Effect of spin on the instability of THz plasma waves in field-effect transistors under non-ideal boundary conditions

Terahertz(THz) radiation can be generated due to the instability of THz plasma waves in field-effect transistors(FETs). In this work, we discuss the instability of THz plasma waves in the channel of FETs with spin and quantum effects under non-ideal boundary conditions. We obtain a linear dispersion relation by using the hydrodynamic equation, Maxwell equation and spin equation. The influence of source capacitance, drain capacitance, spin effects, quantum effects and channel width on the instability of THz plasma waves under the non-ideal boundary conditions is investigated in great detail. The results of numerical simulation show that the THz plasma wave is unstable when the drain capacitance is smaller than the source capacitance;the oscillation frequency with asymmetric boundary conditions is smaller than that under non-ideal boundary conditions;the instability gain of THz plasma waves becomes lower under non-ideal boundary conditions. This finding provides a new idea for finding efficient THz radiation sources and opens up a new mechanism for the development of THz technology.

Study of a rectangular coupled cavity extended interaction oscillator in sub-terahertz waves

An extended interaction oscillator （EIO） generating 120 GHz wave in sub-terahertz waves is studied by using the three-dimensional electromagnetic simulation software CST and PIC codes. A rectangular reentrant coupled-cavity is proposed as the slow-wave structure of EIO. By CST, the circuit parameters including frequency-phase dispersion, interaction impedance and characteristic impedance are simulated and calculated. The operation mode of EIO is chosen very close to the point where βL = 2π with corresponding frequency 120 GHz, the beam voltage 12 kV and the dimensions of the cavity with the period 0.5mm, the height 3mm and the width 1.4mm. Simulation results of beam-wave interaction by PIC show that the exciting frequency is 120.85 GHz and output peak power 465 W with 12-period coupled-cavity with the perveance 0.17 μP. Simulation results indicate that the EIO has very wide range of the operation voltage.

Research progress in the effects of terahertz waves on biomacromolecules

With the rapid development of terahertz technologies,basic research and applications of terahertz waves in biomedicine have attracted increasing attention.The rotation and vibrational energy levels of biomacromolecules fall in the energy range of terahertz waves;thus,terahertz waves might interact with biomacromolecules.Therefore,terahertz waves have been widely applied to explore features of the terahertz spectrum of biomacromolecules.However,the effects of terahertz waves on biomacromolecules are largely unexplored.Although some progress has been reported,there are still numerous technical barriers to clarifying the relation between terahertz waves and biomacromolecules and to realizing the accurate regulation of biological macromolecules by terahertz waves.Therefore,further investigations should be conducted in the future.In this paper,we reviewed terahertz waves and their biomedical research advantages,applications of terahertz waves on biomacromolecules and the effects of terahertz waves on biomacromolecules.These findings will provide novel ideas and methods for the research and application of terahertz waves in the biomedical field.

Vegetation scattering attenuation characteristics of terahertz wave

A terahertz(THz)wave transmitted through vegetation experiences both absorption and scattering caused by the air molecules and leaves.This paper presents the scattering attenuation characteristics of vegetation in a THz range.The theoretical path loss model near the vegetation yields the average attenuation of THz waves in a mixed channel composed of air and vegetation leaves.Furthermore,a simplified model of the vegetation structure is obtained for generic vegetation types based on a variety of parameters,such as leaf size,distribution,and moisture content.Finally,based on specific vegetation species and different levels of air humidity,the attenuation characteristics under different conditions are calculated,and the influence of different model parameters on the attenuation characteristics is obtained.

Scattering of Circularly Polarized Terahertz Waves on a Graphene Nanoantenna

We present a surface current method to model the graphene rectangular nanoantenna scattering in the terahertz band with Comsol. Compared with the equivalent thin slab method, the results obtained by the surface current method are more accurate and efficient. Then the electromagnetic scattering of circularly polarized terahertz waves on graphene nanoantennas is numerically analyzed by utilizing the surface current method. The depen- dences of the antenna resonant frequency with the circularly polarized wave on width and length are consistent with those for the linear polarized waves. These results are proved to be useful to design et^cient nanoantennas in terahertz wireless communications.

High-power terahertz radiation from surface-emitted THz-wave parametric oscillator

We report a pulsed surface-emitted THz-wave parametric oscillator based on two MgO：LiNbO3 crystals pumped by a multi-longitudinal mode Q-switched Nd：YAG laser. Through varying the phase matching angle, the tunable THzwave output from 0.79 THz to 2.84 THz is realized. The maximum THz-wave output was 193.2 n J/pulse at 1.84 THz as the pump power density was 212.5 MW/cm2, corresponding to the energy conversion efficiency of 2.42Х10-6 and the photon conversion efficiency of about 0.037%. When the pump power density changed from 123 MW/cm^2 to 148 MW/cm^2 and 164 MW/cm^2, the maximum output of the THz-wave moved to the high frequency band. We give a reasonable explanation for this phenomenon.

Simultaneous all-solid-state multi-wavelength lasers——a promising pump source for generating highly coherent terahertz waves

A diode-end-pumped Nd：YAG dual-wavelength laser operating at 1319 and 1338 nm is demonstrated. The maximum average output power of the quasi-continuous wave linearly polarized dual-wavelength laser is obtained to be 2.1 W at a repetition rate of 50 kHz with an output power instability of less than 0.38% and beam quality factor M^2 of 1.45. Using the two lines, the highly coherent and narrow linewidth terahertz radiation of 3.23 THz can be generated in an organic 4-N, N-dimethylamino-methyl-stilbazolium tosylate （DAST） crystal. Meanwhile, the multi-wavelength red laser at 659.5, 664 and 669 nm is generated by frequency doubling and sum frequency processes in a lithium triborate （LBO） crystal. The average red laser output power is enhanced up to 1.625 W at a repetition rate of 15 kHz with an output power instability of better than 0.53% and beam quality factor M^2 of 6.05. Using the three lines, it is possible to generate the multi-wavelength THz radiation of 3.3, 3.43 and 6.73 THz in an appropriate difference frequency crystal.

Nonlinear Terahertz Electromagnetic Waves in SrTiO3 Crystals under Focusing

The nonlinear waves of terahertz (THz) range are investigated in the paraelectric crystals SrTiO3 at the temperatures ~77 K. The frequency dispersion is important there. In the absence of a bias electric field the dominating nonlinearity is cubic. The frequency dispersion and nonlinearity correspond to existence of envelope solitons and the modulation instability (MI) of long input pulses, whereas in the transverse direction MI is absent. There exists a possibility to generate the regular sequences of short THz pulses due to MI in bounded SrTiO3 crystals. The focusing of input long pulses reduces the threshold of MI, increases the output amplitudes of the short pulses, and provides more stable generation of the short pulses. It is investigated the frequency multiplication of THz electromagnetic radiation in bounded paraelectric SrTiO3 when a bias electric field is applied. The dominating nonlinearity is quadratic there. The frequency dispersion and the transverse width of the input wave beams affect the generation of higher harmonics. It is possible to select the certain numbers of higher harmonics by means of the optimum length of the crystal, by the width of the beam of the input first harmonic, and by the focusing of the input first harmonic.

6G无线通信THz电子学、光子学、等离子体波器件及应用的新进展(续)

移动通信技术已成为现代智能信息网络发展的带动的重要技术之一。继sub-6 GHz和毫米波频段的5G移动通信成为当今移动通信的发展主流之后,预计以亚THz/THz频段的6G移动通信将于2030年到来。综述了用于未来6G无线通信的THz电子学、光子学、等离子体波器件及应用的新进展。综述并分析了当今THz器件与电路以及典型应用的关键技术的发展现状与趋势,包含真空电子领域的行波管、碰撞雪崩渡越时间(IMPATT)二极管、THz谐振隧穿二极管(RTD)、THz肖特基势垒二极管(SBD)、THz CMOS、THz SiGe BiCMOS、THz InP HEMT/InP HBT、D波段GaN HEMT、光子学辅助的太赫兹波技术、石墨烯为代表的二维材料器件与电路。THz器件的应用创新重点包含四个方面:通道测量与建模、多输入多输出(MIMO)天线阵列、智能可重构反射阵列以及通信局域网络架构和实验平台。

6G无线通信THz电子学、光子学、等离子体波器件及应用的新进展

移动通信技术已成为由现代智能信息网络发展带动的重要技术之一。继sub-6 GHz和毫米波频段的5G移动通信成为当今移动通信的发展主流之后,预计以亚THz/THz频段的6G移动通信将于2030年到来。综述了用于未来6G无线通信的THz电子学、光子学、等离子体波器件及应用的新进展。综述并分析了当今THz器件与电路以及典型应用的关键技术的发展现状与趋势,包含真空电子领域的行波管、碰撞雪崩渡越时间(IMPATT)二极管、THz谐振隧穿二极管(RTD)、THz肖特基势垒二极管(SBD)、THz CMOS、THz SiGe BiCMOS、THz InP HEMT/InP HBT、D波段GaN HEMT、光子学辅助的太赫兹波技术、石墨烯为代表的二维材料器件与电路。THz器件的应用创新重点包含四个方面:通道测量与建模、多输入多输出(MIMO)天线阵列、智能可重构反射阵列以及通信局域网络架构和实验平台。

Anomalous behaviours of terahertz reflected waves transmitted from GaAs induced by optical pumping

Femtosecond pump-terahertz probe studies of carrier dynamics in semi-insulating CaAs have been investigated in detail for various pump powers. It is observed that, at high pump powers, the reflection peaks flip to the opposite polarity and dramatically enhance as the pump arrival time approaches the reflected wave of the terahertz pulse. The abnormal polarity-flip and enhancement can be interpreted by the pump-induced enhancement in the photoconductivity of GaAs and half-wave loss. Moreover, the carrier relaxation processes and surface states filling in GaAs are also studied in these measurements.

Terahertz Plasma Waves in Two Dimensional Quantum Electron Gas with Electron Scattering

We investigate the Terahertz （THz） plasma waves in a two-dimensional （2D） electron gas in a nanometer field effect transistor （FET） with quantum effects, the electron scattering, the thermal motion of electrons and electron exchange-correlation. We find that, while the elec- tron scattering, the wave number along y direction and the electron exchange-correlation suppress the radiation power, but the thermal motion of electrons and the quantum effects can amplify the radiation power. The radiation frequency decreases with electron exchange-correlation con- tributions, but increases with quantum effects, motion of electrons. It is worth mentioning that radiation frequency. These properties could be plasma oscillations in nanometer FET. the wave number along y direction and thermal the electron scattering has scarce influence on the of great help to the realization of practical THz

Terahertz Transmission Imaging with 2.52 THz Continuous Wave

In this article, two terahertz transmission imaging systems are built with a 2.52 THz continuous wave laser and two types of sensors. One is array scanning system using a 124×124 pyro-electric array camera as the detector; the other is a point-wise scanning system utilizing a Golay cell as the detector. The imaging speed and quality is briefly analyzed. Terahertz （THz） imaging results demonstrate that the array scanning system has higher imaging speed with lower resolution. The point-wise scanning system has higher imaging quality with lower speed.

The instability of terahertz plasma waves in cylindrical FET

In this paper,the Dyakonov-Shur instability of terahertz(THz)plasma waves has been analyzed in gated cylindrical field effect transistor(FET).In the cylindrical FET,the hydrodynamic equations in cylindrical coordinates are used to describe the THz plasma wave in twodimensional electronic gas.The research results show that the oscillation frequency of the THz plasma wave is increased by increasing the component of wave in the circumferential direction,but in stability increment of the THz plasma wave are in creased by increasing the radius of channel.

Propagation of terahertz waves in nonuniform plasma slab under “electromagnetic window”

The application of magnetic fields, electric fields, and the increase of the electromagnetic wave frequency are upand-coming solutions for the blackout problem. Therefore, this study considers the influence of the external magnetic field on the electron flow and the effect of the external electric field on the electron density distribution, and uses the scattering matrix method(SMM) to perform theoretical calculations and analyze the transmission behavior of terahertz waves under different electron densities, magnetic field distributions, and collision frequencies. The results show that the external magnetic field can improve the transmission of terahertz waves at the low-frequency end. Magnetizing the plasma from the direction perpendicular to the incident path can optimize the right-hand polarized wave transmission. The external electric field can increase the transmittance to some extent, and the increase of the collision frequency can suppress the right-hand polarized wave cyclotron resonance caused by the external magnetic field. By adjusting these parameters, it is expected to alleviate the blackout phenomenon to a certain extent.

Creation of multi-frequency terahertz waves by optimized cascaded difference frequency generation

A new scheme which generates multi-frequency terahertz(THz)waves from planar waveguide by the optimized cascaded difference frequency generation(OCDFG)is proposed.A THz wave with frequencyω_(T1)is generated by the OCDFG with two infrared pump waves,and simultaneously a series of cascaded optical waves with a frequency intervalω_(T1)is generated.The THz wave with a frequency of M-timesω_(T1)is generated by mixing the m-th-order and the(m+M)-th-order cascaded optical wave.The phase mismatch distributions of cascaded difference frequency generation(CDFG)are modulated by changing the thickness of planar waveguide step by step,thereby satisfying the phase-matching condition from first-order to high-order cascaded Stokes process step by step.As a result,the intensity of THz wave can be enhanced and modulated by controlling the cascading order of OCDFG.

THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves

We propose a novel scheme for THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves(HSWs).The repeated frequency conversions are accomplished by oscillations of Stoke waves in resonant cavity(RC)where low-order Stokes waves(LSWs)are converted to high-order Stokes waves again and again.The continuous frequency conversions are accomplished by optimized cascaded difference frequency generation(OCDFG)where the poling periods of the optical crystal are aperiodic leading to the frequency conversions from low-order Stokes waves to high-order Stokes waves uninterruptedly and unidirectionally.Combined with the repeated and continuous frequency conversions,the optical-to-THz energy conversion efficiency(OTECE)exceeds 26%at 300 K and 43%at 100 K with pump intensities of 300 MW/cm^(2).

Results and Prospects of Experimental Validation of the Use of Electromagnetic Waves at Terahertz Frequencies of Cellular Metabolites in Clinical Practice

The paper presents the results of experimental studies of the effect of irradiation with electromagnetic waves terahertz frequencies of molecular spectrum of emission and absorption of nitric oxide and atmospheric oxygen on animals in a state of acute and chronic immobilization stress, a condition regarded as a model of violations in different parts of the vascular system including microcirculation specific for different parts of the vascular system, including the microcirculation characteristic of various diseases of the cardiovascular system.

Correction of Disorders in Tissue Perfusion, Blood Coagulation and Fibrinolysis with Orbita Apparatus on Terahertz Waves of Cell Metabolites

This article contains information on principle of operation, technical parameters and possible application of Orbita apparatus for hemodynamic, fibrinolytic and peripheral perfusion disorders treatment. A single exposure to terahertz waves emitted by Orbita apparatus, corresponding to frequencies of molecular absorption and emission spectra of atmospheric oxygen (129.0 GHz), completely cures coagulant and fibrinolytic disorders of animals with acute immobilization stress. A course of treatment with electromagnetic waves corresponding to frequencies of molecular absorption and emission spectra of nitrogen oxide (150.176 - 150.664) leads to normalization of disrupted peripheral tissue perfusion parameters of animal undergoing treatment and stimulates basal and induced output of nitrogen oxide. This leads to decrease in peripheral vascular resistance to microcirculation and increase in blood flow to microvasculature. Experimental data provided in this article serves as a proof of viability of Orbita apparatus for treatment of coagulant, fibrinolytic and tissue perfusion disorders.

The Instability of Terahertz Plasma Waves in Two Dimensional Gated and Ungated Quantum Electron Gas

The instability of terahertz（THz）plasma waves in two-dimensional（2D）quantum electron gas in a nanometer field effect transistor（FET）with asymmetrical boundary conditions has been investigated.We analyze THz plasma waves of two parts of the 2D quantum electron gas：gated and ungated regions.The results show that the radiation frequency and the increment（radiation power）in 2D ungated quantum electron gas are much higher than that in 2D gated quantum electron gas.The quantum effects always enhance the radiation power and enlarge the region of instability in both cases.This allows us to conclude that 2D quantum electron gas in the transistor channel is important for the emission and detection process and both gated and ungated parts take part in that process.