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Article List
2024, 22(8):807-812.
DOI: 10.11805/TKYDA2024231
Abstract:
Terahertz(THz) pulses can be generated by pumping photoconductive antennas, magnetic heterostructures, electro-optic crystals, and air, etc. with femtosecond lasers, which are mainly based on non-thermal effects such as transient changes in carriers and electric polarization under femtosecond excitation. Meanwhile, the laser heating effects inevitably occur during the interactions of femtosecond lasers with matter, and the ultrafast thermoelectric effects and the ultrafast spin caloritronics effects have gained increasing attention in recent years for the ability to generate terahertz waves. In this paper, the research progresses of THz emission induced by two ultrafast thermoelectric effects including the Seebeck effect and the Nernst effect, and two ultrafast spin caloritronics effects including the spin Seebeck effect and the anomalous Nernst effect, are introduced in detail. The ultrafast thermoelectric effects and the ultrafast spin caloritronics effects have exhibited great potential in terahertz generation, which could promote the development and the applications of THz sources and related technologies.
Terahertz(THz) pulses can be generated by pumping photoconductive antennas, magnetic heterostructures, electro-optic crystals, and air, etc. with femtosecond lasers, which are mainly based on non-thermal effects such as transient changes in carriers and electric polarization under femtosecond excitation. Meanwhile, the laser heating effects inevitably occur during the interactions of femtosecond lasers with matter, and the ultrafast thermoelectric effects and the ultrafast spin caloritronics effects have gained increasing attention in recent years for the ability to generate terahertz waves. In this paper, the research progresses of THz emission induced by two ultrafast thermoelectric effects including the Seebeck effect and the Nernst effect, and two ultrafast spin caloritronics effects including the spin Seebeck effect and the anomalous Nernst effect, are introduced in detail. The ultrafast thermoelectric effects and the ultrafast spin caloritronics effects have exhibited great potential in terahertz generation, which could promote the development and the applications of THz sources and related technologies.
2024, 22(8):813-822.
DOI: 10.11805/TKYDA2024204
Abstract:
Broadband terahertz radiation sources have an urgent practical application demand in terahertz science and technology, and are the core components for constructing terahertz application systems represented by spectroscopy and imaging. Compared with commonly used commercial terahertz sources, spin-optoelectronics-based terahertz radiation sources have a series of advantages such as ultra-wide frequency spectrum, solid-state stability, and low cost. Currently, the research on the theory, materials, and device technology of spin-optoelectronics-based terahertz radiation sources is still in its infancy. This paper mainly summarizes the terahertz generation mechanism of single-layer ferromagnetic layers in recent years, and the relationship between the polarity of terahertz radiation signals and the excitation configuration. By changing the direction of the magnetic field, the direction of the incident laser, and the direction of sample incidence, the contributions of ultrafast demagnetization, Anomalous Hall Effect(AHE), and Anomalous Nernst Effect(ANE) to the terahertz radiation characteristics can be effectively distinguished, providing a reference for the research in the field of terahertz spin-optoelectronics.
Broadband terahertz radiation sources have an urgent practical application demand in terahertz science and technology, and are the core components for constructing terahertz application systems represented by spectroscopy and imaging. Compared with commonly used commercial terahertz sources, spin-optoelectronics-based terahertz radiation sources have a series of advantages such as ultra-wide frequency spectrum, solid-state stability, and low cost. Currently, the research on the theory, materials, and device technology of spin-optoelectronics-based terahertz radiation sources is still in its infancy. This paper mainly summarizes the terahertz generation mechanism of single-layer ferromagnetic layers in recent years, and the relationship between the polarity of terahertz radiation signals and the excitation configuration. By changing the direction of the magnetic field, the direction of the incident laser, and the direction of sample incidence, the contributions of ultrafast demagnetization, Anomalous Hall Effect(AHE), and Anomalous Nernst Effect(ANE) to the terahertz radiation characteristics can be effectively distinguished, providing a reference for the research in the field of terahertz spin-optoelectronics.
2024, 22(8):823-827.
DOI: 10.11805/TKYDA2024126
Abstract:
Due to the strong absorption of terahertz(THz) by water, the detection of terahertz spectroscopy for aqueous samples faces significant challenges. To address the issue of high-sensitivity detection of aqueous samples using terahertz spectroscopy, this paper proposes and experimentally verifies a high-resolution frequency-domain spectroscopy system based on terahertz Attenuated Total Reflection(ATR). The system employs an innovative optical heterodyne coherent detection technique, achieving excellent dynamic range and resolution performance. Within the range of 0.3 to 1.2 THz, the peak dynamic range exceeds 100 dB, and the frequency resolution reaches up to 100 MHz. The innovative ATR architecture effectively enhances sensitivity, and in experimental measurements of aqueous solutions with different concentrations of α-lactose, the system has realized direct and accurate quantitative detection of the aqueous samples.
Due to the strong absorption of terahertz(THz) by water, the detection of terahertz spectroscopy for aqueous samples faces significant challenges. To address the issue of high-sensitivity detection of aqueous samples using terahertz spectroscopy, this paper proposes and experimentally verifies a high-resolution frequency-domain spectroscopy system based on terahertz Attenuated Total Reflection(ATR). The system employs an innovative optical heterodyne coherent detection technique, achieving excellent dynamic range and resolution performance. Within the range of 0.3 to 1.2 THz, the peak dynamic range exceeds 100 dB, and the frequency resolution reaches up to 100 MHz. The innovative ATR architecture effectively enhances sensitivity, and in experimental measurements of aqueous solutions with different concentrations of α-lactose, the system has realized direct and accurate quantitative detection of the aqueous samples.
2024, 22(8):828-834.
DOI: 10.11805/TKYDA2023422
Abstract:
Terahertz communication with high information transmission rate and large bandwidth capacity is considered as a key technology to achieve 6G communication, which requires efficient, stable and compact terahertz sources and detectors. In order to improve the detection performance, the quasi-optical terahertz detector based on integration of Resonant Tunneling Diode(RTD) and on-chip slot antenna is studied. Aiming at the problems of increased loss and parasitic effects of the circuit at high frequencies, a design criterion that jointly considers impedance match factor and antenna radiation efficiency is proposed, and a RTD detector at a small bias voltage is designed at 0.67 THz. The detection performance is characterized by co-simulating of High Frequency Structure Simulator(HFSS) and Advanced Design System(ADS). The current sensitivity of the detector at 0.67 THz is about 2.349 A/W at the input power of -30 dBm. Compared with the design scheme of maximizing impedance match factor at microwave frequencies, the sensitivity is increased by 28.01%.
Terahertz communication with high information transmission rate and large bandwidth capacity is considered as a key technology to achieve 6G communication, which requires efficient, stable and compact terahertz sources and detectors. In order to improve the detection performance, the quasi-optical terahertz detector based on integration of Resonant Tunneling Diode(RTD) and on-chip slot antenna is studied. Aiming at the problems of increased loss and parasitic effects of the circuit at high frequencies, a design criterion that jointly considers impedance match factor and antenna radiation efficiency is proposed, and a RTD detector at a small bias voltage is designed at 0.67 THz. The detection performance is characterized by co-simulating of High Frequency Structure Simulator(HFSS) and Advanced Design System(ADS). The current sensitivity of the detector at 0.67 THz is about 2.349 A/W at the input power of -30 dBm. Compared with the design scheme of maximizing impedance match factor at microwave frequencies, the sensitivity is increased by 28.01%.
2024, 22(8):835-841.
DOI: 10.11805/TKYDA2023299
Abstract:
Gyrotron Traveling Wave Tubes(Gyrotron-TWT) have both high power and broadband characteristics, which have broad application prospects in important military fields such as millimeter wave detection and imaging radar, electronic countermeasures, etc. The gyrotron traveling wave amplifier with large orbit electron beams can operate in high-order harmonic state, greatly reducing the operating magnetic field and even achieving superconducting free operation. It can improve the flexibility and maneuverability of Gyrotron-TWT. This paper optimizes and designs a Ka band second harmonic Gyrotron-TWT with large orbit electron beams, which adopts a longitudinal slot interaction high-frequency structure with dielectric loading to effectively suppress backwave oscillation and improve the stability of device operation. The process of beam wave interaction in the Gyrotron-TWT was simulated by using three-dimensional particle simulation software. The results show that at the condition of the electron beam voltage of 70 kV, the current of 6.5 A, the magnetic field can be reduced to 0.642 T, the corresponding output power can reach 106.5 kW, the bandwidth is 2.1 GHz, and the maximum gain is 35 dB.
Gyrotron Traveling Wave Tubes(Gyrotron-TWT) have both high power and broadband characteristics, which have broad application prospects in important military fields such as millimeter wave detection and imaging radar, electronic countermeasures, etc. The gyrotron traveling wave amplifier with large orbit electron beams can operate in high-order harmonic state, greatly reducing the operating magnetic field and even achieving superconducting free operation. It can improve the flexibility and maneuverability of Gyrotron-TWT. This paper optimizes and designs a Ka band second harmonic Gyrotron-TWT with large orbit electron beams, which adopts a longitudinal slot interaction high-frequency structure with dielectric loading to effectively suppress backwave oscillation and improve the stability of device operation. The process of beam wave interaction in the Gyrotron-TWT was simulated by using three-dimensional particle simulation software. The results show that at the condition of the electron beam voltage of 70 kV, the current of 6.5 A, the magnetic field can be reduced to 0.642 T, the corresponding output power can reach 106.5 kW, the bandwidth is 2.1 GHz, and the maximum gain is 35 dB.
6 Application of equivalent dielectric model for investigating terahertz wired transmission materials
2024, 22(8):842-850.
DOI: 10.11805/TKYDA2023315
Abstract:
The terahertz frequency band, as an important alternative for the next generation of communication technologies, faces the challenge of rapid signal attenuation with increasing carrier frequency. Terahertz wired transmission technology is an effective means to address this issue, and precise control and optimization of material dielectric properties is the key to developing high-performance wired transmission materials in the terahertz frequency range. This paper modifies polymer materials and uses a terahertz time-domain spectroscopy system to test the dielectric properties of composite materials, studying the application of traditional dielectric constant equivalent models in the development of terahertz band materials. Based on the polarization characteristics and response mechanisms of terahertz band materials, a model and method for estimating the dielectric constant and loss tangent of composite materials in the terahertz frequency range is proposed, providing a scientific model guidance for the development of new terahertz wired transmission materials and their performance regulation.
The terahertz frequency band, as an important alternative for the next generation of communication technologies, faces the challenge of rapid signal attenuation with increasing carrier frequency. Terahertz wired transmission technology is an effective means to address this issue, and precise control and optimization of material dielectric properties is the key to developing high-performance wired transmission materials in the terahertz frequency range. This paper modifies polymer materials and uses a terahertz time-domain spectroscopy system to test the dielectric properties of composite materials, studying the application of traditional dielectric constant equivalent models in the development of terahertz band materials. Based on the polarization characteristics and response mechanisms of terahertz band materials, a model and method for estimating the dielectric constant and loss tangent of composite materials in the terahertz frequency range is proposed, providing a scientific model guidance for the development of new terahertz wired transmission materials and their performance regulation.
