Method and testing system for obtaining material physical parameters based on terahertz time-domain spectroscopy

Abstract

This invention discloses a method and testing system for obtaining material physical parameters based on terahertz time-domain spectroscopy. The method includes: constructing a terahertz pump-detection system; mounting a sample onto the sample holder of the terahertz pump-detection system; measuring the sample using the terahertz pump-detection system to obtain waveform data of the terahertz time-domain spectrum of the sample; fitting the waveform data of the terahertz time-domain spectrum using a formula derived from the Drude-Smith model; and obtaining various material physical parameters of the sample based on the fitting result. This method for obtaining material physical parameters based on terahertz time-domain spectroscopy eliminates the need for Fourier transform of the terahertz time-domain spectrum to obtain the terahertz frequency-domain spectrum. It directly uses the waveform data of the measured terahertz time-domain spectrum and the formula derived from the Drude-Smith model to fit and obtain the material physical parameters of the sample, simplifying data processing and facilitating the study of material properties.

Description

Technical Field

[0001] This invention relates to the field of terahertz spectroscopy, and in particular to a method and testing system for obtaining material physical parameters based on terahertz time-domain spectroscopy. Background Technology

[0002] With the rapid development of pulsed laser technology, ultrafast pump-probe has become an advanced optical measurement technique for studying the carrier dynamics in electronic and optoelectronic materials such as metals, semiconductors, oxides, low-dimensional and nanostructures. This technique primarily measures the time-domain spectrum of the transmission or reflection intensity of a material under ultrafast pump pulses, as a function of delay time, thereby obtaining information on the excitation and relaxation of carriers in the material. The Drude-Smith model, applying Poisson statistics and considering photo-induced electron backscattering or localization effects in materials, has been widely used to understand the photoconductivity behavior deviating from the conventional Drude model found in depleted metals, some narrow-band semiconductors, thin film materials on dielectric substrates, and low-dimensional and nanostructured electronic materials. However, the current Drude-Smith model can only be applied to understand the photoconductivity of materials obtained in the frequency domain. When using ultrafast pump-probe experiments to study the time-domain response characteristics of these materials, there is currently no theoretical model that considers the photo-induced electron backscattering effect in the material. Therefore, it is necessary to extend the Drude-Smith model in the frequency domain to the time domain and apply it to the study of carrier dynamics in ultrafast pump-probe systems for metal-poor, some narrowband semiconductor, low-dimensional and nanostructured electronic materials.

[0003] Currently, the complex photoconductivity of the Drude-Smith model only has an analytical expression in the frequency domain. When processing time-domain experimental data obtained through ultrafast pump-probe measurements, it is typically assumed that the relaxation of electrons in the material is an exponential decay process over time. This assumption corresponds to the conventional Drude complex photoconductivity in the frequency domain. Therefore, this theoretical model cannot be applied to understand the time-domain photoelectric response characteristics of materials that deviate from Drude photoconductivity in the frequency domain (such as depleted metals, some narrowband semiconductors, thin film materials on dielectric substrates, low-dimensional and nanostructured electronic materials, etc.). Furthermore, for time-domain data obtained from monochromatic light pump-probe measurements, the spectrum of the material's photoelectric response cannot be obtained through Fourier transform, making it impossible to process and analyze the data using the traditional frequency-domain Drude-Smith model. Therefore, there is currently no suitable theoretical model to accurately and conveniently process time-domain data obtained by ultrafast pump-probe technology, especially for material systems whose deviated from Drude photoconductivity have already been observed in the frequency domain.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] The main objective of this invention is to provide a method and testing system for obtaining material physical parameters based on terahertz time-domain spectroscopy, which can calculate material physical parameters without performing Fourier transform to obtain terahertz frequency-domain spectra.

[0006] The first aspect of this invention discloses a method for obtaining material physical parameters based on terahertz time-domain spectroscopy, the method comprising:

[0007] Construct a terahertz pump detection system;

[0008] The sample is mounted onto the sample holder of the terahertz pump detection system;

[0009] The terahertz pump-detection system is used to measure the sample to obtain waveform data of the terahertz time-domain spectrum of the sample;

[0010] Using the formula I(t) derived from the Drude-Smith model generalization = n＝0 (t)+ n＝1 (t)+I n＝2 (t) Fit the waveform data of the terahertz time-domain spectrum, wherein,

[0011]

[0012]

[0013]

[0014] I0 is the background transmitted or reflected signal intensity, A is a coefficient, γ is the full width at half maximum (FWHM), and k1 = (γ... 2 -2tτ) / 2τ 2 , erf(x) is the error function, τ is the relaxation time of the carriers in the sample, and c1 and c2 are localization factors;

[0015] Based on the fitting results, the various material physical parameters of the sample were obtained.

[0016] In an optional embodiment of the first aspect of the present invention, the sample is a low-dimensional semiconductor material, the low-dimensional semiconductor material including monolayer MoS2, monolayer hBN, monolayer WS2 and GaSb wafer.

[0017] In one optional embodiment of the first aspect of the present invention, the terahertz pump detection system is a monochromatic picosecond terahertz pump-picosecond detection system.

[0018] In an optional embodiment of the first aspect of the present invention, the monochromatic picosecond terahertz pump-picosecond detection system includes a terahertz free-electron laser device, a first off-axis parabolic mirror, a semi-transparent reflector, a pump optical path, a detection optical path, an oscilloscope, and a computer. The detection optical path sequentially includes an optical path delay device, a first off-axis parabolic mirror, a second off-axis parabolic mirror, a sample holder, a third off-axis parabolic mirror, a fourth off-axis parabolic mirror, and a terahertz wave detector. The pump optical path sequentially includes a first reflector, a second reflector, a fifth off-axis parabolic mirror, and a terahertz beam separator. The sample holder is located between the fifth off-axis parabolic mirror and the terahertz beam separator. The terahertz wave detector is connected to the oscilloscope, and the oscilloscope is connected to the computer.

[0019] In an optional embodiment of the first aspect of the invention, the method further includes, prior to measuring the sample using the terahertz pump detection system:

[0020] The optical path of the terahertz pump detection system is calibrated using visible light to ensure that the detection spot and the pump spot are focused on the sample at the same point.

[0021] In an optional embodiment of the first aspect of the present invention, the step of measuring the sample using the terahertz pump-detection system to obtain waveform data of the terahertz time-domain spectrum of the sample includes:

[0022] The terahertz pump detection system was used to measure the sample at different pump light frequencies to obtain waveform data of the terahertz time-domain spectrum of the sample at different pump light frequencies.

[0023] A second aspect of the present invention provides a testing system for acquiring material physical parameters based on terahertz time-domain spectroscopy, the testing system comprising:

[0024] A construction device for building a terahertz pump-probe system;

[0025] Mounting device for mounting samples onto the sample holder of the terahertz pump detection system;

[0026] The testing apparatus is used to measure the sample using the terahertz pump-detection system to obtain waveform data of the terahertz time-domain spectrum of the sample.

[0027] Data processing device for using the formula I(t) derived from the Drude-Smith model = n＝0 (t)+ n＝1 (t)+ n＝2 (t) Fit the waveform data of the terahertz time-domain spectrum, wherein,

[0028]

[0029]

[0030]

[0031] I0 is the background transmitted or reflected signal intensity, A is a coefficient, γ is the full width at half maximum (FWHM), and k1 = (γ... 2 -2tτ) / 2τ 2 , erf(x) is the error function, τ is the relaxation time of the carriers in the sample, and c1 and c2 are localization factors;

[0032] A data acquisition device is used to obtain various material physical parameters of the sample based on the fitting results.

[0033] In an optional embodiment of the second aspect of the present invention, the sample is a low-dimensional semiconductor material, the low-dimensional semiconductor material including monolayer MoS2, monolayer hBN, monolayer WS2 and GaSb wafers.

[0034] In an optional embodiment of the second aspect of the present invention, the terahertz pump detection system is a monochromatic picosecond terahertz pump-picosecond detection system.

[0035] In an optional embodiment of the second aspect of the present invention, the monochromatic picosecond terahertz pump-picosecond detection system includes a terahertz free-electron laser device, a first off-axis parabolic mirror, a semi-transparent reflector, a pump optical path, a detection optical path, an oscilloscope, and a computer. The detection optical path sequentially includes an optical path delay device, a first off-axis parabolic mirror, a second off-axis parabolic mirror, a sample holder, a third off-axis parabolic mirror, a fourth off-axis parabolic mirror, and a terahertz wave detector. The pump optical path sequentially includes a first reflector, a second reflector, a fifth off-axis parabolic mirror, and a terahertz beam separator. The sample holder is located between the fifth off-axis parabolic mirror and the terahertz beam separator. The terahertz wave detector is connected to the oscilloscope, and the oscilloscope is connected to the computer.

[0036] Beneficial Effects: This invention discloses a method and testing system for obtaining material physical parameters based on terahertz time-domain spectroscopy. The method includes: constructing a terahertz pump-detection system; mounting a sample onto the sample holder of the terahertz pump-detection system; measuring the sample using the terahertz pump-detection system to obtain waveform data of the terahertz time-domain spectrum of the sample; fitting the waveform data of the terahertz time-domain spectrum using a formula derived from the Drude-Smith model; and obtaining various material physical parameters of the sample based on the fitting result. This method for obtaining material physical parameters based on terahertz time-domain spectroscopy eliminates the need for Fourier transform of the terahertz time-domain spectrum to obtain the terahertz frequency-domain spectrum. It directly uses the waveform data of the measured terahertz time-domain spectrum and the formula derived from the Drude-Smith model to fit and obtain the material physical parameters of the sample, simplifying data processing and facilitating the study of material properties. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of an embodiment of the method for obtaining material physical parameters based on terahertz time-domain spectroscopy according to the present invention;

[0038] Figure 2 This is a schematic diagram of another embodiment of the terahertz pump detection system of the present invention;

[0039] Figure 3 The diagram shows the waveform relationship between the transmission signal intensity and the delay time through the GaSb wafer using the Hertz time-domain spectroscopy system of this invention at different pump frequencies, as well as the fitting curve results obtained using the extended Drude-Smith model.

[0040] Figure 4 This is a schematic diagram of an embodiment of a testing system for obtaining material physical parameters based on terahertz time-domain spectroscopy according to the present invention.

[0041] The attached icons are numbered as follows:

[0042] 10-Terahertz free-electron laser device; 20-First off-axis parabolic mirror; 30-Semi-transparent reflector; 40-Oscilloscope; 50-Computer; 60-Optical path delay device; 70-First off-axis parabolic mirror; 80-Second off-axis parabolic mirror; 90-Sample holder; 100-Third off-axis parabolic mirror; 110-Fourth off-axis parabolic mirror; 120-Terahertz wave detector; 130-First reflector; 140-Second reflector; 150-Fifth off-axis parabolic mirror; 160-Terahertz beam separator; 170-Construction device; 180-Mounting device; 190-Testing device; 200-Data processing device; 210-Data acquisition device. Detailed Implementation

[0043] This invention provides a method and testing system for obtaining material physical parameters based on terahertz time-domain spectroscopy. The terms "first," "second," "third," "fourth," etc. (if present)," in the specification, claims, and accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" or "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0044] See Figure 1 The first aspect of this invention discloses a method for obtaining material physical parameters based on terahertz time-domain spectroscopy, the method comprising:

[0045] S100, Constructing a terahertz pump detection system; see also Figure 2 For example, the terahertz pump-detection system used in this invention is a monochromatic picosecond terahertz pump-picosecond detection system. This system includes a terahertz free-electron laser device 10, a first off-axis parabolic mirror 20, a semi-transparent mirror 30, a pump optical path, a detection optical path, an oscilloscope 40, and a computer 50. The detection optical path sequentially includes an optical path delay device 60, a first off-axis parabolic mirror 70, a second off-axis parabolic mirror 80, and a sample holder 90. The system comprises a third off-axis parabolic mirror 100, a fourth off-axis parabolic mirror 110, and a terahertz wave detector 120. The pump optical path sequentially includes a first reflector 130, a second reflector 140, a fifth off-axis parabolic mirror 150, and a terahertz beam separator 160. The sample holder 90 is located between the fifth off-axis parabolic mirror 150 and the terahertz beam separator 160. The terahertz wave detector 120 is connected to the oscilloscope 40, and the oscilloscope 40 is connected to the computer 50.

[0046] S200. The sample is mounted onto the sample holder of the terahertz pump detection system. In this embodiment, the sample is a low-dimensional semiconductor material, which includes monolayer MoS2, monolayer hBN, monolayer WS2, and GaSb wafers.

[0047] S300. The sample is measured using the terahertz pump-detection system to obtain waveform data of the terahertz time-domain spectrum of the sample; and before the measurement of the sample using the terahertz pump-detection system, the optical path of the terahertz pump-detection system is calibrated using visible light to ensure that the detection spot and the pump spot are focused on the sample at the same point.

[0048] In this step, in order to conduct a more detailed study of the sample, the measurement of the sample using the terahertz pump detection system to obtain the waveform data of the terahertz time-domain spectrum of the sample includes: measuring the sample using the terahertz pump detection system under different pump light frequencies, different temperatures, or different magnetic fields to obtain the waveform data of the terahertz time-domain spectrum of the sample under different pump light frequencies, different temperatures, and different magnetic fields respectively;

[0049] S400. Using the formula I(t) derived from the Drude-Smith model generalization, n＝0 (t)+ n＝1 (t)+I n＝2 (t) Fit the waveform data of the terahertz time-domain spectrum, wherein,

[0050]

[0051]

[0052]

[0053] I0 is the background transmitted or reflected signal intensity, A is a coefficient, γ is the full width at half maximum (FWHM), and k1 = (γ... 2 -2tτ) / 2τ 2 , erf(x) is the error function, τ is the relaxation time of the carriers in the sample, and c1 and c2 are localization factors;

[0054] Specifically, the above formula is derived from the Drude-Smith model. In the presence of photoinduced electron backscattering, similar to the Poisson-distributed current response function proposed by Smith in 2001, the photoelectric response function S(t) of the electronic material sample to the pump light can be expressed as:

[0055]

[0056] Where the coefficient a1 is the background at t=0, and τ is the electron relaxation time. n = [-1, 0] is the ratio of the electron velocity after the nth backscattering event to the initial velocity, and its physical meaning is: c nThe closer the value is to -1, the stronger the light-induced backscattering or localization effect; when c n When a1 = 0, it is the usual exponentially decaying relaxation; when a1 = n e e 2 / m * When the above equation is subjected to a Fourier transform, the Drude-Smith photoconductivity formula in the frequency domain can be obtained, where n e For electron concentration, m * The effective mass of an electron.

[0057] For femtosecond or picosecond pump-probe experiments, the detection or measurement system typically does not respond linearly to the pulsed pump light. It is usually assumed that the time resolution R(t) of the measurement system can be described by a Gaussian function with a full width at half maximum (FWHM) of γ.

[0058]

[0059] According to the principle of signal measurement, in ultrafast pump-probe measurement, the experimentally measured response function I(t) is the convolution of R(t) and S(t):

[0060] I(t)=∫R(tt′)S(t′)dt′ (3)

[0061] Combining equations (1) and (3), we can obtain:

[0062] I(t)=I n＝0 (t)+I n＝1 (t)+I n＝2 (t)+… (4)

[0063] in:

[0064]

[0065] This is a well-known result obtained without light-induced backscattering, where I0 is the intensity of the background transmitted or reflected signal, A is a coefficient, and k1 = (γ 2 -2tτ) / 2τ 2 , erf(x) is the error function. In equation (4), I n＝1 (t) and I n＝2 (t) comes from the contributions of the first and second backscattering events in the Drude-Smith model, respectively, and is expressed by the following equations:

[0066]

[0067]

[0068] For the Drude-Smith model, considering only the first backscattering effect, the frequency domain Drude-Smith model and experimental results are usually in good agreement. Therefore, in the generalized Drude-Smith formula (4), only n=1 and n=2 are considered. This model can be used to understand and explain the modified electron decay or relaxation process in the material sample. This formula shows that when there is photoinduced electron backscattering or localization effect, the transmission or reflection intensity in the ultrafast pump-probe experiment is also weakened, which is consistent with the basic physical law. When the time domain data obtained by ultrafast pump-probe measurement of materials is fitted using the above-mentioned generalized Drude-Smith model, important parameters such as γ, relaxation time τ of charge carriers in the sample, localization factors c1 and c2, which can be used to represent the time resolution of the measurement system, can be obtained, thereby gaining a deeper understanding of the experimental data of the sample under ultrafast pump-probe and analyzing the basic physical properties of the material.

[0069] S500. Based on the fitting results, obtain the various material physical parameters of the sample. The purpose of this invention is to extend the frequency domain Drude-Smith model to the time domain, enabling it to quickly and directly process time-domain experimental data obtained by ultrafast pump-probe technology. The extended Drude-Smith model can not only handle broadband optical pump-probe scenarios, but is also particularly suitable for handling single-frequency optical pump-probe scenarios (where the spectral information obtained by performing Fourier transform on the time-domain signal is limited). By fitting the time-domain experimental data obtained through ultrafast pump-probe measurements with this model, the basic physical parameters of the material (such as relaxation time and electron localization factor) and the time response of measuring instruments can be determined more accurately.

[0070] In summary, the entire process of the method described above in this invention can be summarized as follows:

[0071] 1. Construct the experimental optical path of the terahertz pump-detection system and calibrate it before the experiment. The monochromatic picosecond terahertz pump-terahertz detection transmission optical path constructed in this invention is as follows: Figure 2 As shown (other commonly used ultrafast optical pump-terahertz probe optical paths are also applicable to this invention);

[0072] 2. The sample to be tested (such as monolayer MoS2, monolayer hBN, monolayer WS2, GaSb wafers and other semiconductors and low-dimensional materials) is mounted on the sample holder. First, the optical path is calibrated using visible light to ensure that the probe spot and the pump spot are focused on the sample to be measured at the same point.

[0073] 3. Pump-probe experimental measurement: The optical pumping conditions can be changed by altering the pump light frequency or power. In addition, temperature and magnetic field tests can be performed on the sample.

[0074] 4. The experimental data measured in step 3 is the time-domain probe light signal. The variation of the signal measured with the delay time is observed under different pump light frequencies (different power, or different temperatures or magnetic fields).

[0075] 5. Subsequently, the obtained time-domain signal was fitted using the extended Drude-Smith model described above. That is, the parameters such as I0, A, τ, γ, c1, and c2 in the extended Drude-Smith model were adjusted to make the curve obtained by the model the same as the experimental data. In this way, important parameters such as the time resolution γ of the measurement system, the relaxation time τ of the carriers in the sample, and the localization factors c1 and c2 were extracted. The data obtained under different conditions (pump light frequency, power, temperature, magnetic field, etc.) were processed separately to further analyze the influence of pump light frequency (or power, temperature, magnetic field, etc.).

[0076] Application Example: Based on the Terahertz Free Electron Laser Facility (CTFEL) of the China Academy of Engineering Physics, a monochromatic picosecond terahertz pump-picosecond detection system was built using the picosecond pulse width terahertz micropulse structure provided by the facility (see [link to application example]). Figure 2 Pump-probe transmission experiments were conducted on high-mobility n-type GaSb wafers at 1.2 THz (10 W), 1.6 THz (10 W), and 2.4 THz (25 W) in free space and at room temperature. The band gap of the n-type GaSb sample used was approximately 0.7 eV, much greater than the energy of terahertz photons (1 THz = 4.1 meV), therefore terahertz irradiation did not generate photocurrents in the sample. The raw data results of the pump-probe experiments are as follows: Figure 3 As shown in the wavy curve, it can be seen that the THz transmission signal of the sample is very weak when pumped at 1.2 THz; as the terahertz pump frequency increases, the excitation-decrease behavior of the sample's transmission response becomes more obvious.

[0077] The generalized Drude-Smith model was used to fit the time-domain results obtained from the above experiments. The fitting results are displayed as smooth solid lines. Figure 3Without considering the electron backscattering effect (i.e., only taking the first region line with n=0), it can be seen that the fitting effect in the excitation (t<0) and peak (t=0) regions is not ideal. Therefore, by considering the generalized Drude-Smith model (i.e., the second curve with n=0 and 1 and the third curve with n=0, 1 and 2), the fitting of the excitation and peak regions can be significantly improved. The addition of the n=2 term (third curve) to the generalized Drude-Smith model has a relatively weak effect on the fitting results. Therefore, this means that when applying this model to fit the results obtained in the ultrafast pump-probe experiment, it is often only necessary to take n=0 and 1 in formula (5) to achieve a good fit. During the fitting process, we can determine important parameters such as the background transmission signal I0, coefficient A, relaxation time τ, γ which can be used to represent the time resolution of the measurement system, localization factors c1 and c2. Obtaining the relaxation time τ can further help us understand the effect of terahertz pumping on free electrons in the sample. Furthermore, when considering the photoinduced localization effects (c1 and c2), the relaxation time of free electrons in the sample also increases at the same radiation frequency. Compared to the results when only n=0 is considered, the time resolution of the measurement system becomes more accurate when introducing n=1 and n=2 terms. Moreover, as the radiation frequency increases, the localization effect of free electrons in GaSb gradually weakens (i.e., c1 and c2 gradually approach 0), which can be used to explain why no significant terahertz transmission signal was detected through the GaSb wafer at low radiation frequencies.

[0078] Experimental Summary: Depleted metals, some narrowband semiconductors, thin film materials on dielectric substrates, and low-dimensional and nanostructured electronic materials exhibit photoconductive behavior deviating from the conventional Drud formula in the frequency domain. This behavior can be described using the Drud-Smith model, which incorporates photoinduced electron backscattering or localization effects. This invention aims to study these materials in the time domain using ultrafast pump-probe technology. It derives a sample time response function based on the Drud-Smith model, which can be applied to study the carrier dynamics of these materials. By fitting the function to experimental data, more accurate material physics parameters and the time response sensitivity of the detection system can be obtained.

[0079] See Figure 4 The second aspect of the present invention provides a testing system for obtaining material physical parameters based on terahertz time-domain spectroscopy, the testing system comprising:

[0080] System construction device 170 is used to construct a terahertz pump-detection system, which is a monochromatic picosecond terahertz pump-picosecond detection system. The monochromatic picosecond terahertz pump-picosecond detection system includes a terahertz free-electron laser device, a first off-axis parabolic mirror, a semi-transparent reflector, a pump optical path, a detection optical path, an oscilloscope, and a computer. The detection optical path sequentially includes an optical path delay device, a first off-axis parabolic mirror, a second off-axis parabolic mirror, a sample holder, a third off-axis parabolic mirror, a fourth off-axis parabolic mirror, and a terahertz wave detector. The pump optical path sequentially includes a first reflector, a second reflector, a fifth off-axis parabolic mirror, and a terahertz beam separator. The sample holder is located between the fifth off-axis parabolic mirror and the terahertz beam separator. The terahertz wave detector is connected to the oscilloscope, and the oscilloscope is connected to the computer.

[0081] The sample mounting device 180 is used to mount the sample onto the sample holder of the terahertz pump detection system; the sample is a low-dimensional semiconductor material, including monolayer MoS2, monolayer hBN, monolayer WS2 and GaSb wafers.

[0082] The testing device 190 is used to measure the sample using the terahertz pump detection system to obtain waveform data of the terahertz time-domain spectrum of the sample.

[0083] Data processing device 200 is used to apply the formula I(t) = I derived from the Drude-Smith model. n＝0 (t)+I n＝1 (t)+I n＝2 (t) Fit the waveform data of the terahertz time-domain spectrum, wherein,

[0084]

[0085]

[0086]

[0087] I0 is the background transmitted or reflected signal intensity, A is a coefficient, γ is the full width at half maximum (FWHM), and k1 = (γ... 2 -2tτ) / 2τ 2 , erf(x) is the error function, τ is the relaxation time of the carriers in the sample, and c1 and c2 are localization factors;

[0088] The data acquisition device 210 is used to obtain various material physical parameters of the sample based on the fitting results.

[0089] In summary, this invention discloses a method and testing system for obtaining material physical parameters based on terahertz time-domain spectroscopy. The method includes: constructing a terahertz pump-detection system; mounting a sample onto the sample holder of the terahertz pump-detection system; measuring the sample using the terahertz pump-detection system to obtain waveform data of the terahertz time-domain spectrum of the sample; fitting the waveform data of the terahertz time-domain spectrum using a formula derived from the Drude-Smith model; and obtaining various material physical parameters of the sample based on the fitting result. This method for obtaining material physical parameters based on terahertz time-domain spectroscopy eliminates the need for Fourier transform of the terahertz time-domain spectrum to obtain the terahertz frequency-domain spectrum. It directly uses the waveform data of the measured terahertz time-domain spectrum and the formula derived from the Drude-Smith model to fit and obtain the material physical parameters of the sample, simplifying data processing and facilitating the study of material properties.

[0090] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features thereof can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for obtaining material physical parameters based on terahertz time-domain spectroscopy, characterized in that, The method includes: Construct a terahertz pump detection system; The sample is mounted onto the sample holder of the terahertz pump detection system; The terahertz pump-detection system is used to measure the sample to obtain waveform data of the terahertz time-domain spectrum of the sample; Using the formula I(t) derived from the Drude-Smith model generalization = n＝0 (t)+ n＝1 (t)+I n＝2 (t) Fit the waveform data of the terahertz time-domain spectrum, wherein, I0 is the background transmitted or reflected signal intensity, A is a coefficient, γ is the full width at half maximum (FWHM), and k1 = (γ... 2 -2tτ) / 2τ 2 , erf(x) is the error function, τ is the relaxation time of the carriers in the sample, and c1 and c2 are localization factors; Based on the fitting results, the various material physical parameters of the sample were obtained.

2. The method for obtaining material physical parameters based on terahertz time-domain spectroscopy according to claim 1, characterized in that, The sample is a low-dimensional semiconductor material, which includes monolayer MoS2, monolayer hBN, monolayer WS2, and GaSb wafers.

3. The method for obtaining material physical parameters based on terahertz time-domain spectroscopy according to claim 1, characterized in that, The terahertz pump detection system is a monochromatic picosecond terahertz pump-picosecond detection system.

4. The method for obtaining material physical parameters based on terahertz time-domain spectroscopy according to claim 3, characterized in that, The monochromatic picosecond terahertz pump-picosecond detection system includes a terahertz free-electron laser device, a first off-axis parabolic mirror, a semi-transparent reflector, a pump optical path, a detection optical path, an oscilloscope, and a computer. The detection optical path sequentially includes an optical path delay device, a first off-axis parabolic mirror, a second off-axis parabolic mirror, a sample holder, a third off-axis parabolic mirror, a fourth off-axis parabolic mirror, and a terahertz wave detector. The pump optical path sequentially includes a first reflector, a second reflector, a fifth off-axis parabolic mirror, and a terahertz beam separator. The sample holder is located between the fifth off-axis parabolic mirror and the terahertz beam separator. The terahertz wave detector is connected to the oscilloscope, and the oscilloscope is connected to the computer.

5. The method for obtaining material physical parameters based on terahertz time-domain spectroscopy according to claim 1, characterized in that, The process of measuring the sample using the terahertz pump detection system also includes: The optical path of the terahertz pump detection system is calibrated using visible light to ensure that the detection spot and the pump spot are focused on the sample at the same point.

6. The method for obtaining material physical parameters based on terahertz time-domain spectroscopy according to claim 1, characterized in that, The step of measuring the sample using the terahertz pump-detection system to obtain the waveform data of the terahertz time-domain spectrum of the sample includes: The terahertz pump detection system was used to measure the sample at different pump light frequencies to obtain waveform data of the terahertz time-domain spectrum at different pump light frequencies.

7. A testing system for acquiring material physical parameters based on terahertz time-domain spectroscopy, characterized in that, The testing system includes: A construction device for building a terahertz pump-probe system; Mounting device for mounting samples onto the sample holder of the terahertz pump detection system; The testing apparatus is used to measure the sample using the terahertz pump-detection system to obtain waveform data of the terahertz time-domain spectrum of the sample. Data processing device for using the formula I(t) derived from the Drude-Smith model generalization = n＝o (t)+ n＝1 (t)+ b＝2 (t) Fit the waveform data of the terahertz time-domain spectrum, wherein, I0 is the background transmitted or reflected signal intensity, A is a coefficient, γ is the full width at half maximum (FWHM), and k1 = (γ... 2 -2tτ) / 2τ 2 , erf(x) is the error function, τ is the relaxation time of the carriers in the sample, and c1 and c2 are localization factors; A data acquisition device is used to obtain various material physical parameters of the sample based on the fitting results.

8. The testing system for acquiring material physical parameters based on terahertz time-domain spectroscopy according to claim 7, characterized in that, The sample is a low-dimensional semiconductor material, which includes monolayer MoS2, monolayer hBN, monolayer WS2, and GaSb wafers.

9. The testing system for obtaining material physical parameters based on terahertz time-domain spectroscopy according to claim 7, characterized in that, The terahertz pump detection system is a monochromatic picosecond terahertz pump-picosecond detection system.

10. The testing system for acquiring material physical parameters based on terahertz time-domain spectroscopy according to claim 9, characterized in that, The monochromatic picosecond terahertz pump-picosecond detection system includes a terahertz free-electron laser device, a first off-axis parabolic mirror, a semi-transparent reflector, a pump optical path, a detection optical path, an oscilloscope, and a computer. The detection optical path sequentially includes an optical path delay device, a first off-axis parabolic mirror, a second off-axis parabolic mirror, a sample holder, a third off-axis parabolic mirror, a fourth off-axis parabolic mirror, and a terahertz wave detector. The pump optical path sequentially includes a first reflector, a second reflector, a fifth off-axis parabolic mirror, and a terahertz beam separator. The sample holder is located between the fifth off-axis parabolic mirror and the terahertz beam separator. The terahertz wave detector is connected to the oscilloscope, and the oscilloscope is connected to the computer.

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