A time-domain spectroscopy system that can generate and detect ultra-wideband terahertz pulses

Abstract

The application discloses a time-domain spectrum system capable of generating and detecting ultra-wideband terahertz pulses. The system comprises a laser light source, a light splitting module, an optical path adjustment coupling module, a terahertz emission module, a sample detection module and an electro-optic sampling module. After the laser pulses output by the laser light source are split, the pump light is chopped, modulated, expanded and irradiated to a spin terahertz emitter to generate ultra-wideband terahertz pulses of 0.1-10 THz. After the terahertz pulses interact with the sample through a confocal off-axis parabolic mirror, the terahertz pulses are collimated and output again. The detection light formed by light splitting is adjusted in optical path and coincides with the terahertz pulses in time and space, and is focused on an ultra-thin ZnTe crystal in the <110> crystal direction. Finally, the terahertz time-domain signal is obtained through electro-optic sampling. The system has the functions of emitting and detecting ultra-wideband terahertz pulses, and can be used not only in the fields of material detection and physicochemical analysis, but also in the precise verification of the characteristics of other terahertz sources and detection crystals.

Description

Technical Field

[0001] This invention relates to the field of broadband terahertz time-domain spectroscopy, and more particularly to the field of ultra-wideband terahertz emission and ultra-wideband terahertz detection. Background Technology

[0002] Terahertz (THz) waves typically refer to electromagnetic radiation with frequencies ranging from 0.1 THz to 10 THz. They are characterized by their transient nature, low photon energy, high transmittance, and broadband bandwidth. Terahertz waves offer high resolution, allowing for direct or indirect detection of information about matter. Because this region coincides with many fundamental resonances of materials, terahertz radiation enables fingerprint-like spectral analysis of all states of matter with high temporal and spatial resolution. Therefore, it has found numerous applications in basic research, imaging, and quality control.

[0003] To fully utilize the potential of terahertz radiation, low-pump-energy and low-cost ultrashort terahertz pulse sources are required. Most broadband terahertz emitters are driven by femtosecond laser pulses, generating the desired terahertz charge current by appropriately mixing various optical frequencies. Solid-state sources typically consist of semiconductor or dielectric structures with naturally or artificially disrupted inversion symmetry. When the incident photon energy is below the semiconductor bandgap, optical rectification results in a charge displacement that follows the intensity envelope of the incident pump pulse. For the aforementioned bandgap excitation, the response is primarily dominated by the photocurrent, which begins in a stepwise manner over time, thus the bandwidth is typically smaller than that of optical rectification. However, with very few exceptions, most semiconductors used are polar and strongly attenuate terahertz radiation around the optical phonon resonance, thereby suppressing emission in the so-called reststrahlen band located between ~1 and 15 THz.

[0004] To date, the most promising source covering the entire terahertz window is the photocurrent in transient gas plasmas. A drawback of this attractive approach is that the potential ionization process typically requires amplified laser pulses with high threshold energies on the order of 0.1 mJ. Measurable terahertz waveforms can be obtained with pump pulse energies as low as approximately 1 μJ, but these are still two to three orders of magnitude larger than those provided by low-cost femtosecond laser oscillators, and the instability of gas terahertz sources leads to difficulties in their use.

[0005] Furthermore, detecting broadband terahertz pulses is extremely important. Currently, two techniques—photoconductive and electro-optic sampling—are used to detect terahertz electric fields. In common electro-optic sampling methods, terahertz pulses and infrared laser pulses are co-transmitted through a non-centrosymmetric crystal. Due to the linear electro-optic effect, the near-infrared detection pulse senses the electric field of the terahertz pulse in the overlapping region and accumulates ellipticity. Measuring this ellipticity as a function of the delay between the terahertz and visible light pulses allows us to sample the electric field of the terahertz pulse.

[0006] For accurate electro-optic sampling and detection of monochromatic terahertz waves, the phase velocity must equal the group velocity of the near-infrared sampling pulse. However, due to velocity mismatch in commonly used zincblende crystals (such as GaP and ZnTe), this causes the signal to disappear when the near-infrared pulse sweeps through one cycle of the terahertz wave. These time walk-off effects are typically exacerbated above the Reststrahlen band.

[0007] In summary, existing femtosecond laser-driven solid-state terahertz sources have drawbacks such as system complexity, high cost, difficulty in data storage, lack of high-frequency information, and difficulty in accurately acquiring terahertz information, which cannot meet the needs for ultra-wideband strong-field terahertz sources and detection. Summary of the Invention

[0008] The purpose of this invention is to solve the above-mentioned problems existing in the prior art and to provide a time-domain spectral system that can generate and detect ultra-wideband terahertz pulses.

[0009] The specific technical solution adopted in this invention is as follows:

[0010] A time-domain spectroscopic system capable of generating and detecting ultra-wideband terahertz pulses includes a laser source, a beam splitting module, an optical path adjustment coupling module, a terahertz emission module, a sample detection module, and an electro-optic sampling module.

[0011] The laser source is used to output laser pulses with a pulse width not exceeding 35 fs;

[0012] The beam splitter module is used to split the laser pulse into a pump pulse and a probe pulse;

[0013] The terahertz emission module is used to first modulate the pump pulse through a chopper and then send it into a beam expansion system to form a collimated pump beam, which is then irradiated onto a spin terahertz emitter in the form of a three-layer heterojunction composed of a tungsten layer, a cobalt iron boron layer and a platinum layer in sequence, to generate an ultra-wideband terahertz pulse covering a continuous spectral range of 0.1-10 THz.

[0014] The sample detection module is used to introduce the ultra-wideband terahertz pulse into the confocal off-axis parabolic mirror unit, and after interacting with the sample to be tested at the focal point, it is re-collimated and output.

[0015] The optical path adjustment coupling module is used to adjust the optical path of the detection pulse so that it coincides with the terahertz pulse collimated and output by the sample detection module in time, and to focus and overlap the detection pulse and the terahertz pulse in space and synchronously irradiate the detection crystal in the electro-optic sampling module.

[0016] The electro-optic sampling module uses <110> An ultra-thin ZnTe crystal with specific crystal orientation is used as a detector crystal to acquire terahertz time-domain signals through electro-optic detection.

[0017] Preferably, the center wavelength of the laser pulse is 800~1550 nm, the pulse width is no more than 35 fs, and the repetition frequency is no less than 1 kHz.

[0018] Preferably, the beam splitting module consists of a half-wave plate and a polarizing beam splitter arranged sequentially along the optical path.

[0019] Preferably, the beam expanding system consists of a concave lens and a first convex lens arranged sequentially along the optical path.

[0020] Preferably, the spin terahertz emitter is obtained by forming a three-layer heterojunction on the surface of a SiO2 substrate by magnetron sputtering, wherein the thickness of the tungsten layer, cobalt-iron-boron layer and platinum layer in the three-layer heterojunction is 1.8~2.0 nm.

[0021] Preferably, the confocal off-axis parabolic mirror unit is composed of a first confocal off-axis parabolic mirror and a second off-axis parabolic mirror, and the focal point is used as the placement position of the sample to be tested. The ultra-wideband terahertz pulse output by the terahertz emission module interacts with the sample to be tested after being focused by the first off-axis parabolic mirror, and is then re-collimated and output by the second off-axis parabolic mirror.

[0022] Preferably, the optical path adjustment coupling module includes an optical path adjustment unit driven by a linear displacement stage, a second convex lens, and a third off-axis parabolic mirror. The detection pulse generated by the beam splitting module is first adjusted by the optical path adjustment unit, then focused by the second convex lens and passes through the light-transmitting hole on the third off-axis parabolic mirror to illuminate a designated position on the surface of the detection crystal. The terahertz pulse collimated and output by the sample detection module is focused by the third off-axis parabolic mirror and illuminated together with the detection pulse at the same position on the surface of the detection crystal.

[0023] Preferably, the electro-optic sampling module consists of a detector crystal, a third convex lens, a quarter-wave plate, a Wollaston prism, and a balanced detector arranged sequentially along the optical path.

[0024] Preferably, the thickness of the ultrathin ZnTe crystal is 100 μm.

[0025] Preferably, the time-domain spectral system is further provided with a series of mirrors for changing the optical path in order to optimize the spatial layout of the system.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1) This invention provides a time-domain spectroscopy system that can generate and detect ultra-wideband terahertz pulses. This terahertz time-domain spectroscopy system has the function of both emitting and detecting ultra-wideband terahertz pulses. Therefore, this system can not only be used in the fields of material detection and physicochemical analysis, but also for accurately verifying the emission characteristics of other terahertz sources.

[0028] 2) This invention is based on <110> Ultra-thin (100 μm thickness level) ZnTe crystals with specific crystal orientations can be used as electro-optic sampling and detection crystals. This approach can reduce terahertz phonon absorption in thick crystals, ensure broadband detection accuracy, and avoid interference from echo signals in thin crystals, thus balancing cost and detection accuracy.

[0029] 3) This invention uses a spin terahertz emitter as the terahertz source of the system. It employs a three-layer heterostructure of [tungsten|cobalt-iron-boron|platinum], exhibiting high emission efficiency and ensuring high peak electric field and single-pulse energy of the terahertz electromagnetic pulse. Furthermore, the spin terahertz emitter is unaffected by the pump light wavelength and polarization, and the polarization of the terahertz waves can be easily controlled by an external magnetic field. Moreover, since the spin terahertz emitter does not exhibit phonon absorption, with a sufficiently narrow pump light pulse width, this heterojunction can efficiently generate ultra-wideband electromagnetic radiation of 0.1-10 THz, extending the study of terahertz-matter interactions to higher frequency bands. Additionally, this spin terahertz emitter is simple to fabricate, inexpensive, and easily integrated with metasurfaces, thereby achieving more attractive radiation characteristics, which is highly conducive to commercialization. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the time-domain spectral system structure in an embodiment of the present invention;

[0031] Figure 2 The time-domain spectral signal obtained by the time-domain spectral system in this embodiment of the invention is a spin terahertz emitter pumped by a Ti:sapphire laser amplifier with a pulse width of 35 fs, a repetition frequency of 1 kHz, and a pump energy of 5.5 mJ.

[0032] Figure 3 The frequency domain spectral signal obtained by this time-domain spectral system is shown in the embodiment, when the spin terahertz emitter is pumped by a Ti:sapphire laser amplifier with a pulse width of 35 fs, a repetition frequency of 1 kHz, and a pump energy of 5.5 mJ.

[0033] The figures are labeled as follows: Laser pulse 1, First reflector 2, Half-wave plate 3, Polarizing beam splitter 4, Second reflector 5, Chopper 6, Concave lens 7, First convex lens 8, Third reflector 9, Spin terahertz emitter 10, Terahertz pulse 11, First off-axis parabolic mirror 12, Second off-axis parabolic mirror 13, Third off-axis parabolic mirror 14, Fourth reflector 15, Fifth reflector 16, Sixth reflector 17, Seventh reflector 18, Eighth reflector 19, Ninth reflector 20, Second convex lens 21, Detector crystal 22, Tenth reflector 23, Third convex lens 24, Half-wave plate 25, Wollaston prism 26, Balance detector 27, Sample under test 28. Detailed Implementation

[0034] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Technical features in various embodiments of the present invention can be combined accordingly without mutual conflict.

[0035] In the description of this invention, it should be understood that when an element is considered to be "connected" to another element, it can be a direct connection to the other element or an indirect connection, i.e., there is an intermediate element. Conversely, when an element is said to be "directly" connected to another element, there is no intermediate element.

[0036] In the description of this invention, it should be understood that the terms "first" and "second" are used only for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature.

[0037] This invention provides a time-domain spectroscopy system capable of generating and detecting ultra-wideband terahertz pulses. This system can be used to study the absorption and shielding effects of matter on terahertz pulses, and also to detect the emission performance of novel terahertz emitters and the detection performance of novel terahertz detection crystals. The specific implementation of this time-domain spectroscopy system is described in detail below.

[0038] In a preferred embodiment of the present invention, the aforementioned time-domain spectral system capable of generating and detecting ultra-wideband terahertz pulses mainly comprises a laser source, a beam splitting module, an optical path adjustment coupling module, a terahertz emission module, a sample detection module, and an electro-optic sampling module. The specific implementation methods of each module and their interrelationships are as follows:

[0039] In the time-domain spectral system of the present invention, the laser source is used to output a laser pulse 1 with a pulse width not exceeding 35 fs. The specific parameters of the laser pulse 1 can be adjusted according to actual detection requirements. Its center wavelength is preferably 800~1550 nm, the pulse width is preferably not exceeding 35 fs, and the repetition frequency is preferably not less than 1 kHz. The smaller the pulse width of the laser pulse 1, the larger the bandwidth of the subsequently generated terahertz wave. Therefore, the laser parameters can be reasonably optimized according to the bandwidth required for actual detection.

[0040] In the time-domain spectral system of the present invention, the beam splitting module is used to split the laser pulse 1 into a pump pulse and a probe pulse. As a preferred embodiment of the present invention, the beam splitting module consists of a half-wave plate 3 and a polarizing beam splitter 4 arranged sequentially along the optical path. The laser pulse 1 first passes through the half-wave plate 3 and then through the polarizing beam splitter 4, and is subsequently split into a pump pulse and a probe pulse according to the beam splitting ratio of the polarizing beam splitter 4. The pump pulse is used in conjunction with a spin terahertz emitter to generate an ultra-wideband terahertz wave, which is then loaded onto the probe crystal together with the probe pulse. The beam splitting ratio of the pump pulse and the probe pulse by the polarizing beam splitter 4 can be adjusted according to actual needs, preferably 9:1.

[0041] In the above-mentioned time-domain spectral system of the present invention, the terahertz emission module is used to first modulate the pump pulse by the chopper 6 and then send it into the beam expansion system to form a collimated pump beam, which is then irradiated onto the spin terahertz emitter 10 to generate an ultra-wideband terahertz pulse covering a continuous spectral width range of 0.1-10 THz.

[0042] It should be noted that the chopping frequency of chopper 6 can be adjusted according to actual modulation requirements, preferably 500Hz. At this chopping frequency, the system's signal-to-noise ratio and terahertz emission intensity are generally well-balanced. Furthermore, the aforementioned beam expanding system is generally composed of a combination of concave and convex lenses, and its expansion factor can be adjusted according to the actual size of the sample being tested. In a preferred embodiment of the present invention, the beam expanding system consists of a concave lens 7 and a first convex lens 8 arranged sequentially along the optical path. The focal lengths of the concave lens 7 and the first convex lens 8 are 50 mm and 100 mm, respectively. In this case, the expansion factor is 2 times, which can expand the collimated pump beam to 22 mm.

[0043] Furthermore, in this invention, a spin terahertz emitter 10 is used as the terahertz source of the system. This spin terahertz emitter 10 has a three-layer heterojunction composed of a tungsten layer, a cobalt-iron-boron layer, and a platinum layer sequentially composited. The specific thickness of the three-layer heterojunction can be adjusted according to actual needs, and its processing method can refer to existing technologies. As a preferred embodiment of this invention, the spin terahertz emitter 10 is obtained by forming a three-layer heterojunction on the surface of a SiO2 substrate using magnetron sputtering, wherein the tungsten (W) layer, cobalt-iron-boron (Co) layer, and platinum layer are composited in the three-layer heterojunction.20 Fe 60 B 20 The thickness of the tungsten (T) layer and the platinum (Pt) layer is 1.8~2.0 nm. More preferably, the spin terahertz emitter 10 can be fabricated as follows: using a 500 μm thick SiO2 substrate as the base, a 1.9 nm thick tungsten layer, a 1.9 nm thick cobalt-iron-boron (CFI) layer, and a 1.9 nm thick platinum layer are sequentially fabricated on the substrate surface by magnetron sputtering, thereby forming a three-layer heterojunction in the form of [tungsten (1.9 nm)|cobalt-iron-boron (1.9 nm)|platinum (1.9 nm)], thus completing the fabrication of the spin terahertz emitter. This 1.9 nm thick three-layer heterojunction has the highest terahertz emission efficiency, which can improve the peak electric field and single-pulse energy of the terahertz electromagnetic pulse.

[0044] This invention uses a spin terahertz emitter as a terahertz source. Since the spin terahertz emitter is unaffected by the pump light wavelength and polarization, the polarization of the terahertz waves can be easily controlled by an external magnetic field. Furthermore, because the spin terahertz emitter does not absorb phonons, this three-layer heterojunction can efficiently generate ultra-wideband electromagnetic radiation covering 0.1-10 THz with a pump light pulse width of 35 fs, extending the study of terahertz-matter interactions to higher frequency bands. Moreover, further reducing the pump light pulse width can further expand the broadband of the emitted terahertz waves.

[0045] In the above-described time-domain spectroscopy system of the present invention, the sample detection module is used to introduce the ultra-wideband terahertz pulse generated by the spin terahertz emitter 10 into the confocal off-axis parabolic mirror unit, and after interacting with the sample 28 to be tested at the focal point, it is re-collimated and output.

[0046] It should be noted that the sample 28 to be tested in the aforementioned confocal off-axis parabolic mirror unit is not an inherent component of the time-domain spectroscopy system of this invention, but rather a sample placed by the user during actual use of the system. The specific type of sample placed can be designed according to actual detection requirements and is not limited thereto. The aforementioned confocal off-axis parabolic mirror unit is generally composed of a pair of off-axis parabolic mirrors, with their focal point used to place the sample 28 to be tested. As a preferred embodiment of this invention, the aforementioned confocal off-axis parabolic mirror unit consists of a confocal first off-axis parabolic mirror 12 and a second off-axis parabolic mirror 13, i.e., the first off-axis parabolic mirror 12 and the second off-axis parabolic mirror 13 are configured with their focal points overlapping, thus this focal point can be used as the placement position for detecting the sample 28. In actual use, the sample 28 to be tested can be fixed at this focal point using an external platform or tool. The ultra-wideband terahertz pulse output by the terahertz emission module is focused by the first off-axis parabolic mirror 12 and interacts with the sample 28 under test. It is then re-collimated and output by the second off-axis parabolic mirror 13. Because this system provides ultra-wideband terahertz waves in the range of 0.1-10 THz, it can be used not only to study the absorption of terahertz pulses by matter but also to study the shielding effect of matter on terahertz pulses. This system pushes the study of matter-terahertz interactions to higher frequency bands and has enormous application prospects in material characterization and terahertz shielding material research.

[0047] In the above-described time-domain spectral system of the present invention, the optical path adjustment coupling module is used to adjust the optical path of the detection pulse generated by the above-described spectroscopic module so that it coincides with the terahertz pulse collimated and output by the above-described sample detection module in time, and then focuses and overlaps the detection pulse and the terahertz pulse in space and synchronously irradiates the detection crystal 22 in the subsequent electro-optic sampling module.

[0048] It should be noted that the optical path adjustment coupling module has two functions: firstly, it adjusts the detection pulse and the terahertz pulse in time so that they coincide and synchronously illuminate the detection crystal 22; secondly, it adjusts the detection pulse and the terahertz pulse in space so that they coincide and are collinear in space, synchronously illuminating the same excitation position on the detection crystal 22. In a preferred embodiment of the present invention, the optical path adjustment coupling module includes an optical path adjustment unit driven by a linear displacement stage, a second convex lens 21, and a third off-axis parabolic mirror 14. The optical path adjustment unit driven by the linear displacement stage is prior art and includes a series of mirrors, some of which are driven by the linear displacement stage. Mechanical movement of these mirrors changes the propagation distance of light in space, thereby precisely controlling the time when the light pulse arrives at the detection crystal 22. In this preferred embodiment, in addition to adjusting the two pulses in time through the optical path adjustment unit driven by the linear displacement stage, the second convex lens 21 and the third off-axis parabolic mirror 14 are introduced to further adjust the two pulses in space. Specifically, the third off-axis parabolic mirror 14 has a light-transmitting hole. The detection pulse generated by the beam splitting module is first adjusted by the optical path adjustment unit, and then focused by the second convex lens 21 so that it can pass through the light-transmitting hole on the third off-axis parabolic mirror 14. After the focused detection pulse passes through the light-transmitting hole on the third off-axis parabolic mirror 14, it illuminates the designated excitation position on the surface of the detection crystal 22. The terahertz pulse collimated and output by the sample detection module is also focused by the third off-axis parabolic mirror 14 and illuminated at the same excitation position on the surface of the detection crystal 22. The output directions of the focused detection pulse and the focused terahertz pulse of the third off-axis parabolic mirror 14 are collinear, so the two are also aligned in space. Therefore, the subsequent detector crystal 22 will synchronously receive the detector pulse and terahertz pulse that are aligned in time and space. The terahertz pulse carries the sample information after interacting with the sample 28. The modulated detector pulse and the terahertz pulse carrying the sample information are precisely incident on the detector crystal in time and space. The terahertz wave modulates the optical properties of the detector crystal, thereby changing the polarization state of the detector pulse passing through the crystal. This detector pulse carrying the terahertz electric field information then enters other photoelectric conversion units of the electro-optic detection module and is converted into a voltage signal that is easy to measure.

[0049] In the above-described time-domain spectral system of the present invention, the electro-optic sampling module employs... <110> An ultrathin zinc telluride (ZnTe) crystal with a specific crystal orientation is used as the detector crystal 22 to acquire terahertz time-domain signals via electro-optic detection. The specific thickness of the ultrathin ZnTe crystal can be optimized and adjusted according to actual conditions. As a preferred embodiment of the present invention, a thickness of 100 μm and a specific crystal orientation are used. <110> Using ZnTe crystals as detector crystals for electro-optic sampling, these thin ZnTe crystals can effectively reduce the phonon absorption effect of thick ZnTe crystals on terahertz waves, ensuring the accuracy of broadband detection. At the same time, they avoid the interference of echo signals generated by ultra-thin detector crystals on the detection results, and ultimately achieve reliable assurance of detection accuracy while taking into account cost control.

[0050] In addition to the detector crystal 22, the electro-optic sampling module also requires other necessary photoelectric conversion units to convert the detection pulses carrying terahertz electric field information output by the detector crystal 22 into terahertz time-domain signals in the form of electrical signals. As a preferred embodiment of the present invention, the electro-optic sampling module consists of a detector crystal 22, a third convex lens 24, a quarter-wave plate 25, a Wollaston prism 26, and a balanced detector 27 arranged sequentially along the optical path. The detection pulses pass sequentially through the quarter-wave plate 25 and the Wollaston prism 26 before being detected by the balanced detector 27, thereby acquiring the terahertz time-domain signal using the electro-optic effect of the electro-optic crystal.

[0051] It should also be noted that in the above structural description of the time-domain spectral system, the laser source, the beam splitting module, the optical path adjustment coupling module, the terahertz emission module, the sample detection module, and the electro-optic sampling module are all core functional units. However, in practical applications, a series of mirrors can be further introduced into this time-domain spectral system to convert and fold the optical path, thereby optimizing the system's spatial layout and improving the overall integration and space occupancy.

[0052] The following is a preferred embodiment of the present invention to illustrate the technical effects of the above-described time-domain spectral system.

[0053] Example

[0054] In this embodiment, the aforementioned time-domain spectral system capable of generating and detecting ultra-wideband terahertz waves is as follows: Figure 1 As shown, its overall structure and working principle are as follows:

[0055] A laser pulse 1 with a center wavelength of 800 nm, a pulse width of 35 fs, and a repetition frequency of 1 kHz is generated by a Ti:sapphire laser amplifier as the light source. After being reflected by the first reflecting mirror 2, the laser pulse 1 passes sequentially through a half-wave plate 3 and a 9:1 beam splitter 4, thereby splitting the laser beam into a pump pulse and a probe pulse. The pump pulse is input into the terahertz emission module, and the probe pulse is input into the optical path adjustment coupling module.

[0056] In the terahertz emission module, before irradiating the spin terahertz emitter 10 with a pump laser, the pump pulse output from the beam splitter 4 is refracted by the second reflector 5 and then passed through the chopper 6 with a chopping frequency of 500 Hz. Then, it is expanded to 22 mm by a double beam expansion system composed of a concave lens 7 (focal length 50 mm) and a first convex lens 8 (focal length 100 mm). This fully utilizes the pump laser energy while avoiding damage to the spin terahertz emitter, enabling it to operate stably for a long time. The expanded pump beam, after reflection by the third mirror 9, illuminates the aforementioned spin terahertz emitter 10, which is formed by magnetron sputtering a three-layer heterojunction [tungsten (1.9 nm)|cobalt-iron-boron (1.9 nm)|platinum (1.9 nm)] on a 500 μm thick SiO2 substrate. This excites the spin terahertz emitter 10 to generate an ultra-wideband terahertz pulse 11 with a continuous spectral width range of 0.1-10 THz. The terahertz pulse 11 is then focused by the first off-axis parabolic mirror 12 (4-inch focal length) and illuminates the sample 28 at the focal point. The terahertz pulse interacting with the sample is then collected and collimated by the second off-axis parabolic mirror 13 (4-inch focal length). Finally, it is reflected and focused by the third off-axis parabolic mirror 14 (2-inch focal length) and guided to a 100 μm thick substrate. <110> Oriented zinc telluride (ZnTe) probe crystal 22 surface.

[0057] In the optical path adjustment coupling module, the probe pulse output from the beam splitter 4 is reflected sequentially by the fourth reflector 15, the fifth reflector 16, the sixth reflector 17, the seventh reflector 18, the eighth reflector 19, and the ninth reflector 20, and then focused by the second convex lens 21. The focused probe pulse passes through the central hole of the third off-axis parabolic mirror 14 and propagates to the surface of the probe crystal 22, spatially coinciding with the focused terahertz pulse, i.e., focusing onto the same position on the crystal surface. During the reflection process, the sixth reflector 17 and the seventh reflector 18 are mounted on a linear displacement stage, which drives the optical path adjustment to ensure that the probe pulse and the terahertz wave pulse that finally illuminate the surface of the probe crystal 22 coincide in time.

[0058] The aforementioned detector crystal 22 is part of the detection optical system, which, in addition to the detector crystal 22, also includes other device units required by the standard electro-optic sampling module. Specifically, the detection pulse carrying terahertz electric field information emitted from the detector crystal 22 then passes sequentially through the third convex lens 24, the quarter-wave plate 25, and the Wollaston prism 26 before being detected by the balanced detector 27. The third convex lens 24 is used to collimate the detection pulse so that it is transmitted parallel to the quarter-wave plate 25. Finally, the terahertz time-domain signal can be obtained from the electrical signal of the balanced detector 27.

[0059] The time-domain spectroscopy system in this embodiment has three functions: terahertz emission, ultra-wideband terahertz detection, and serving as an ultra-wideband terahertz time-domain spectroscopy system.

[0060] First, the terahertz emission module. To generate ultra-wideband terahertz pulses, this time-domain spectroscopy system uses a spin terahertz emitter 10 in the form of a tungsten (1.9 nm)|cobalt-iron-boron (1.9 nm)|platinum (1.9 nm) three-layer heterojunction. Without placing the sample 28 at the focal point in the confocal off-axis parabolic mirror unit, a laser pulse with a pulse width of 35 fs, a repetition frequency of 1 kHz, and a pump energy of 5.5 mJ is input through a Ti:sapphire laser amplifier. The terahertz time-domain spectral signal and frequency-domain spectral signal acquired by this time-domain spectroscopy system are shown below. Figure 2 and Figure 3 As shown, the time-domain spectroscopy system in this embodiment can generate terahertz pulses with a continuous spectral width of 0.1-10 THz under laser pumping with a pulse width of 35 fs. Of course, the spin terahertz emitter 10 in this embodiment can also be replaced with other terahertz emitter samples to detect the emission performance of other terahertz emitters, providing a reliable characterization system for the development of terahertz sources.

[0061] Secondly, there is the ultra-wideband terahertz detection function. This time-domain spectroscopic system uses a 100 μm thick, crystal-oriented... <110> The ZnTe detector crystal 22, used for electro-optic sampling, can accurately detect terahertz spectra in the range of 0.1-10 THz. Furthermore, the ultra-wideband terahertz source of 0.1-10 THz provided by the spin terahertz emitter 10 also provides research conditions for studying the performance of novel terahertz detector crystals. In other words, in this embodiment, the ZnTe detector crystal 22 can be replaced with other detector crystals that require further investigation, allowing for precise characterization of their performance.

[0062] Finally, the ultra-wideband terahertz time-domain spectroscopy system is described. This system provides a 0.1-10 THz generation and detection module. By placing the sample 28 at the sample placement position, it can not only study the absorption of terahertz pulses by matter but also the shielding effect of matter on terahertz pulses. This system pushes the study of matter-terahertz interactions to higher frequency bands and has enormous application prospects in material characterization and terahertz shielding material research.

[0063] The embodiments described above are merely some preferred implementations of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A time-domain spectroscopic system capable of generating and detecting ultra-wideband terahertz pulses, characterized in that, Includes a laser source, a beam splitting module, an optical path adjustment coupling module, a terahertz emission module, a sample detection module, and an electro-optic sampling module; The laser source is used to output laser pulses with a pulse width of no more than 35 fs (1). The beam splitting module is used to split the laser pulse (1) into a pump pulse and a probe pulse; The terahertz emission module is used to first modulate the pump pulse through a chopper (6) and then send it into a beam expansion system to form a collimated pump beam, which is then irradiated onto a spin terahertz emitter (10) in the form of a three-layer heterojunction composed of a tungsten layer, a cobalt iron boron layer and a platinum layer, to generate an ultra-wideband terahertz pulse covering a continuous spectral range of 0.1-10 THz. The sample detection module is used to introduce the ultra-wideband terahertz pulse into the confocal off-axis parabolic mirror unit, and after interacting with the sample to be tested (28) at the focal point, it is re-collimated and output. The optical path adjustment coupling module is used to adjust the optical path of the detection pulse so that it coincides with the terahertz pulse collimated by the sample detection module in time, and to focus the detection pulse and the terahertz pulse in space and then synchronously irradiate the detection crystal (22) in the electro-optic sampling module. The electro-optic sampling module uses <110> The crystal orientation of the ultrathin ZnTe crystal is used as the detector crystal (22) to obtain the terahertz time domain signal through electro-optic detection.

2. The time-domain spectroscopic system capable of generating and detecting ultra-wideband terahertz pulses as described in claim 1, characterized in that, The center wavelength of the laser pulse (1) is 800~1550 nm, the pulse width is no more than 35 fs, and the repetition frequency is no less than 1 kHz.

3. The time-domain spectroscopic system capable of generating and detecting ultra-wideband terahertz pulses as described in claim 1, characterized in that, The beam splitting module consists of a half-wave plate (3) and a polarizing beam splitter (4) arranged sequentially along the optical path.

4. The time-domain spectroscopic system capable of generating and detecting ultra-wideband terahertz pulses as described in claim 1, characterized in that, The beam expanding system consists of a concave lens (7) and a first convex lens (8) arranged sequentially along the optical path.

5. The time-domain spectroscopic system capable of generating and detecting ultra-wideband terahertz pulses as described in claim 1, characterized in that, The spin terahertz emitter (10) is obtained by forming a three-layer heterojunction on the surface of a SiO2 substrate by magnetron sputtering, wherein the thickness of the tungsten layer, cobalt iron boron layer and platinum layer in the three-layer heterojunction is 1.8~2.0 nm.

6. The time-domain spectroscopic system for generating and detecting ultra-wideband terahertz pulses as described in claim 1, characterized in that, The confocal off-axis parabolic mirror unit is composed of a first confocal off-axis parabolic mirror (12) and a second off-axis parabolic mirror (13), and the focal position is used as the placement position of the sample to be tested (28) during testing; the ultra-wideband terahertz pulse output by the terahertz emission module is focused by the first off-axis parabolic mirror (12) and interacts with the sample to be tested (28), and is then collimated and output again by the second off-axis parabolic mirror (13).

7. The time-domain spectroscopic system capable of generating and detecting ultra-wideband terahertz pulses as described in claim 1, characterized in that, The optical path adjustment coupling module includes an optical path adjustment unit driven by a linear displacement stage, a second convex lens (21), and a third off-axis parabolic mirror (14). The detection pulse generated by the beam splitting module first passes through the optical path adjustment unit to adjust the optical path, and then is focused by the second convex lens (21) and passes through the light-transmitting hole on the third off-axis parabolic mirror (14) to irradiate a designated position on the surface of the detection crystal (22). The terahertz pulse collimated and output by the sample detection module is focused by the third off-axis parabolic mirror (14) and is irradiated together with the detection pulse to the same position on the surface of the detection crystal (22).

8. The time-domain spectroscopic system capable of generating and detecting ultra-wideband terahertz pulses as described in claim 1, characterized in that, The electro-optic sampling module consists of a detector crystal (22), a third convex lens (24), a quarter-wave plate (25), a Wollaston prism (26), and a balanced detector (27) arranged sequentially along the optical path.

9. The time-domain spectroscopic system capable of generating and detecting ultra-wideband terahertz pulses as described in claim 1, characterized in that, The thickness of the ultrathin ZnTe crystal is 100 μm.

10. The time-domain spectroscopic system for generating and detecting ultra-wideband terahertz pulses as described in claim 1, characterized in that, The time-domain spectral system is also equipped with a series of mirrors to change the optical path in order to optimize the spatial layout of the system.

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