A high-field-intensity and ultra-wide-spectrum terahertz transmitter system

Abstract

The invention discloses a high field strength ultra-wide spectrum terahertz emitter system, comprising a pump laser, a concave lens and a first off-axis parabolic mirror, indium tin oxide, W / Co 20 Fe 60 B 20 The device consists of a three-layer heterostructure of 100 nm / Pt, a second off-axis parabolic mirror, and a detection crystal. When the pump laser impinges on the three-layer heterostructure, it emits terahertz radiation in both forward and backward directions. The forward terahertz radiation is reflected by a reflector, while the backward terahertz radiation is reflected by indium tin oxide. Both are then focused by the second off-axis parabolic mirror onto the detection crystal for detection, enhancing the forward terahertz radiation. The combined forward and backward signals are 2.5 times stronger than the forward signal.

Description

Technical Field

[0001] The present invention relates to the technical field of terahertz sources, specifically to a high-field-intensity and ultra-wide-spectrum terahertz emitter system, and more specifically to a high-field-intensity and ultra-wide-spectrum terahertz emitter system based on ultrafast spin current injection and inverse spin Hall effect in a ferromagnetic / non-magnetic heterojunction. Background Art

[0002] High-field, ultra-broadband terahertz (THz) sources have widespread and crucial applications in a wide range of fields, including condensed matter physics, medical imaging systems, high-speed wireless communications, security inspections, and radar imaging. As the foundation of THz technology research and development, THz sources have long garnered significant attention. For many years, THz generation has primarily involved methods such as optical rectification-based THz sources, laser-induced plasma-based THz sources, and solid-state photocurrent THz emitters. Of these methods, optical rectification-based THz sources can achieve high field intensities but have a narrow spectrum. Laser-induced plasma-based THz sources can achieve both high field intensities and a wide spectrum, but this approach is understudied, suffers from large errors, and is difficult to maintain. Furthermore, solid-state photocurrent-based THz emitters cannot simultaneously meet the requirements for both a wide spectrum and high field intensities.

[0003] A recent breakthrough in this area is the spintronic THz emitter (STE), discovered by a German research team. This source can achieve broadband THz emission up to 30 THz. The team can generate THz fields up to 300 kV / cm, and the emission spectrum of this large-area spin THz source is wide and bandwidth-free, without phase matching issues. This represents a breakthrough in conventional THz emission mechanisms, thus avoiding the issues of phonon absorption and phase mismatch that traditional THz sources face. However, this THz source currently utilizes only forward-emitting THz, making it significantly weaker than traditional THz sources. While the spectrum is relatively broad, it cannot be considered high-field. Summary of the Invention

[0004] Purpose of the invention: In view of the problems and shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a high-field-intensity and ultra-wide-spectrum terahertz emitter system, which solves the problem of insufficient field strength of the existing electron spin-based terahertz source and the problem of insufficient spectrum of the traditional high-field-intensity terahertz source.

[0005] Technical solution: To achieve the above-mentioned invention purpose, the technical solution provided by the present invention is a high-field intensity and ultra-wide spectrum terahertz emitter system, comprising a pump laser, a concave lens and a first off-axis parabolic mirror, an indium tin oxide film, a three-layer heterostructure, a second off-axis parabolic mirror, a first terahertz reflector, a second terahertz reflector, a third terahertz reflector, a fourth terahertz reflector, a fifth terahertz reflector and a detection crystal. The pump laser is first expanded by a concave lens and a first off-axis parabolic mirror, and then irradiated to the three-layer heterostructure. The terahertz generated by the three-layer heterostructure is simultaneously emitted in the forward and backward directions. The terahertz emitted backward is reflected by the indium tin oxide film, and then reflected by the first terahertz reflector and the second terahertz reflector to the second off-axis parabolic mirror in sequence. The terahertz emitted forward is reflected by the third terahertz reflector, the fourth terahertz reflector and the fifth terahertz reflector to the second off-axis parabolic mirror in sequence. The second off-axis parabolic mirror focuses the forward and backward terahertz onto the detection crystal for detection.

[0006] Furthermore, the three-layer heterostructure is grown in the order of antiferromagnetic material-ferromagnetic material-antiferromagnetic material, the three-layer heterostructure is grown on a silicon dioxide substrate, and the three-layer heterostructure is placed in a magnetic field.

[0007] Furthermore, the angle between the indium tin oxide film and the backward emitted terahertz in the optical path is 45°, the surface resistance of the indium tin oxide film is not greater than 15Ω / sq, and the indium tin oxide film is grown on silicon dioxide.

[0008] Furthermore, a stepper motor is included, and the fourth terahertz reflector and the fifth terahertz reflector are both placed on the stepper motor. The optical path is adjusted by moving the position of the stepper motor so that the optical path of the terahertz emitted forward is the same as that of the terahertz emitted backward.

[0009] Beneficial Effects: The system of the present invention enhances the forward terahertz field strength generated by electron spin-based terahertz sources by 2.5 times. Theoretically, the terahertz field strength generated by this system can reach 750 kV / cm, and the spectral width can reach 30 THz. This invention enhances the terahertz field strength generated by existing electron spin-based terahertz emitters. The invention collects the backward-emitted terahertz and successfully combines it with the forward-emitted terahertz, achieving signal enhancement. This is of great significance for the research of electron spin-based terahertz sources. Furthermore, the invention is low-cost and has a significant impact on the application of terahertz. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Schematic diagram of the optical path of the high-field-intensity and ultra-wide-spectrum terahertz transmitter system;

[0011] Figure 2 This is the time domain diagram of the terahertz signal actually generated by the high-field intensity and ultra-wide spectrum terahertz transmitter system. DETAILED DESCRIPTION

[0012] The present invention is further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of use of the present invention. After reading the present invention, modifications of various equivalent forms of the present invention made by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0013] We found that the heterostructure emits terahertz forward and backward at the same time. Therefore, the present invention collects the backward-emitted terahertz by adding an indium tin oxide film in the optical path, synthesizing the two terahertz signals together, thereby enhancing the original terahertz signal while maintaining a wide spectrum, and thus realizing a terahertz emitter system with a wide spectrum and high field strength.

[0014] The present invention includes a pump laser 1, a concave lens 2 and a first off-axis parabolic mirror 3, an indium tin oxide film 4, a three-layer heterostructure 5, a second off-axis parabolic mirror 6, a first terahertz reflector 7, a second terahertz reflector 12, a third terahertz reflector 13, a fourth terahertz reflector 14, a fifth terahertz reflector 15, a stepper motor 11, a rubidium magnet 16, and a detection crystal 8. The pump laser 1 is first expanded by the concave lens 2 and the first off-axis parabolic mirror 3 before being irradiated onto the three-layer heterostructure 5 for terahertz pumping. The three-layer heterostructure 5 is positioned between two rubidium magnets 16. The terahertz generated by the three-layer heterostructure 5 is emitted simultaneously in both the forward and backward directions. The backward-emitted terahertz 9 is reflected by the indium tin oxide film 4 and then sequentially reflected by the first terahertz reflector 7 and the second terahertz reflector 12 onto the second off-axis parabolic mirror 6. The forward-emitted terahertz is sequentially reflected by the third terahertz reflector 13, the fourth terahertz reflector 14, and the fifth terahertz reflector 15 onto the second off-axis parabolic mirror 6. The second off-axis parabolic mirror 6 focuses the forward-emitted terahertz 10 and the backward-emitted terahertz 9 onto the detection crystal 8 for detection.

[0015] The present invention will be further described below with reference to the accompanying drawings.

[0016] like Figure 1As shown, an 800nm ​​pump laser 1 is beam-expanded through a concave lens 2 and a first off-axis parabolic mirror 3 to achieve a larger pumping area. An indium tin oxide film 4 is placed at a 45-degree angle in the pump laser's optical path. Most of the laser light passes through the indium tin oxide and strikes a three-layer heterostructure 5, which is positioned between two rubidium magnets 16. This structure radiates forward-emitting terahertz radiation 9 and backward-emitting terahertz radiation 10. The backward-emitting terahertz radiation 9 follows a spatially colinear path with the pump laser 1, but in opposite directions. The backward-emitting terahertz radiation 9 is reflected by the indium tin oxide film 4, then sequentially by the first terahertz reflector 7 and the second terahertz reflector 12 before being incident on the second off-axis parabolic mirror 6. The forward-emitting terahertz radiation 10 is reflected by the fourth terahertz reflector 14 and the fifth terahertz reflector 15, both mounted on the stepper motor 11, before also being incident on the second off-axis parabolic mirror 6. The backward-emitted terahertz 9 and the forward-emitted terahertz 10 are incident on the second off-axis parabolic mirror 6 in parallel, are focused by the second off-axis parabolic mirror 6, and are incident on the detection crystal 8 together. By adjusting the position of the stepping motor 11, the optical path of the forward-emitted terahertz 10 and the backward-emitted terahertz 9 are made the same. By adjusting the second terahertz reflector 12 and the fifth terahertz reflector 15, the light spot of the forward-emitted terahertz 10 and the light spot of the backward-emitted terahertz 9 can be overlapped, ultimately achieving the effect of synthesizing the two signals and enhancing the forward-emitted terahertz 10.

[0017] Parameters of key components in the system: Pump laser 1 has a repetition frequency of 1000 Hz, a pulse width of 100 fs, a central wavelength of 800 nm, and a pump power of 400 mW; the surface resistance of the indium tin oxide film 4 is 7 Ω / sq; the specific structure and thickness parameters of the three-layer heterostructure 5 are in the following order: W (thickness is 1.8 nm), Co 20 Fe 60 B 20 (thickness is 2nm), Pt (thickness is 1.8nm); the second off-axis parabolic mirror 6 has a diameter of 4 inches and a focal length of 3 inches; the detection crystal 8 is a ZnTe crystal.

[0018] according to Figure 1 As shown in the figure, a high field strength ultra-wide spectrum terahertz transmitter system is built and detected, and the Figure 2 The waveform of the terahertz signal is shown in Figure 1. For the convenience of display, the signal is time-shifted in the figure. 前向 is the waveform of the forward-transmitted terahertz 10, with an amplitude of 1.3 (unitless), E 后向 The terahertz 9 emitted backward has an amplitude of 2.0, and the ratio of the terahertz 10 emitted forward to the terahertz 9 emitted backward is 1.:1.5. 合成When two terahertz waves arrive at the same time, the amplitude is 3.3, that is, the bidirectional signal is 2.5 times that of the previous unidirectional signal, which means that the present invention has achieved a 2.5-fold enhancement of the emission field strength of the original spin terahertz source. If the same conditions as the previous research on achieving 300kV / cm are used, the field strength of 750kV / cm can be achieved in theory, and the bandwidth can reach 30THz.

Claims

1. A high-field-intensity and ultra-wide-spectrum terahertz transmitter system, characterized in that: The invention comprises a pump laser, a concave lens and a first off-axis parabolic mirror, an indium tin oxide film, a three-layer heterostructure, a second off-axis parabolic mirror, a first terahertz reflector, a second terahertz reflector, a third terahertz reflector, a fourth terahertz reflector, a fifth terahertz reflector and a detection crystal. The pump laser is first expanded by the concave lens and the first off-axis parabolic mirror, and then irradiated to the three-layer heterostructure for terahertz pumping. The terahertz generated by the three-layer heterostructure is emitted in two directions, forward and backward, and the terahertz emitted backward is reflected by the indium tin oxide film and then reflected by the first terahertz reflector in turn. The terahertz reflector and the second terahertz reflector are reflected onto the second off-axis parabolic mirror, and the forward-emitted terahertz is sequentially reflected onto the second off-axis parabolic mirror by the third terahertz reflector, the fourth terahertz reflector and the fifth terahertz reflector. The second off-axis parabolic mirror focuses the forward and backward terahertz onto the detection crystal for detection. The system also includes a stepper motor, and the fourth terahertz reflector and the fifth terahertz reflector are both placed on the stepper motor. The optical path is adjusted by moving the position of the stepper motor so that the optical path of the forward-emitted terahertz is the same as that of the backward-emitted terahertz.

2. The high-field-intensity and ultra-wide-spectrum terahertz transmitter system according to claim 1, characterized in that: The three-layer heterostructure is grown in the order of antiferromagnetic material-ferromagnetic material-antiferromagnetic material, the three-layer heterostructure is grown on a silicon dioxide substrate, and the three-layer heterostructure is placed in a magnetic field.

3. The high-field-intensity and ultra-wide-spectrum terahertz transmitter system according to claim 1, characterized in that: The included angle between the indium tin oxide film and the backward emitted terahertz in the optical path is 45°, the surface resistance of the indium tin oxide film is 7Ω / sq, and the indium tin oxide film is grown on silicon dioxide.

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