High-resolution near-field terahertz time-domain spectroscopy system and high-precision tomography method

Abstract

The application provides a high-resolution near-field terahertz time-domain spectroscopy system and a high-precision tomography method, which comprises: a first terahertz source and a second terahertz source for generating a first terahertz pulse and a second terahertz pulse under the triggering of a first pulsed laser and a second pulsed laser respectively; a terahertz detector for receiving a third terahertz pulse and a fourth terahertz pulse generated by the radiation of a sample under the triggering of a third pulsed laser; the third terahertz pulse and the fourth terahertz pulse are generated by the radiation of the sample to the first terahertz pulse and the second terahertz pulse respectively; a pulsed laser light path for transmitting the first pulsed laser, the second pulsed laser and the third pulsed laser; the distance between the sample and the first terahertz source, the distance between the sample and the second terahertz source and the distance between the sample and the terahertz detector are all less than the terahertz wavelength. The application simultaneously utilizes near-field radiation technology and near-field detection technology to improve the resolution of the system and reduce the terahertz transmission loss.

Description

Technical Field

[0001] This application relates to the field of terahertz imaging technology, specifically to a high-resolution near-field terahertz time-domain spectroscopy system and a high-precision tomographic imaging method. Background Technology

[0002] The terahertz band represents a special segment of the electromagnetic spectrum, connecting the microwave and infrared bands. Its frequencies typically range from 0.1 to 10.0 THz (1 THz = 10¹² Hz corresponds to an electromagnetic wavelength of 0.3 mm, or 1 picosecond in the time domain). Terahertz frequencies are characterized by their wide bandwidth, low photon energy, superior spectral resolution, strong coherence, and good bio-electromagnetic safety, thus playing a vital role in national development, public welfare, and scientific research. In particular, terahertz time-domain spectroscopy (THz-TDS) technology is widely used in medical imaging, security systems, semiconductors, magnetism, and other basic scientific research, and typically relies on terahertz time-domain spectroscopy systems (hereinafter referred to as THz-TDS systems).

[0003] Based on the relationship between the propagation direction of pulsed THz radiation and the position of the sample under test, THz-TDS systems can be classified into transmission and reflection systems; based on the distance between the sample under test and the terahertz source and detector, THz-TDS systems can be classified into near-field and far-field systems. Existing THz-TDS systems are diverse, each with its own advantages and disadvantages.

[0004] For example, patent application CN202110521855.9 discloses a terahertz dual-mode imaging system and method based on time-domain spectroscopy. This patent provides a terahertz dual-mode imaging system capable of both transmission-type far-field and transmission-type near-field detection. However, this patent uses transmission-type far-field radiation, which cannot avoid losses caused by the far-field optical path, and the system is complex and has low resolution; furthermore, this scheme only emphasizes imaging and cannot be used to analyze other electromagnetic properties of thin film resistivity. German patent application DE 102009000823.3 discloses a scheme for transmission-type far-field radiation and near-field detection, but this scheme cannot completely overcome the shortcomings of low resolution in time-domain spectroscopy systems.

[0005] For example, the non-patent literature Ghost spintronic THz-emitter-array microscope[J](Chen SC, Feng Z, Li J, et al. Light: Science & Applications, 2020, 9(1): 1-9.) discloses an imaging method of transmission-type near-field radiation and far-field detection. This method uses a spin terahertz source close to the sample for transmission imaging, but it cannot achieve reflection imaging, resulting in insufficient analytical capability for sample surface morphology. Secondly, this method uses a far-field single-pixel detector for detection, which has relatively lower accuracy and resolution compared to near-field detection. In addition, this method uses multiple DMD devices, which are difficult to debug. Although it saves the cost of mechanical scanning displacement stage, it also reduces the stability of the optical path, and high-resolution DMD devices are also very expensive.

[0006] In summary, the resolution of existing THz-TDS systems needs improvement. Although the resolution can be improved by replacing components, the cost is very high.

[0007] <References>

[0008] [1]SEIFERT T, et al. Nature Photonics, 2016, 10(7): 483-488.

[0009] [2] Wu Q, Zhang X C. Free-space electro-optic sampling of terahertzbeams[J]. Applied Physics Letters, 1995, 67(24): 3523-3525.

[0010] [3]Chen SC, Feng Z, Li J, et al. Ghost spintronic THz-emitter-arraymicroscope[J]. Light: Science & Applications, 2020, 9(1): 1-9.

[0011] [4] Li Z, et al. Cell proliferation, 2020, 53(4): e12788. Summary of the Invention

[0012] To improve the resolution of terahertz time-domain spectroscopy systems and reduce terahertz transmission losses, this application provides a high-resolution near-field terahertz time-domain spectroscopy system, comprising:

[0013] The first terahertz source is used to generate the first terahertz pulse under the triggering of the first pulse laser.

[0014] The second terahertz source is used to generate a second terahertz pulse when triggered by the second pulse laser.

[0015] A terahertz detector is used to receive a third terahertz pulse and a fourth terahertz pulse when triggered by a third pulse laser; the third terahertz pulse and the fourth terahertz pulse are generated by the sample under test radiating the first terahertz pulse and the second terahertz pulse, respectively.

[0016] A pulsed laser optical path is used to transmit the first pulsed laser, the second pulsed laser, and the third pulsed laser to the first terahertz source, the second terahertz source, and the terahertz detector, respectively.

[0017] Wherein, the distance between the sample to be tested and the first terahertz source, the distance between the sample to be tested and the second terahertz source, and the distance between the sample to be tested and the terahertz detector are all less than the terahertz wavelength.

[0018] In one embodiment, the second terahertz source is the first probe on a near-field terahertz dual-path probe, and the first probe is connected to a DC power supply.

[0019] The terahertz detector is the second probe on the near-field terahertz dual-path probe.

[0020] In one embodiment, the third terahertz pulse is generated by the transmission of the first terahertz pulse through the sample under test; the fourth terahertz pulse is generated by the reflection of the second terahertz pulse through the sample under test.

[0021] In one embodiment, the high-resolution near-field terahertz time-domain spectroscopy system further includes a pulsed laser;

[0022] The pulsed laser optical path includes:

[0023] An optical beam splitter is used to divide the pulsed laser generated by the pulsed laser into a first pulsed laser, a second pulsed laser, and a third pulsed laser.

[0024] A transmission-type terahertz excitation optical path is used to transmit the first pulse laser;

[0025] A reflective terahertz excitation optical path is used to transmit the second pulse laser;

[0026] The terahertz detection excitation optical path is used to transmit the third pulse laser.

[0027] In one embodiment, the transmissive terahertz excitation optical path comprises a beam expander, a reflector, a parabolic mirror, and a lens.

[0028] In one embodiment, the high-resolution near-field terahertz time-domain spectroscopy system further includes:

[0029] A current amplification circuit, connected to the terahertz detector, is used to amplify the third terahertz pulse and the fourth terahertz pulse received by the terahertz detector;

[0030] A data processing system is used to generate terahertz time-domain spectra and / or terahertz frequency-domain spectra based on the third and fourth terahertz pulses transmitted by the current amplification circuit.

[0031] In one embodiment, the high-resolution near-field terahertz time-domain spectroscopy system further includes:

[0032] A sample holder is used to support the first terahertz source and the sample to be tested in close contact with it; wherein, the first terahertz source is a spin-electron terahertz source;

[0033] The displacement stage is used to move the sample holder horizontally, thereby driving the spin electron terahertz source and the sample to be tested in close contact with it to move synchronously.

[0034] In one embodiment, the high-resolution near-field terahertz time-domain spectroscopy system further includes:

[0035] A sample holder is used to hold the sample to be tested;

[0036] A displacement stage is used to move the sample holder horizontally, thereby causing the sample to be tested to move synchronously.

[0037] On the other hand, this application also provides a high-precision tomographic imaging method, applicable to any high-resolution near-field terahertz time-domain spectroscopy system provided in this application, the method comprising:

[0038] Multiple fourth terahertz pulses are generated by the reflection of the second terahertz pulse received by the terahertz detector through a multilayer sample.

[0039] The correspondence between the fourth terahertz pulse and each layer of the multilayer sample is determined based on the reception time and amplitude.

[0040] The terahertz time-domain spectrum and / or terahertz frequency-domain spectrum generated by the fourth terahertz pulse corresponding to each layer of the multilayer sample are analyzed to obtain the tomographic image of the multilayer sample.

[0041] In one embodiment, the high-precision tomographic imaging method further includes:

[0042] Obtain the distance between the location in the multilayer sample that needs to be imaged and the surface of the multilayer sample;

[0043] Adjust the displacement of the delay line on the optical path transmitting the third pulse laser according to the distance;

[0044] The terahertz detector is triggered by the third pulse laser, so that the terahertz detector receives the fourth terahertz pulse corresponding to the position to be imaged.

[0045] The terahertz time-domain spectrum and / or terahertz frequency-domain spectrum generated by the fourth terahertz pulse corresponding to the location to be imaged are analyzed to obtain the image of the location to be imaged.

[0046] This application controls the distances between the sample under test and the terahertz radiation source, as well as the distances between the sample under test and the terahertz detector, to be less than the terahertz wavelength. This allows for simultaneous improvement of system resolution and reduction of terahertz transmission loss using near-field radiation and near-field detection techniques. Furthermore, this application uses a dual-path near-field terahertz probe as both a terahertz detector and a terahertz radiation source, combining the characteristics of both transmission and reflection propagation paths. Additionally, a uniform spin-electron terahertz source can be employed, utilizing its uniform component distribution to stably emit terahertz pulses. This scheme combines the advantages of high resolution, simple structure, and low cost. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 A schematic diagram of the high-resolution near-field terahertz time-domain spectroscopic system provided in this application.

[0049] Figure 2 Another schematic diagram of the high-resolution near-field terahertz time-domain spectroscopic system provided in this application.

[0050] Figure 3 Another schematic diagram of the high-resolution near-field terahertz time-domain spectroscopic system provided in this application.

[0051] Figure 4 Another schematic diagram of the high-resolution near-field terahertz time-domain spectroscopic system provided in this application.

[0052] Figure 5 Another schematic diagram of the high-resolution near-field terahertz time-domain spectroscopic system provided in this application.

[0053] Figure 6 This is a schematic diagram of a multilayer sample and its corresponding reflection waveform.

[0054] Figure 7 This is a schematic diagram of the high-precision tomographic imaging method provided in this application.

[0055] Figure 8 Another schematic diagram of the high-precision tomographic imaging method provided in this application.

[0056] Icon labels:

[0057] 1, 1', 2 - Terahertz source; 3 - Terahertz detector; 4 - Pulsed laser optical path; 41, 42, 43, 71 - Pulsed laser; 5 - Sample to be tested; 5' - Multilayer sample; 51' - Multilayer sample surface; 52' - Position to be imaged; 6 - Near-field terahertz dual-path probe; 61, 62 - Probes; 63, 64 - Coaxial cable; 7 - Pulsed laser; 8 - Beam expander; 9 - Current amplifier circuit; 10 - Data processing system; 11 - DC regulated power supply; 12, 12' - Sample holder; 13, 13' - Displacement stage; BS1, BS2 - Beam splitter; M1~M11 - Mirror; M12 - High-reflectivity coated right-angle prism mirror; M13, M15 - Linear coated polarizer; M14 - Waveplate; F1~F3 - Lens; P1 - Parabolic mirror; s1 - Second terahertz pulse; s2 - Fourth terahertz pulse. Detailed Implementation

[0058] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0059] This application provides a high-resolution near-field terahertz time-domain spectroscopy system, such as Figure 1 As shown, the system consists of a first terahertz source 1, a second terahertz source 2, a terahertz detector 3, and a pulsed laser optical path 4. Figure 1 The image shows a scenario where the high-resolution near-field terahertz time-domain spectroscopy system is used to detect sample 5. In this scenario, the system can satisfy the following conditions: the distances between sample 5 and the first terahertz source 1, the distance between sample 5 and the second terahertz source 2, and the distance between sample 5 and the terahertz detector 3 are all less than the terahertz wavelength, with a typical distance of less than 3 mm at 0.1 THz. It should be noted that all "distances" here refer to... Figure 1The distance along the z-direction. Therefore, it can be seen that the high-resolution near-field terahertz time-domain spectroscopic system of this application simultaneously utilizes near-field radiation technology and near-field detection technology.

[0060] Specifically, regarding the realization of near-field radiation, the pulsed laser optical path 4 transmits pulsed laser 41 and pulsed laser 42. On one hand, pulsed laser 41 is focused by a lens onto the first terahertz source 1; the first terahertz source 1 generates a first terahertz pulse under the triggering of pulsed laser 41; the first terahertz pulse radiation penetrates the sample under test 5, realizing near-field radiation. The first terahertz pulse is transmitted in the sample under test 5, generating a corresponding radiation pulse.

[0061] On the other hand, the pulsed laser 42 is focused by a lens onto the second terahertz source 2; the second terahertz source 2 generates a second terahertz pulse under the triggering of the pulsed laser 42; the second terahertz pulse radiation penetrates the sample under test 5, realizing near-field radiation. The second terahertz pulse is transmitted and reflected by the sample under test 5, and generates a corresponding radiation pulse.

[0062] Regarding the near-field detection, pulsed laser path 4 transmits pulsed laser 43, which is focused onto terahertz detector 3. Triggered by pulsed laser 43, terahertz detector 3 receives the radiation pulse corresponding to the sample under test, thus achieving near-field detection. Subsequently, the radiation pulses received by terahertz detector 3 are analyzed and processed to obtain the corresponding terahertz time-domain spectrum and / or terahertz frequency-domain spectrum.

[0063] This application controls the distance between the sample under test and the terahertz radiation source, as well as the distance between the sample under test and the terahertz detector, to be less than the terahertz wavelength. This allows for the simultaneous use of near-field radiation technology and near-field detection technology to improve the system's resolution and reduce terahertz transmission loss.

[0064] In one embodiment, when the relative positions of the first terahertz source 1, the second terahertz source 2, and the terahertz detector 3 are... Figure 1 In the setup shown, the terahertz detector 3 can only receive the radiation pulse generated by the transmission of the first terahertz pulse through the sample 5 under test, and the radiation pulse generated by the reflection of the second terahertz pulse through the sample 5 under test. For ease of distinction, this application refers to the radiation pulse generated by the transmission of the first terahertz pulse through the sample 5 under test as the third terahertz pulse. The radiation pulse generated by the reflection of the second terahertz pulse through the sample 5 under test is referred to as the fourth terahertz pulse.

[0065] At this point, the same terahertz detector 3 can receive both the third and fourth terahertz pulses, enabling the high-resolution near-field terahertz time-domain spectroscopy system of this application to simultaneously achieve transmission-type near-field radiation, reflection-type near-field radiation, and near-field detection, thus reducing the time cost of spectral detection. Since the two radiation pulses received by the terahertz detector 3 are received at different times, subsequent analysis can distinguish between the third and fourth terahertz pulses based on their reception times, or by the pulse widths of their time-domain waveforms.

[0066] In one embodiment, such as Figure 2 As shown, the second terahertz source 3 is the first probe 61 on a near-field terahertz dual-path probe 6, and the probe 61 is connected to a DC power supply.

[0067] Terahertz detector 3 is the second probe 62 on the near-field terahertz dual-path probe 6.

[0068] Specifically, the two probes of the near-field terahertz dual-path probe 6 are identical, both being near-field terahertz probes, and both probes can be connected to a coaxial cable. The two probes of the near-field terahertz dual-path probe have the following characteristics: in power-on mode, the probes can emit terahertz pulses; in non-power-on mode, they can be connected to an amplifier to detect radiated pulses.

[0069] This embodiment utilizes the above characteristics to power one of the probes 61 of the near-field terahertz dual-path probe 6 via a coaxial cable 63 (e.g., using...). Figure 3 The DC regulated power supply 11 shown is used to power the probe 62, which serves as a second terahertz source 2 capable of emitting terahertz pulses. The other probe 62 is not powered and serves as a terahertz detector 3 capable of detecting radiation pulses. Probe 62 can be connected to a current amplifier via a coaxial cable 64 to amplify and output the received radiation pulses to the next stage (e.g., [example]). Figure 3 The data processing system 10 shown in the figure.

[0070] There are several options for the first terahertz source, such as nonlinear crystals, photoconductive antennas, and spintronic terahertz sources. If a spintronic terahertz source is used, improving performance may require applying... Figure 2 The bias magnetic field in the x-direction is shown.

[0071] In one embodiment, such as Figure 3 As shown, the high-resolution near-field terahertz time-domain spectroscopy system of this application also includes a pulsed laser 7; Figure 3 The diagram shows a complete schematic of the pulsed laser optical path 4. Figure 3As can be seen, the pulsed laser optical path 4 consists of optical components such as a beam splitter, beam expander, reflector, parabolic mirror, and lens. The pulsed laser optical path 4 includes three branches: a transmission-type terahertz excitation optical path, a reflection-type terahertz excitation optical path, and a terahertz detection excitation optical path, which are used to transmit the pulsed laser generated by the pulsed laser 7 to the first terahertz source 1, the second terahertz source 2, and the terahertz detector 3, respectively.

[0072] Specifically, please see Figure 3 The pulsed laser 7 generates a pulsed laser 71. Under the action of the optical beam splitter BS1, the pulsed laser 71 is split into two paths. One path is the pulsed laser 43 formed by reflection. The other path reaches the optical beam splitter BS2 and is further split into two paths, namely the pulsed laser 41 and the pulsed laser 42.

[0073] In this process, the pulsed laser 41 sequentially passes through the beam expander 8, mirror M1, parabolic mirror P1, mirror M2, and lens F1 in the transmission terahertz excitation optical path, and finally reaches the first terahertz source 1, triggering the first terahertz source 1 to generate the first terahertz pulse. The optical path for transmitting the pulsed laser 41 can be called the transmission terahertz excitation optical path.

[0074] The pulsed laser 42 passes sequentially through mirrors M3, M4, and M5 in the reflective terahertz excitation optical path and lens F2, and finally reaches the second terahertz source 2, triggering the second terahertz source 2 to generate the second terahertz pulse.

[0075] The pulsed laser 43 sequentially passes through mirrors M6, M7, M8, M9, and M10 in the terahertz detection excitation optical path, along with a coated polarizer M13, a half-wave plate M14, a linear coated polarizer M15, a mirror M11, a lens F3, and a high-reflectivity coated right-angle prism mirror M12, finally reaching the terahertz detector 3 and triggering it to detect the radiation pulse of the sample under test. The coated polarizer M13, wave plate M14, and coated polarizer M15 of this application are combined to form a high-precision laser power adjustment module, which allows for adjustment of the intensity of the pulsed laser 43 that triggers the terahertz detector 3.

[0076] In practical applications, the pulsed laser optical path can be adjusted according to requirements, including changing the type, number, and placement of optical elements in the pulsed laser optical path. Figure 3 The pulsed lasers described are merely an example provided in this application and are not intended to limit this application. The arrival times of pulsed lasers 41, 42, and 43 at the first terahertz source 1, the second terahertz source 2, and the terahertz detector 3 can also be achieved by adjusting the distances between the components in the corresponding transmission optical paths. Pulsed lasers with shorter optical path transmission distances arrive first, and pulsed lasers with longer optical path transmission distances arrive later.

[0077] In one embodiment, please continue to see Figure 3 The high-resolution near-field terahertz time-domain spectroscopy system also includes a current amplifier circuit 9 and a data processing system 10.

[0078] The current amplification circuit 9 is connected to the terahertz detector 3 and is used to amplify the third terahertz pulse and the fourth terahertz pulse received by the terahertz detector 3 and transmit them to the data processing system 10. Figure 3 The circuit uses a near-field terahertz dual-path probe 6, so the current amplification circuit 9 is connected to the probe 62 via a coaxial cable 64.

[0079] The data processing system 10 is connected to the current amplification circuit 9 and is used to generate terahertz time-domain spectra and / or terahertz frequency-domain spectra based on the third and fourth terahertz pulses transmitted by the current amplification circuit 9. Generating terahertz time-domain and / or terahertz frequency-domain spectra based on detected radiation pulses is not the focus of this application; specific implementation methods can be found in existing technologies, and will not be described in detail here.

[0080] In one embodiment, such as Figure 4 As shown, the high-resolution near-field terahertz time-domain spectroscopy system also includes a sample holder 12 and a displacement stage 13 connected to the sample holder 12.

[0081] The sample holder 12 is used to support the first terahertz source 1 and the sample 5 to be tested in close contact with it; wherein, the first terahertz source 1 is a spin-electron terahertz source 1', and in this case, to improve performance, it may be necessary to apply a pressure to the spin-electron terahertz source 1'. Figure 4 The bias magnetic field in the x-direction is shown.

[0082] The displacement stage 13 can achieve Figure 4 The movement in the xy direction (horizontal direction) is used to move the sample holder 12 in the horizontal direction, thereby driving the spin electron terahertz source 1' and the sample 5 to be tested in close contact with it to move synchronously.

[0083] The high-resolution near-field terahertz time-domain spectroscopy system in this embodiment can obtain the sample under test in... Figure 4 The two-dimensional terahertz time-domain / frequency-domain spectrum in the xy direction is shown.

[0084] This embodiment utilizes the narrow time-domain width and high bandwidth characteristics of spin-electron terahertz source radiation, which helps to improve the imaging resolution of the high-resolution near-field terahertz time-domain spectroscopy system. Furthermore, this embodiment also utilizes the uniformity of the spin-electron terahertz source thin film, ensuring that the spin-electron terahertz source 1' can stably emit pulsed THz radiation whenever the focused spot of the pulsed laser 41 moves relative to the spin-electron terahertz source 1'. Therefore, the spin-electron terahertz source 1' can also be directly connected to the displacement stage 13, replacing the function of the sample holder, thus eliminating the need for a separate sample holder 12.

[0085] In one embodiment, such as Figure 5 As shown, the high-resolution near-field terahertz time-domain spectroscopy system also includes a sample holder 12' and a displacement stage 13' connected to the sample holder 12'.

[0086] Among them, sample holder 12' is used to hold the sample 5 to be tested;

[0087] The displacement stage 13' can achieve Figure 5 The movement in the xy direction (horizontal direction) is used to move the sample holder 12' in the horizontal direction, thereby driving the sample 5 to be tested to move synchronously.

[0088] The high-resolution near-field terahertz time-domain spectroscopy system in this embodiment can obtain the sample under test in... Figure 5 The two-dimensional terahertz time-domain / frequency-domain spectrum in the xy direction is shown.

[0089] This embodiment is similar to the previous embodiment, except that it is applicable to scenarios where the first terahertz source is a terahertz source other than a spin electron terahertz source (such as a nonlinear crystal, photoconductive antenna, etc.).

[0090] It should be noted that in this embodiment, there is a certain distance between the first terahertz source 1 and the sample 5 to be tested. In order to achieve near-field radiation, it is necessary to ensure that this distance is still less than the terahertz wavelength.

[0091] On the other hand, this application also provides a high-precision tomographic imaging method applicable to any high-resolution near-field terahertz time-domain spectroscopy system provided in this application. Figure 3 The high-resolution near-field terahertz time-domain spectroscopy system shown is used as an example for illustration. Please also refer to... Figure 3 , Figure 6 and Figure 7 The method includes the following steps:

[0092] Step S701: Obtain the second terahertz pulse s1 received by the terahertz detector 3 through a multilayer sample 5' (see...) Figure 6Multiple fourth terahertz pulses s2 are generated by reflection; wherein, the multiple fourth terahertz pulses s2 are generated by reflection of second terahertz pulses s1 by different layers of the multilayer sample 5'. During detection, the multilayer sample is placed on Figure 3 The location of sample 5 to be tested can be determined.

[0093] Step S702: Determine the correspondence between the fourth terahertz pulse and each layer of the multilayer sample based on the reception time and amplitude. This mainly utilizes the different arrival times of the second terahertz pulse s1 at different layers of the multilayer sample (manifested as different delay times for each fourth terahertz pulse) and the different signal strengths of different layers (manifested as different peak amplitudes for each fourth terahertz pulse). For details, please refer to [link to relevant documentation]. Figure 6 The waveform diagram shown.

[0094] Step S703: Analyze the terahertz time-domain spectrum and / or terahertz frequency-domain spectrum generated by the fourth terahertz pulse corresponding to each layer of the multilayer sample to obtain the tomographic image of the multilayer sample.

[0095] Here, the terahertz time-domain spectrum and / or terahertz frequency-domain spectrum of each layer are generated based on the fourth terahertz pulse corresponding to different layers of the multilayer sample 5'. Then, the terahertz time-domain spectrum and / or terahertz frequency-domain spectrum of each layer are analyzed to obtain a tomographic image containing complete information of each layer of the multilayer sample.

[0096] Therefore, it can be seen that this method can obtain the sample under test. Figure 3 The tomographic terahertz time-domain / frequency-domain spectrum in the z-direction is shown.

[0097] Furthermore, please also see Figure 3 , Figure 6 and Figure 8 The high-precision tomographic imaging method further includes:

[0098] Step S801: Obtain the distance between the location to be imaged in the multilayer sample and the surface of the multilayer sample.

[0099] Specifically, assuming the location to be imaged is 51' Figure 6 The second layer from left to right (i.e., the middle layer) of the multilayer sample 5', surface 52' is the surface of the multilayer sample 5' that first receives the second terahertz pulse s1. Figure 6 The left side of the multilayer sample 5'. The distance between the position 51' to be imaged in the multilayer sample 5' and the surface 52' of the multilayer sample is d.

[0100] Step S802: Adjust the displacement of the delay line on the optical path transmitting the third pulse laser according to the distance.

[0101] Specifically, assuming the time when the fourth terahertz pulse s2 reflected from the surface 52' of the multilayer sample is received is t seconds, then when the distance between the position 51' to be imaged in the multilayer sample 5' and the surface 52' of the multilayer sample is d, the time when the fourth terahertz pulse s2 reflected from the position 51' to be imaged is received is (t+Δt) seconds. Therefore, the fourth terahertz pulse s2 reflected from the position 51' to be imaged can be detected simply by triggering the terahertz detector 3 at (t+Δt) seconds.

[0102] The delayed or advanced trigger time can be achieved by adjusting the transmission optical path of the pulsed laser 43 that triggers the terahertz detector 3, for example, along... Figure 3 The arrows indicate the direction of adjustment for the displacement Δx of mirrors M7 and M8 in the terahertz detector excitation optical path. Figure 3 Moving to the left can delay the trigger time; towards Figure 3 Moving to the right can trigger the timer earlier.

[0103] In this step, simply move reflectors M7 and M8 to the left by Δx. At the same time that the fourth terahertz pulse reflected at the position where imaging is required reaches the terahertz detector 3, the pulsed laser 43 will trigger the terahertz detector 3.

[0104] In step S803, the terahertz detector 3 is triggered by the pulsed laser 43, causing the terahertz detector 3 to receive the fourth terahertz pulse corresponding to the position to be imaged. The pulsed laser 43 is transmitted to the terahertz detector 3 along the terahertz detection excitation optical path adjusted in step S802.

[0105] Step S804: Analyze the terahertz time-domain spectrum and / or terahertz frequency-domain spectrum generated by the fourth terahertz pulse corresponding to the location to be imaged, and obtain the image of the location to be imaged.

[0106] This embodiment and Figure 7 The difference between the corresponding embodiments is that this embodiment can perform separate analysis and imaging of one layer of a multilayer sample, while Figure 7 The corresponding embodiment analyzes and images all layers of a multilayer sample. In contrast, this embodiment does not require analyzing all the fourth terahertz pulses reflected from each layer of the multilayer sample; it only needs to extract the fourth terahertz pulse corresponding to the location to be imaged, resulting in faster imaging speed.

[0107] Figure 7 and Figure 8The high-precision tomographic imaging method presented in the paper can perform high-resolution imaging (approximately 10-100 μm) of micro-nano structures and multilayer film structures. It can not only reconstruct the three-dimensional information of the internal structure of objects, such as detecting microelectromechanical systems, small drugs, and small crop seeds, but also extract the electromagnetic parameters of each layer for materials research.

[0108] It should be noted that the tomographic imaging method using the high-resolution near-field terahertz time-domain spectroscopy system of this application is not suitable for the detection of large-sized items. In fact, in addition to tomographic imaging, the high-resolution near-field terahertz time-domain spectroscopy system of this application can also be used to analyze the carrier transport, electromagnetic properties, etc. of materials.

[0109] In summary, this application, by controlling the distances between the sample under test and the terahertz radiation source, and between the sample under test and the terahertz detector, to be less than the terahertz wavelength, simultaneously utilizes near-field radiation and near-field detection techniques to improve system resolution and reduce terahertz transmission loss. Furthermore, this application uses a dual-path near-field terahertz probe as both a terahertz detector and a terahertz radiation source, combining the characteristics of both transmission and reflection propagation paths. Further, a uniform spin-electron terahertz source can be employed, utilizing its high bandwidth to improve spectral resolution and its ease of fabrication to significantly reduce the cost of the THz-TDS system. This scheme combines the advantages of high resolution, simple structure, and low cost.

[0110] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In the description of this specification, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the embodiments in this specification.

[0111] In this specification, the illustrative expressions of the terms used do not necessarily refer to the same embodiments or examples. Furthermore, those skilled in the art can combine and integrate different embodiments or examples described in this specification, as well as features of different embodiments or examples, without contradiction. The above descriptions are merely embodiments of this specification and are not intended to limit the embodiments of this specification. Various modifications and variations can be made to the embodiments of this specification by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the embodiments of this specification should be included within the scope of the claims of the embodiments of this specification.

Claims

1. A high-resolution near-field terahertz time-domain spectroscopic system, characterized in that, include: The first terahertz source is used to generate the first terahertz pulse under the triggering of the first pulse laser. A near-field terahertz dual-path probe, comprising: The first probe serves as a second terahertz source, generating a second terahertz pulse under the triggering of the second pulsed laser, and the first probe is connected to a DC power supply. The second probe, used as a terahertz detector, receives the third and fourth terahertz pulses when triggered by the third pulse laser; the third and fourth terahertz pulses are generated by the sample under test radiating the first and second terahertz pulses, respectively. A pulsed laser optical path is used to transmit the first pulsed laser, the second pulsed laser, and the third pulsed laser to the first terahertz source, the second terahertz source, and the terahertz detector, respectively. Wherein, the distance between the sample to be tested and the first terahertz source, the distance between the sample to be tested and the second terahertz source, and the distance between the sample to be tested and the terahertz detector are all less than the terahertz wavelength; The third and fourth terahertz pulses are generated by the sample under test radiating the first and second terahertz pulses, respectively, including: The third terahertz pulse is generated by the transmission of the first terahertz pulse through the sample under test; the fourth terahertz pulse is generated by the reflection of the second terahertz pulse through the sample under test.

2. The high-resolution near-field terahertz time-domain spectroscopy system according to claim 1, characterized in that, It also includes a single-pulse laser; The pulsed laser optical path includes: An optical beam splitter is used to divide the pulsed laser generated by the pulsed laser into a first pulsed laser, a second pulsed laser, and a third pulsed laser. A transmission-type terahertz excitation optical path is used to transmit the first pulse laser; A reflective terahertz excitation optical path is used to transmit the second pulse laser; The terahertz detection excitation optical path is used to transmit the third pulse laser.

3. The high-resolution near-field terahertz time-domain spectroscopy system according to claim 2, characterized in that, The transmission-type terahertz excitation optical path consists of a beam expander, a reflector, a parabolic mirror, and a lens.

4. The high-resolution near-field terahertz time-domain spectroscopic system according to any one of claims 1 to 3, characterized in that, Also includes: A current amplification circuit, connected to the terahertz detector, is used to amplify the third terahertz pulse and the fourth terahertz pulse received by the terahertz detector; A data processing system is used to generate terahertz time-domain spectra and / or terahertz frequency-domain spectra based on the third and fourth terahertz pulses transmitted by the current amplification circuit.

5. The high-resolution near-field terahertz time-domain spectroscopic system according to any one of claims 1 to 3, characterized in that, Also includes: A sample holder is used to support the first terahertz source and the sample to be tested in close contact with it; wherein, the first terahertz source is a spin-electron terahertz source; The displacement stage is used to move the sample holder horizontally, thereby driving the spin electron terahertz source and the sample to be tested in close contact with it to move synchronously.

6. The high-resolution near-field terahertz time-domain spectroscopic system according to any one of claims 1 to 3, characterized in that, Also includes: A sample holder is used to hold the sample to be tested; A displacement stage is used to move the sample holder horizontally, thereby causing the sample to be tested to move synchronously.

7. A high-precision tomographic imaging method, characterized in that, The high-resolution near-field terahertz time-domain spectroscopy system applied to any one of claims 1 to 6 comprises: Multiple fourth terahertz pulses are generated by the reflection of the second terahertz pulse received by the terahertz detector through a multi-layer sample. The correspondence between the fourth terahertz pulse and each layer of the multilayer sample is determined based on the reception time and amplitude of the fourth terahertz pulse. The terahertz time-domain spectrum and / or terahertz frequency-domain spectrum generated by the fourth terahertz pulse corresponding to each layer of the multilayer sample are analyzed to obtain the tomographic image of the multilayer sample.

8. The high-precision tomographic imaging method according to claim 7, characterized in that, Also includes: Obtain the distance between the location in the multilayer sample that needs to be imaged and the surface of the multilayer sample; Adjust the displacement of the delay line on the optical path transmitting the third pulse laser according to the distance; The terahertz detector is triggered by the third pulse laser, so that the terahertz detector receives the fourth terahertz pulse corresponding to the position to be imaged. The terahertz time-domain spectrum and / or terahertz frequency-domain spectrum generated by the fourth terahertz pulse corresponding to the location to be imaged are analyzed to obtain the image of the location to be imaged.

Images