Terahertz spectroscopy experimental system with liquid sample thickness adjustable device

Abstract

The utility model relates to a kind of containers of dynamic adjustment liquid thickness, specifically to a kind of terahertz spectroscopy experimental system with liquid sample thickness adjustable device, purpose is to solve the volume of liquid sample cell container in existing terahertz spectroscopy experimental system is fixed, the test thickness of measured liquid sample cannot be dynamically adjusted, leading to complex experimental process, the calculation problem of risk increase.The liquid sample cell of the utility model includes the first box and the second box that are all cuboids;Second box is set on the first slide rail, and can reciprocate along the first slide rail;First box includes first box body and the extension bottom surface of U type, the side of first box body has first opening, and the one elongated arm of extension bottom surface is communicated and coplanar with the bottom surface of first box body at first opening. When second box reciprocates along the first slide rail, the test thickness of liquid sample in liquid sample placement space is dynamically adjusted, and the experimental efficiency and result accuracy are effectively improved.

Description

Technical Field

[0001] This utility model relates to an optical characterization system, specifically to a terahertz spectroscopy experimental system with an adjustable liquid sample thickness device. Background Technology

[0002] Terahertz (THz) waves are electromagnetic waves with frequencies ranging from 0.1 THz to 10 THz (corresponding to wavelengths of 3000 μm to 30 μm). THz waves have wavelengths between microwaves and infrared waves, and their photon energy is comparable to the energy of transitions between rotational vibrational energy levels in many organic molecules. Therefore, they can sensitively detect low-frequency vibrations of crystal lattices, stretching and bending vibrations of hydrogen bonds, phonon vibrations in crystalline states, and vibrations of the macromolecular framework. Terahertz spectroscopy, with its unique penetrability and low-energy characteristics, is widely used in liquid composition analysis and material structure characterization. The thickness of the liquid sample is a key parameter affecting the accuracy of terahertz spectroscopy measurements. Different thicknesses of liquid samples lead to differences in the absorption and reflection characteristics of the spectral signal; therefore, accurately controlling and adjusting the liquid sample thickness is a core requirement in the testing process.

[0003] See the schematic diagram of an existing terahertz spectroscopy experimental system suitable for testing liquid samples. Figure 3A femtosecond laser 01 is used to emit femtosecond laser pulses 0101. A beam splitter 0201 is disposed at the output end of the femtosecond laser 01 to partially transmit the femtosecond laser pulses 0101 as pump light 0102, and partially reflect them as probe light 0103. A low-temperature gallium arsenide crystal 05 is disposed in the propagation path of the pump light 0102 to generate a primitive terahertz wave 0501. A first off-axis parabolic mirror 301, a second off-axis parabolic mirror 302, and a liquid sample cell 4 are sequentially arranged along the propagation direction of the primitive terahertz wave 0501. After the primitive terahertz wave 0501 passes through the liquid sample in the liquid sample cell 4, it generates a terahertz wave 05 carrying sample information. 02. The third off-axis parabolic reflector 303, the fourth off-axis parabolic reflector 304, and the zinc telluride crystal 06 are sequentially arranged along the propagation direction of the terahertz wave 0502 carrying sample information. The probe light 0103 passes sequentially through the first reflector 0202, the second reflector 0203, the third reflector 0204, the fourth reflector 0205, and the fifth reflector 0206, and then interacts with the terahertz wave 0502 carrying sample information on the zinc telluride crystal 06 to form polarized modulated light. The polarized modulated light passes through the quarter-wave plate 07 and then enters the Wollaston prism 08, where it is separated into ordinary O-beams with mutually perpendicular polarization directions. The ordinary light (E-ray) and extraordinary light (E-ray) are received by the balanced photodetector 09 respectively; the output of the balanced photodetector 09 is connected to the input and output of the lock-in amplifier 010, and the output of the lock-in amplifier 010 is connected to the host computer 011; the second off-axis parabolic mirror 302, the liquid sample cell 4 and the third off-axis parabolic mirror 303 form the sample testing system 200; the first mirror 0202 and the second mirror 0203 form the optical delay line 100.

[0004] In the aforementioned system, the liquid sample cell 4 is typically a container with a fixed volume. If the thickness of the liquid sample to be tested needs to be changed, a liquid sample cell 4 of a different size must be replaced. This presents significant limitations in practical applications: Firstly, frequent replacement of the liquid sample cell 4 increases the complexity of the operation process and prolongs the testing cycle, especially in batch sample testing or multi-thickness comparison experiments, where the inefficiency is even more pronounced. Secondly, each replacement of the liquid sample cell 4 requires re-calibration of the optical path and refilling of the sample, which not only increases the risk of human error but may also affect the repeatability and accuracy of the test data due to inconsistencies in the specifications of the liquid sample cell 4 and differences in assembly precision. Furthermore, the preparation and storage of a dedicated liquid sample cell 4 increases experimental costs and makes it difficult to flexibly meet the diverse thickness adjustment needs in scientific research and industrial scenarios. Utility Model Content

[0005] The purpose of this invention is to solve the calculation problem in existing terahertz spectroscopy experimental systems where the volume of the liquid sample cell is fixed and the test thickness of the liquid sample cannot be dynamically adjusted, leading to complex experimental processes and increased risks. The invention provides a terahertz spectroscopy experimental system with an adjustable liquid sample thickness device.

[0006] The design concept of this utility model is as follows: based on the existing terahertz spectroscopy experimental system suitable for liquid sample testing, the fixed volume liquid sample cell is changed to a liquid sample cell with dynamically adjustable liquid sample thickness.

[0007] To achieve the above objectives, the technical solution provided by this utility model is as follows: A terahertz spectroscopy experimental system with an adjustable liquid sample thickness device includes a terahertz spectroscopy experimental apparatus and a first off-axis parabolic mirror, a second off-axis parabolic mirror, a liquid sample cell, a third off-axis parabolic mirror, and a fourth off-axis parabolic mirror sequentially arranged on the terahertz wave test optical path of the terahertz spectroscopy experimental apparatus. Its special feature is that: It also includes a first slide rail mounted on an external fixing device; The liquid sample cell is used to store the liquid sample to be tested and to dynamically adjust the test thickness of the liquid sample. It includes a first box and a second box, both of which are cuboids. The first box is connected to an external fixing device and is located above the first slide rail. The first enclosure includes a first enclosure body and a U-shaped extended base plate. The first enclosure body has a first opening on its side. The end of one extension arm of the extended base plate connects to the bottom of the first enclosure body at the first opening, and the upper surface of the extended base plate is coplanar with the inner bottom surface of the first enclosure body. A reflector mounting hole is provided on the inner bottom surface of the first enclosure body. The extended base plate has three reflector mounting holes, one of which is located at the bottom of the extension arm connected to the first enclosure body, and the other two are located at the end and bottom of the other extension arm, respectively. All four reflector mounting holes are arranged in a 2×2 matrix. The first, second, third, and fourth off-axis parabolic mirrors are arranged to be installed, respectively. The line connecting the second and third off-axis parabolic mirrors is parallel to the first slide rail. The side of the second housing has a second opening, and the main body of the first housing is disposed inside the second housing through the second opening. The internal space enclosed by the outer side of the first housing and the inner side of the second housing constitutes a liquid sample placement space, which is located between the second and third off-axis parabolic mirrors. The second housing is mounted on the first slide rail and can reciprocate along the first slide rail to dynamically adjust the test thickness of the liquid sample located in the liquid sample placement space.

[0008] Furthermore, a sealed top cover is provided on the top of the second chamber, located above the liquid sample placement space, and the tops of the second chamber and the first chamber are flush.

[0009] Furthermore, the first off-axis parabolic mirror, the second off-axis parabolic mirror, the third off-axis parabolic mirror, and the fourth off-axis parabolic mirror are all mirrors with adjustable mirror height.

[0010] Furthermore, an overflow hole is provided on the side of the second housing near the top, and the overflow hole is connected to an external liquid recovery container through a pipe.

[0011] Furthermore, the sealing cover plate is slidably connected to the top of the side wall of the second housing via a second slide rail, allowing the sealing cover plate to reciprocate in a direction parallel to the first slide rail.

[0012] Furthermore, the terahertz spectroscopy experimental setup includes a femtosecond laser, a beam splitter, a first reflecting mirror, a second reflecting mirror, a third reflecting mirror, a fourth reflecting mirror, a fifth reflecting mirror, a low-temperature gallium arsenide crystal, a zinc telluride crystal, a quarter-wave plate, a Wollaston prism, a balanced photodetector, a lock-in amplifier, and a host computer. The beam splitter is positioned at the output end of the femtosecond laser, and the low-temperature gallium arsenide crystal is positioned in the propagation path of the pump light to generate the original terahertz wave. The first off-axis parabolic reflecting mirror, the second off-axis parabolic reflecting mirror, and the liquid sample cell are sequentially arranged along the propagation direction of the original terahertz wave. After passing through the liquid sample in the liquid sample cell, the original terahertz wave generates a sample-carrying wave. The terahertz wave carrying the sample information is arranged sequentially along the propagation direction of the third off-axis parabolic mirror, the fourth off-axis parabolic mirror, and the zinc telluride crystal. The first, second, third, fourth, and fifth mirrors, the terahertz wave carrying the sample information, and the probe light work together to form polarized modulated light on the zinc telluride crystal. The polarized modulated light passes through a quarter-wave plate and then enters a Wollaston prism. After being separated into O-light and E-light with mutually perpendicular polarization directions by the Wollaston prism, the light is received by a balanced photodetector. The output of the balanced photodetector is connected to the input and output of a lock-in amplifier, and the output of the lock-in amplifier is connected to a host computer.

[0013] Furthermore, it also includes a stepper motor for driving the second housing to move along the first slide rail, and a linear displacement sensor for real-time detection of the position of the second housing on the first slide rail; both the stepper motor and the linear displacement sensor are electrically connected to the host computer. The linear displacement sensor sends the position information of the second housing to the host computer in real time. The host computer drives the second housing to move a preset distance precisely on the first slide rail by means of the stepper motor according to the operator's instructions and the real-time position information sent by the linear displacement sensor.

[0014] Furthermore, polyethylene sealing strips or self-adhesive liquid-swellable strips are provided at the four perimeter positions of the side of the first box that forms a liquid sample placement space with the inner side of the second box. These are used to achieve dynamic sealing when the first box and the second box move relative to each other, as well as sealing between the liquid sample placement space and the sealing cover plate.

[0015] Compared with the prior art, the beneficial effects of this utility model are: 1. The terahertz spectroscopy experimental system with an adjustable liquid sample thickness device provided by this utility model allows for direct operation in the host computer to adjust the thickness of the liquid sample during the experiment. The second chamber is moved a specified preset distance, thereby precisely adjusting the thickness of the liquid sample in the liquid sample placement space to the required value without changing the liquid sample container. This improves experimental efficiency, especially in batch sample multi-thickness comparison tests. Moreover, the terahertz wave optical path does not need to be recalibrated during the liquid test thickness adjustment process, and the specification deviation problem caused by sample cell replacement is avoided. This effectively reduces errors caused by human operation and component differences, ensuring the repeatability and accuracy of test data for different thicknesses.

[0016] 2. The terahertz spectroscopy experimental system with adjustable liquid sample thickness provided by this utility model can achieve dynamic adaptation of various liquid test thicknesses through adjustable structure. It eliminates the need to prepare a sample cell of special specifications, fundamentally reducing the dependence on specific consumables and reducing the initial investment and subsequent maintenance costs of experimental equipment.

[0017] 3. The terahertz spectroscopy experimental system with adjustable liquid sample thickness provided by this utility model is equipped with a sealed top cover and an overflow hole. The sealed top cover is used to add liquid when the amount of liquid to be measured is insufficient (such as during the process of increasing the test thickness); the overflow hole is used to drain excess liquid during the process of decreasing the test thickness; the combination of the two can be adapted to various amounts of liquid to be measured.

[0018] 4. The terahertz spectroscopy experimental system with an adjustable liquid sample thickness device provided by this utility model ensures experimental accuracy through the coordinated movement of the second chamber by the host computer, linear displacement sensor and stepper motor.

[0019] 5. The terahertz spectroscopy experimental system with adjustable liquid sample thickness provided by this utility model has polyethylene sealing strips or self-adhesive liquid-expanding adhesive strips at the four perimeter positions of the side of the first box that forms a liquid sample placement space with the inner side of the second box, which effectively prevents the volatilization or leakage of the liquid sample being tested. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the liquid sample cell, the first off-axis parabolic mirror, the second off-axis parabolic mirror, the third off-axis parabolic mirror and the fourth off-axis parabolic mirror in the embodiment of the terahertz spectroscopy experimental system with adjustable liquid sample thickness of this utility model. The dashed lines represent terahertz waves. Figure 2 for Figure 1 Exploded view; Figure 3 This is a schematic diagram of an existing terahertz spectroscopy experimental system suitable for testing liquid samples. The attached figures are labeled as follows: 01-Femtosecond laser, 0101-Femtosecond laser pulse, 0102-Pump beam, 0103-Probe beam; 0201-Beam splitter, 0202-First mirror, 0203-Second mirror, 0204-Third mirror, 0205-Fourth mirror, 0206-Fifth mirror; 301-First off-axis parabolic mirror, 302-Second off-axis parabolic mirror, 303-Third off-axis parabolic mirror, 304-Fourth off-axis parabolic mirror; 4-Liquid sample cell, 41 - First housing; 4101-Mirror mounting hole; 42-Second housing; 4201-Sealed top cover; 4202-Overflow hole; 43-First slide rail; 05-Low-temperature gallium arsenide crystal; 0501-Pristine terahertz wave; 0502-Terahertz wave carrying sample information; 06-Zinc telluride crystal; 07-Quarter-wave plate; 08-Wollaston prism; 09-Balanced photodetector; 010-Lock-in amplifier; 011-Host computer; 100-Optical delay line; 200-Sample testing system. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. In this embodiment, the liquid sample to be tested is a carbon tetrachloride (CCl4) solution of benzoic acid (C6H5COOH).

[0022] First, this embodiment provides a terahertz spectroscopy experimental system with an adjustable liquid sample thickness device, see [link to documentation]. Figure 1 and Figure 2Includes a femtosecond laser 01, a beam splitter 0201, a first reflector 0202, a second reflector 0203, a third reflector 0204, a fourth reflector 0205, a fifth reflector 0206, a first off-axis parabolic reflector 301, a second off-axis parabolic reflector 302, a third off-axis parabolic reflector 303, a fourth off-axis parabolic reflector 304, a liquid sample cell 4, a low-temperature gallium arsenide crystal 05, a zinc telluride crystal 06, a quarter-wave plate 07, and a Wola The system includes a Ston prism 08, a balanced photodetector 09, a lock-in amplifier 010, a host computer 011, and a first slide rail 43 mounted on an external fixed device; a beam splitter 0201 is mounted at the output end of the femtosecond laser 01; a low-temperature gallium arsenide crystal 05 is mounted on the propagation path of the pump light 0102 to generate the original terahertz wave 0501; and a first off-axis parabolic mirror 301, a second off-axis parabolic mirror 302, and a liquid sample cell 4 are mounted along the path of the original terahertz wave 0501. The propagation directions are set sequentially. The original terahertz wave 0501 generates a terahertz wave 0502 carrying sample information after passing through the liquid sample in the liquid sample cell 4. The third off-axis parabolic reflector 303, the fourth off-axis parabolic reflector 304, and the zinc telluride crystal 06 are set sequentially along the propagation direction of the terahertz wave 0502 carrying sample information. The first reflector 0202, the second reflector 0203, the third reflector 0204, the fourth reflector 0205, and the fifth reflector 0206 are also set sequentially. The terahertz wave 0502 carrying sample information and the probe light 0103 work together to form polarization-modulated light on the zinc telluride crystal 06. The polarization-modulated light passes through a quarter-wave plate 07 and enters the Wollaston prism 08. After being separated into O-light and E-light with mutually perpendicular polarization directions by the Wollaston prism 08, they are received by the balanced photodetector 09 respectively. The output of the balanced photodetector 09 is connected to the input and output of the lock-in amplifier 010, and the output of the lock-in amplifier 010 is connected to the host computer 011.

[0023] The liquid sample cell 4 is used to store the liquid sample to be tested and to dynamically adjust the test thickness of the liquid sample. It includes a first box 41 and a second box 42, both of which are cuboids. The first box 41 is connected to an external fixing device and is located above the first slide rail 43. The first housing 41 includes a first housing body and a U-shaped extended base plate. The side of the first housing body has a first opening. The end of an extension arm of the extended base plate is connected to the bottom of the first housing body at the first opening, and the upper surface of the extended base plate is coplanar with the inner bottom surface of the first housing body. A reflector mounting hole 4101 is provided on the inner bottom surface of the first housing body. The extended base plate has three reflector mounting holes 4101, one of which is located at the bottom of the extension arm connected to the first housing body, and the other two are located at the end and bottom of the other extension arm, respectively. All four reflector mounting holes 4101 are arranged in a 2×2 matrix and are used to mount the first reflector. The system includes an off-axis parabolic mirror 301, a second off-axis parabolic mirror 302, a third off-axis parabolic mirror 303, and a fourth off-axis parabolic mirror 304. The line connecting the second off-axis parabolic mirror 302 and the third off-axis parabolic mirror 303 is parallel to the first slide rail 43. The side of the second housing 42 has a second opening, and the main body of the first housing is disposed inside the second housing 42 through the second opening. The internal space enclosed by the outer side of the main body of the first housing and the inner side of the second housing 42 constitutes a liquid sample placement space, which is located between the second off-axis parabolic mirror 302 and the third off-axis parabolic mirror 303. The second housing 42 is mounted on the first slide rail 43 and can reciprocate along the first slide rail 43 to dynamically adjust the test thickness of the liquid sample in the liquid sample placement space. The second housing 42 is also equipped with a stepper motor for driving the second housing 42 to move along the first slide rail 43 and a linear displacement sensor for real-time detection of the position of the second housing 42 on the first slide rail 43. Both the stepper motor and the linear displacement sensor are electrically connected to the host computer 011. The linear displacement sensor sends the position information of the second housing 42 to the host computer 011 in real time. According to the operator's instructions and the real-time position information sent by the linear displacement sensor, the host computer 011 drives the ball screw structure through the stepper motor to drive the second housing 42 to move precisely a preset distance on the first slide rail 43.

[0024] In this embodiment, the first off-axis parabolic reflector 301, the second off-axis parabolic reflector 302, the third off-axis parabolic reflector 303 and the fourth off-axis parabolic reflector 304 are all reflectors with adjustable mirror heights. This allows the optical path of the terahertz wave to be dynamically adjusted to the optimal position according to different thicknesses and heights of the liquid being measured.

[0025] An overflow hole 4202 is provided on the side of the second housing 42 near the top, and the overflow hole 4202 is connected to an external liquid recovery container through a pipe.

[0026] A sealing cover plate 4201 is provided on the top of the second housing 42, located above the liquid sample placement space, and the tops of the second housing 42 and the first housing 41 are flush. The sealing cover plate 4201 is slidably connected to the top of the side wall of the second housing 42 via a second slide rail, allowing the sealing cover plate 4201 to reciprocate in a direction parallel to the first slide rail 43. Polyethylene sealing strips or self-adhesive liquid-swellable strips are provided at the four perimeters of the side of the first housing 41 that forms the liquid sample placement space with the inner side of the second housing 42, to achieve dynamic sealing when the first housing 41 and the second housing 42 move relative to each other, and to seal the liquid sample placement space with the sealing cover plate 4201.

[0027] The terahertz spectroscopic characterization method for benzoic acid (C6H5COOH) in carbon tetrachloride (CCl4) solution using the aforementioned terahertz spectroscopic experimental system with adjustable liquid sample thickness includes the following steps: Step 1: Without loading the sample to be tested, turn on the terahertz spectroscopy experimental system to start the experiment and obtain the reference time-domain electric field signal E. ref (t), where E is the electric field strength, t is time, and the subscript ref represents reference. Step 2: Slide open the sealing cover plate 4201, add a preset amount of benzoic acid carbon tetrachloride solution to the liquid sample cell, and then slide close the sealing cover plate 4201. Step 3: Input the command into the host computer 011. The host computer 011 adjusts the position of the second chamber 42 to make the thickness of the benzoic acid carbon tetrachloride solution in the liquid sample placement space 1 mm, and then starts the experiment; obtain the sample time-domain electric field signal E. s1 (t), where the subscript s1 represents a liquid sample with a thickness of 1 mm. Step 4: Analyze the time-domain electric field signal E of the sample. s1 (t) and the reference time-domain electric field signal E ref Perform a Fourier transform on (t) to obtain the sample amplitude spectrum A. s1 (ω), sample phase spectrum φ s1 (ω), Reference amplitude spectrum A ref (ω), reference phase spectrum φ ref (ω); where A is the electric field amplitude, ω is the angular frequency, and φ is the phase; Step 5: Calculate the amplitude ratio function and phase difference function ; Using the amplitude ratio function and phase difference function Calculate the refractive index function of the sample to be tested ; Step 6: Utilize the refractive index function of the sample to be tested. The thickness d and amplitude ratio function of the sample to be tested Calculate the absorption coefficient function of the sample to be tested ; where c is the speed of light, d is the thickness of the liquid sample to be tested, and n r Let n be the refractive index of the reference medium in air. r =1; where ln represents the natural logarithm operation; Step 7: Plot the absorption coefficient function of the sample to be tested. The image was used to obtain the terahertz absorption spectrum (1 mm) of benzoic acid in carbon tetrachloride solution. Step 8: Based on the terahertz absorption spectrum of benzoic acid in carbon tetrachloride solution, obtain the absorption peak data of benzoic acid in carbon tetrachloride solution within the preset range, and determine whether the absorption peak data meets the requirements. If the requirements are met, the characterization test ends. If the preset requirements are not met, return to step 3 and adjust the thickness of benzoic acid in carbon tetrachloride solution sequentially by 1mm→3mm→5mm→10mm→15mm to obtain data and generate terahertz absorption spectra (1mm), terahertz absorption spectra (3mm), terahertz absorption spectra (5mm)... until the terahertz absorption spectrum meets the requirements, such as the terahertz absorption spectrum (10mm). Then stop the characterization test and take the terahertz absorption spectrum (10mm) as the final valid result of this characterization test. Although directly adjusting the thickness to the maximum (15mm) can directly obtain the most accurate terahertz absorption spectrum with almost no missing or unclear absorption peaks, this will cause a sharp increase in the amount of liquid sample used, which is easy to lead to waste. Therefore, in practical applications, the principle of saving should be followed, and the liquid volume should be characterized sequentially from small to large.

Claims

1. A terahertz spectroscopy experimental system with an adjustable liquid sample thickness device, comprising a terahertz spectroscopy experimental apparatus and a first off-axis parabolic mirror (301), a second off-axis parabolic mirror (302), a liquid sample cell (4), a third off-axis parabolic mirror (303), and a fourth off-axis parabolic mirror (304) sequentially arranged on the terahertz wave test optical path of the terahertz spectroscopy experimental apparatus, characterized in that: It also includes a first slide rail (43) mounted on an external fixing device; The liquid sample pool (4) is used to store the liquid sample to be tested and to dynamically adjust the test thickness of the liquid sample. It includes a first box (41) and a second box (42), both of which are cuboids. The first box (41) is connected to an external fixing device and is located above the first slide rail (43). The first housing (41) includes a first housing body and a U-shaped extended base plate. The side of the first housing body has a first opening. The end of an extension arm of the extended base plate is connected to the bottom of the first housing body at the first opening, and the upper surface of the extended base plate is coplanar with the inner bottom surface of the first housing body. A reflector mounting hole (4101) is provided on the inner bottom surface of the first housing body. Three reflector mounting holes (4101) are provided on the extended base plate, one of which is located at the bottom of the extension arm connected to the first housing body, and the other two are located at the end and bottom of the other extension arm, respectively. All four reflector mounting holes (4101) are arranged in a 2×2 matrix and are used to install the first off-axis parabola. The first box (42) has a second off-axis parabolic mirror (301), a second off-axis parabolic mirror (302), a third off-axis parabolic mirror (303), and a fourth off-axis parabolic mirror (304). The line connecting the second off-axis parabolic mirror (302) and the third off-axis parabolic mirror (303) is parallel to the first slide rail (43). The second box (42) has a second opening on its side, and the first box body is set inside the second box (42) through the second opening. The internal space enclosed by the outer side of the first box body and the inner side of the second box (42) constitutes a liquid sample placement space, and the liquid sample placement space is located between the second off-axis parabolic mirror (302) and the third off-axis parabolic mirror (303). The second housing (42) is mounted on the first slide rail (43) and can reciprocate along the first slide rail (43) to dynamically adjust the test thickness of the liquid sample located in the liquid sample placement space.

2. The terahertz spectroscopy experimental system with an adjustable liquid sample thickness device according to claim 1, characterized in that: The top of the second box (42) is provided with a sealed top cover plate (4201) located above the liquid sample placement space, and the tops of the second box (42) and the first box (41) are flush.

3. The terahertz spectroscopy experimental system with an adjustable liquid sample thickness device according to claim 2, characterized in that: The first off-axis parabolic reflector (301), the second off-axis parabolic reflector (302), the third off-axis parabolic reflector (303) and the fourth off-axis parabolic reflector (304) are all reflectors with adjustable mirror height.

4. The terahertz spectroscopy experimental system with an adjustable liquid sample thickness device according to claim 3, characterized in that: An overflow hole (4202) is provided on the side of the second housing (42) near the top, and the overflow hole (4202) is connected to an external liquid recovery container through a pipe.

5. The terahertz spectroscopy experimental system with an adjustable liquid sample thickness device according to claim 4, characterized in that: The sealing cover plate (4201) is slidably connected to the top of the side wall of the second box (42) via a second slide rail, so that the sealing cover plate (4201) can reciprocate in a direction parallel to the first slide rail (43).

6. The terahertz spectroscopy experimental system with an adjustable liquid sample thickness device according to claim 5, characterized in that: The terahertz spectroscopy experimental setup includes a femtosecond laser (01), a beam splitter (0201), a first reflector (0202), a second reflector (0203), a third reflector (0204), a fourth reflector (0205), a fifth reflector (0206), a low-temperature gallium arsenide crystal (05), a zinc telluride crystal (06), a quarter-wave plate (07), a Wollaston prism (08), a balanced photodetector (09), a lock-in amplifier (010), and a host computer (011). The beam splitter (0201) is positioned at the output end of the femtosecond laser (01), and the low-temperature gallium arsenide crystal (05) is positioned in the propagation path of the pump light (0102) to generate the original terahertz wave (0501). The first off-axis parabolic mirror (301), the second off-axis parabolic mirror (302), and the liquid sample cell (4) are sequentially arranged along the propagation direction of the original terahertz wave (0501). After the original terahertz wave (0501) passes through the liquid sample in the liquid sample cell (4), A terahertz wave (0502) carrying sample information is generated. The third off-axis parabolic mirror (303), the fourth off-axis parabolic mirror (304), and the zinc telluride crystal (06) are arranged sequentially along the propagation direction of the terahertz wave (0502) carrying sample information. The first mirror (0202), the second mirror (0203), the third mirror (0204), the fourth mirror (0205), the fifth mirror (0206), and the terahertz wave (0502) carrying sample information are generated. The detector light (0103) interacts with the zinc telluride crystal (06) to form polarized modulated light. The polarized modulated light passes through a quarter-wave plate (07) and then enters a Wollaston prism (08). After being separated into O-light and E-light with mutually perpendicular polarization directions by the Wollaston prism (08), the light is received by a balanced photodetector (09). The output of the balanced photodetector (09) is connected to the input and output of a lock-in amplifier (010), and the output of the lock-in amplifier (010) is connected to a host computer (011).

7. The terahertz spectroscopy experimental system with an adjustable liquid sample thickness device according to claim 6, characterized in that: It also includes a stepper motor for driving the second housing (42) to move along the first slide rail (43), and a linear displacement sensor for real-time detection of the position of the second housing (42) on the first slide rail (43); the stepper motor and the linear displacement sensor are both electrically connected to the host computer (011). The linear displacement sensor sends the position information of the second housing (42) to the host computer (011) in real time. The host computer (011) drives the second housing (42) to move a preset distance precisely on the first slide rail (43) through the stepper motor according to the operator's instructions and the real-time position information sent by the linear displacement sensor.

8. The terahertz spectroscopy experimental system with an adjustable liquid sample thickness device according to claim 7, characterized in that: Polyethylene sealing strips or self-adhesive liquid-expanding strips are provided on the four perimeters of the side of the first box (41) that form a liquid sample placement space with the inner side of the second box (42) to achieve dynamic sealing when the first box (41) and the second box (42) move relative to each other, and sealing between the liquid sample placement space and the sealing cover plate (4201).

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