202;

[0048] Step 2: Slowly open the liquid helium dewar 203 to ensure that the air pressure flowing through the secondary cold head 204 is maintained at ~5psi, and the helium fills the entire cryogenic system. Open the helium buffer chamber 207 vent valve and release the air for 1-2 minutes. At this time, there is no air remaining in the cryogenic system, and then close the helium buffer chamber 207 vent valve;

[0049] Step 3: Turn on the water-cooled compressor 205 and the liquid helium circulation pump 206; the function of the water-cooled compressor 205 is to liquefy the helium flowing through the secondary cold head 204, and then the liquid helium flows through the thermostat 201 to achieve temperature control of 4K or even lower than 4K; the function of the helium circulation pump 206 is to collect the liquid helium / helium flowing out of the thermostat 201, and then inject it into the secondary cold head 204 through the helium buffer chamber 207, in order to achieve the recycling of helium.

[0050] Step 4: Set the target experimental temperature through the temperature control system 208, and then measure the thermal conductivity of the sample 103 to be tested in combination with the time domain thermal reflection optical path system 3. The principle of temperature control is that the thermostat 201 has a built-in heating resistor, and the temperature control system 208 adjusts the heating resistor current, and finally achieves the target temperature setting in combination with the liquid helium flowing through the thermostat 201. The experimental temperature is recorded by a thermocouple in the thermostat 201 close to the diamond anvil 101.

[0051] Embodiment 3: Combination Figure 3 Explain the composition and working principle of the time domain thermal reflection optical path

[0052] According to the order of laser passing: the laser emitter 301 outputs pulsed linear polarized light with a wavelength of 1064nm, which passes through the optical isolator 302, the first 1 / 2 glass slide 303 and the first polarization beam splitter prism 304 in turn. The optical isolator 302 only allows the laser to pass in one direction, isolates the back-reflected light, and prevents it from damaging the laser emitter 301; the first 1 / 2 glass slide 303 is used to adjust the polarization direction of the linear polarized light, and the first polarization beam splitter prism 304 is used to separate the horizontal polarization and vertical polarization in the linear polarized light, wherein the horizontal polarized light can be used as the pumping laser through the first polarization beam splitter prism 304, while the vertical polarized light is completely reflected as the detection laser; Brief summary: The combination of the first 1 / 2 glass slide 303 and the first polarization beam splitter prism 304 is used to divide the polarized laser into the pumping laser and the detection laser, and allocate their proportions of the total polarized laser as needed;

[0053] Among them, the pumping laser is frequency-doubled through the BBO crystal 305, and the laser with a wavelength of 1064nm is converted into 532nm, in order to distinguish the pumping laser from the detection laser, so as to reduce the influence of the pumping laser on the detection signal; the frequency-doubled pumping laser passes through the first reflector 306 and the electro-optic modulator 307 successively, and the pumping laser is loaded as a signal with a specific phase and frequency; the signal loaded by the electro-optic modulator 307 is then passed through the analog signal driver 308, and finally the pumping laser is modulated into a high-quality sinusoidal output with a frequency of 1MHz; the pumping laser continues to pass through the cold mirror 310 and the 10x objective lens 311 and finally focuses on the aluminum film 104 on the surface of the sample 103 to be tested inside the diamond anvil high-voltage generating device 1. The purpose is to apply temperature disturbance to the aluminum film 104; since there is a linear relationship between the metal reflectivity and the temperature, by measuring the reflectivity of the aluminum film 104, the change of the surface temperature of the sample 103 to be tested with time can be recorded, and then the thermal conductivity of the sample 103 to be tested can be obtained;

[0054] However, the difficulty of the experiment lies in how to identify the change of the temperature of the sample 103 to be tested over time at the nanosecond level, so the route of the detection laser needs to be designed. The detection laser reflected by the first polarization beam splitter prism 304 passes through the beam expander 312, the second reflector 313, and the linear displacement platform 314 in sequence. The function of the linear displacement platform 314 is to control the time interval between the pumping laser and the detection laser reaching the surface of the sample 103 to be tested. The total stroke of the linear displacement platform 314 is 300mm. The detection laser makes 12 turns on it, which can provide a maximum time delay of 12ns, thereby providing a time domain resolution for the experimental system; in order to avoid the spot divergence of the detection laser due to the long optical path, the present invention places a beam expander 312 between the polarization beam splitter prism 304 and the linear displacement platform 314. The beam expander 312 amplifies the laser beam by 3.3 times. The larger laser size effectively reduces the beam divergence angle, thereby reducing the influence of the linear displacement platform 314 on the laser divergence;

[0055] Finally, in order to separate the detection laser reflected from the surface of the sample 103 to be tested from the pump laser, the detection laser passing through the linear displacement platform 314 needs to pass through the second 1 / 2 glass slide 315, the second polarization beam splitter prism 316, and the 1 / 4 glass slide 317 in sequence; the second 1 / 2 glass slide 315 is used to adjust the vertical polarization direction of the detection laser to the horizontal direction, so that it can pass through the second polarization beam splitter prism 316; then the detection laser passes through the 1 / 4 glass slide 317 twice, and the polarization direction will be changed to vertical again. When it returns to the second polarization beam splitter prism 316 is completely reflected; then the detection laser is focused on the sensing area of ​​the photodetector 320 via the plano-convex lens 318 and the green light filter 319, wherein the green light filter 319 effectively isolates the influence of a small amount of pumping laser on the experimental signal, and the photodetector 320 is connected to the phase-locked amplifier 309 to realize the amplification of the collected signal; finally, a movable Al film reflector 321 is placed at the front end of the photodetector 320, and then the surface quality of the sample 103 to be tested and the focusing and overlap degree of the pumping laser and the detection laser are observed through the CCD camera 322.

[0056] Through the design of the experimental optical path, the change of the sample's temperature rise over time at the nanosecond level can be effectively detected. Combined with the experimental parameters such as the size, specific heat, density, etc. of the sample and the aluminum film, the measurement of the thermal conductivity, interface thermal resistance and other physical properties of the sample to be tested can be achieved.

[0057] Example 4: Experimental measurement of Fe thermal conductivity

[0058] In order to verify the feasibility of the experimental method of the present invention and explore the experimental accuracy, the present invention conducts experimental thermal conductivity measurement on metal Fe. The sample is selected from 99.995% iron foil of Alfa Company, and the iron foil is pre-pressed to 10μm thick by diamond anvil 101, and then cut into 40*40μm; the cut sample 103 to be tested is deposited with ~100nm thick aluminum film 104 by magnetron sputtering, and the thickness of the aluminum film 104 is calibrated by atomic force microscopy; the prepared sample 103 to be tested and ruby ​​106 are placed in the diamond anvil sample chamber in turn, and are encapsulated with silicone oil 105, and the experimental pressure is loaded to 0.5GPa. The sample assembly schematic diagram is shown in the attached figure. Figure 1 , the experimental process is detailed in Example 1.

[0059] The assembled diamond anvil cell high pressure generating device 1 is placed in the thermostat 201. This embodiment is intended to verify the feasibility of the experimental method, so the temperature and pressure are not considered. The position of the thermostat 201 is adjusted by the three-dimensional platform to ensure that the pumping laser and the detection laser are both focused on the surface of the sample 103 to be tested; the stroke of the linear displacement platform 314 is adjusted to provide the experimental system with time domain resolution, so as to obtain the curve of the reflectivity change of the sample 103 to be tested over time, as shown in the attached figure. Figure 4 shown.

[0060] The pumping laser frequency outputted by the electro-optic modulator 307 of the present invention is 80 MHz, and the pulse width is much higher than the single laser pulse width (100 fs), so the modulated sinusoidal signal can be expressed as:

[0061]

[0062] Where τ is the time interval between the pump laser and the detection laser reaching the sample surface, ω0 is the modulation frequency of the electro-optic modulator, and the expression of the pump laser in the frequency domain is:

[0063]

[0064] Where Q pump is the energy of a single pump laser pulse, T is the time interval between adjacent pulses, T0 is a delay time of any length, ω s is the repetition frequency of the laser pulse. Therefore, the temperature response of the measured sample surface can be expressed as:

[0065]

[0066] H(ω) is the pulse response of the sample under test to the unit intensity pump laser in the frequency domain. The sample in the diamond anvil is a bidirectional heat transfer model, so:

[0067]

[0068] Where R pump and R probe are the spot radii of the pumping laser and the detection laser, respectively, and C1, C2, D1, and D2 are functions of the thermal conductivity and specific heat of the sample, Al film, and silicone oil. So far, when other parameters are known, the signal of the lock-in amplifier 309 can be analyzed through the heat transport model, and the fitting parameters can be further adjusted to make the calculated signal consistent with the experimental measurement signal, so as to determine the thermal physical parameters of the sample.

[0069] In this embodiment, the thickness of the sample, aluminum film and silicone oil are 10 μm, 100 nm and 20 μm respectively. The thermal conductivity of the aluminum film and silicone oil are 235 W / m·K and 1.3 W / m·K respectively. The volume heat capacity of the sample, aluminum film and silicone oil are 3.616 J cm -3 K -1 , 2.684 J cm -3 K -1 and 2.552 J cm -3 K -1 The interface thermal conductivity of silicone oil / aluminum film and aluminum film / sample is 350MW m -2 K -1Combined with the above experimental parameters, the thermal conductivity of Fe obtained by the present invention is finally fitted to be 85.55 W / m·K, which is slightly higher than the value of 80 W / m·K reported in the literature. This is due to the loading of the experimental pressure, and the experimental accuracy is within the acceptable range. The feasibility of the experimental method of the present invention is verified by the experimental measurement of the thermal conductivity of Fe.

Claims

1. A high-pressure and low-temperature in-situ thermal conductivity measurement device based on a diamond anvil, comprising a diamond anvil high-pressure generating device (1), an extreme low-temperature generating and temperature control device (2), and a time-domain thermal reflection thermal property measurement system (3); The diamond anvil cell high pressure generating device (1) comprises: A diamond anvil (101), a sealing gasket (102), an aluminum film (104), a pressure transmission medium (105), a ruby ​​(106), and a press body (107); the diamond anvil (101), the sealing gasket (102), and the press body (107) are symmetrically positioned along the central axis, and from the inside to the outside are the sealing gasket (102), the diamond anvil (101), and the press body (107); The extremely low temperature generation and temperature control device (2) comprises: a thermostat (201), a vacuum pump group (202), a liquid helium dewar tank (203), a secondary cold head (204), a water-cooled compressor (205), a helium circulation pump (206), a helium buffer chamber (207), and a data temperature control system (208); the position relationship of the components of the extremely low temperature generation and temperature control device (2) is, according to the order in which helium flows, the following: a liquid helium dewar tank (203), a secondary cold head (204), a thermostat (201), a helium circulation pump (206), a helium buffer chamber (207), and a helium closed loop is realized by flowing through the secondary cold head (204) again; The time-domain thermal reflection thermal property measurement system (3) comprises: a laser emitter (301), an optical isolator (302), a first 1 / 2 glass slide (303), a first polarization beam splitter (304), a BBO crystal (305), a first reflector (306), an electro-optic modulator (307), an analog signal driver (308), a lock-in amplifier (309), a cold mirror (310), a 10x objective lens (311), a beam expander (312), a second reflector ( 313), a linear displacement platform (314), a second 1 / 2 glass slide (315), a second polarization beam splitter prism (316), a 1 / 4 glass slide (317), a plano-convex lens (318), a green light filter (319), a photodetector (320), an Al film reflector (321), a CCD camera (322), and a data acquisition system (323); the positional relationship of each optical component is in the order of the laser light path, in the following order: a laser emitter (301), an optical isolator (3 02), a first 1 / 2 glass slide (303), a first polarization beam splitter prism (304), the laser is divided into two beams, one is a pumping laser and the other is a detection laser; wherein the pumping laser optical path includes: a BBO crystal (305), a first reflector (306), an electro-optic modulator (307), a cold mirror (310), a 10x objective lens (311), and a sample to be tested (103); the other detection laser optical path includes: a beam expander (312), a second reflector (313), a linear displacement A platform (314), a second 1 / 2 glass slide (315), a second polarization beam splitter prism (316), a 1 / 4 glass slide (317), a cold mirror (310), a 10-fold objective lens (311), and a sample to be tested (103); a reflected light path of the detection laser: a 10-fold objective lens (311), a cold mirror (310), a 1 / 4 glass slide (317), a second polarization beam splitter prism (316), a plano-convex lens (318), a green light filter (319), and a photodetector (320).

2. The high-pressure and low-temperature in-situ thermal conductivity measurement device based on a diamond anvil according to claim 1, characterized in that: The diamond anvil (101) is a diamond with a flattened top, and the flattened surface is called anvil surface. A high-pressure environment can be generated by compressing a sample (103) to be tested with two diamond anvils (101). A pair of diamond anvils (101) with an anvil surface diameter of 150 μm can achieve an experimental pressure of more than 100 GPa. The sealing gasket (102) is made of T301 steel sheet or metal rhenium sheet, and its function is to seal the sample to be tested (103) to prevent the sample to be tested (103) from being squeezed and extended beyond the diamond anvil surface, thereby ensuring the loading of higher experimental pressure; The aluminum mold (104) is deposited on the surface of the sample to be tested (103) to absorb the pumping laser and reflect the detection laser, thereby recording the change of the temperature rise of the sample to be tested (103) over time; The pressure transmission medium (105) is silicone oil, which is used to provide hydrostatic pressure for the experiment; The ruby ​​(106) is used to record the pressure environment of the experimental process of the present invention in real time through the fluorescence peak; The press body (107) is a metal mechanical component, and its function is to fix and adjust the position of the diamond anvils (101) to ensure that the anvil surfaces of the two diamond anvils (101) are parallel and aligned.

3. The high-pressure and low-temperature in-situ thermal conductivity measurement device based on a diamond anvil according to claim 1, characterized in that: A diamond anvil high pressure generating device (1) is placed inside the thermostat (201) to provide a variable temperature environment for the experiment. The fastest cooling speed can reach 15 minutes to 5K. Combined with the vacuum pump group (202), the experimental temperature range of the thermostat (201) is 2-800K, and the temperature control accuracy of the data temperature control system (208) is 50mK. The vacuum pump group (202) is composed of a mechanical pump and a molecular pump, and its function is to provide vacuum for the thermostat (201), thereby achieving a lower temperature experimental environment; The function of the secondary cold head (204) is to compress the helium released from the liquid helium dewar (203) into liquid helium, and the compression process is achieved by a water-cooled compressor (205); The helium circulation pump (206) is used to recover the liquid helium or helium released by the thermostat (201) and send it back to the secondary cold head (204) via the helium buffer chamber (207).

4. The high-pressure and low-temperature in-situ thermal conductivity measurement device based on a diamond anvil according to claim 1, characterized in that: The laser emitter (301) outputs a pulsed laser with a wavelength of 1064 nm, a repetition frequency of 80 MHz and a pulse width of linearly polarized light of ∼100 fs; The BBO crystal (305) is made of β-phase barium borate and is used to convert the original pumping laser with a wavelength of 1064 nm into a green pumping light with a wavelength of 532 nm, so as to effectively reduce the influence of the pumping laser on the detection signal; The linear displacement platform (314) has a total travel of 300 mm, and the detection light makes 12 turns on the displacement platform, which can provide a maximum delay time of 12 ns.

5. A high-pressure and low-temperature in-situ thermal conductivity measurement method based on a diamond anvil cell, characterized in that: Using the high-pressure and low-temperature in-situ thermal conductivity measuring device based on a diamond anvil according to claim 1, the steps are as follows: Step 1), the sample to be tested (103) is polished or extruded to 10-20 μm, cut into square pieces of a specified size according to requirements, and then a magnetron sputtering device is used to deposit an aluminum film (104) of 100 nm on the surface of the sample to be tested (103); Step 2), placing the sample to be tested (103) prepared in step 1) at a designated position of the sample chamber of the diamond anvil cell high pressure generating device (1), encapsulating it with a pressure transmitting medium (105), and loading it to a target experimental pressure; Step 3), placing the diamond anvil high pressure generating device (1) assembled in step 2) inside a thermostat (201), and setting a target experimental temperature through a temperature control system (208); Step 4), observing the light spot on the surface of the sample to be measured (103) by using a CCD camera (322), ensuring that the pumping laser and the detection laser in the time-domain thermal reflection thermal property measurement system (3) are both focused on the surface of the sample to be measured (103); Step 5), using the time domain thermal reflection thermal property measurement system (3) to measure the change of the surface temperature rise of the sample to be tested (103) over time, by adjusting the sample fitting parameters, the calculated signal is made to match the experimental measurement data, and then the thermal conductivity of the sample to be tested (103) under the experimental temperature and pressure is determined.

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