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 biomacromolecule...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.展开更多
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 curren...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.展开更多
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 ...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.展开更多
We theoretically investigate the characteristics of terahertz(THz) radiation from monolayer graphene exposed to normal incident few-cycle laser pulses, by numerically solving the extended semiconductor Bloch equations...We theoretically investigate the characteristics of terahertz(THz) radiation from monolayer graphene exposed to normal incident few-cycle laser pulses, by numerically solving the extended semiconductor Bloch equations. Our simulations show that the THz spectra in low frequency regions are highly dependent on the carrier envelope phase(CEP) of driving laser pulses. Using an optimal CEP of few-cycle laser pulses, we can obtain broadband strong THz waves, due to the symmetry breaking of the laser-graphene system. Our results also show that the strength of the THz spectra depend on both the intensity and central wavelength of the laser pulses. The intensity dependence of the THz wave can be described by the excitation rate of graphene, while wavelength dependence can be traced back to the band velocity and the population of graphene. We find that a near single-cycle THz pulse can be obtained from graphene driven by a mid-infrared laser pulse.展开更多
We propose a novel metasurface based on a combined pattern of outer C-shaped ring and inner rectangular ring.By Fourier convolution operation to generating different predesigned sequences of metasurfaces,we realize va...We propose a novel metasurface based on a combined pattern of outer C-shaped ring and inner rectangular ring.By Fourier convolution operation to generating different predesigned sequences of metasurfaces,we realize various functionalities to flexible manipulate terahertz waves including vortex terahertz beam splitting,anomalous vortex terahertz wave deflection,vortex terahertz wave splitting and deflection simultaneously.The incident terahertz wave can be flexibly controlled in a single metasurface.The designed metasurface has an extensive application prospect in the field of future terahertz communication and sensing.展开更多
We theoretically and numerically demonstrate that a transmission-type electrically tunable polarizer can be realized by using graphene ribbons supported on a dielectric film with a graphene sheet behind. The polarizat...We theoretically and numerically demonstrate that a transmission-type electrically tunable polarizer can be realized by using graphene ribbons supported on a dielectric film with a graphene sheet behind. The polarization mechanism originates from the antenna plasmon resonance of graphene stripes. The results of full-wave numerical simulations reveal that transmittance of 0.70 for one polarization and 0.0073 for another polarization can be obtained at normal incidence. The transmission-type electrically tunable polarizer provides and facilitates a variety of applications, including filtering, detecting, and imaging.展开更多
In recent years, there has been increased interest in the terahertz waveband for application to ultra-high-speed wireless communications and remote sensing systems. However, atmospheric propagation at these wavelength...In recent years, there has been increased interest in the terahertz waveband for application to ultra-high-speed wireless communications and remote sensing systems. However, atmospheric propagation at these wavelengths has a significant effect on the operational stability of systems using the terahertz waveband, so elucidating the effects of rain on propagation is a topic of high interest. We demonstrate various methods for calculating attenuation due to rain and evaluate these methods through comparison with calculated and experimental values. We find that in the 90 - 225 GHz microwave band, values calculated according to Mie scattering theory using the Best and P-S sleet raindrop size distributions best agree with experimental values. At 313 and 355 GHz terahertz-waveband frequencies, values calculated according to Mie scattering theory using the Weibull distribution and a prediction model following ITU-R recommendations best agree with experimental values. We furthermore find that attenuation due to rain increases in proportion to frequency for microwave-band frequencies below approximately 50 GHz, but that there is a peak at around 100 GHz, above which the degree of attenuation remains steady or decreases. Rain-induced attenuation increases in proportion to the rainfall intensity.展开更多
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 ext...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.展开更多
Based on coupled quantum dots, we present an interesting optical effect in a four-level loop coupled system. Both the two upper levels and the two lower levels are designed to be almost degenerate, which induces a con...Based on coupled quantum dots, we present an interesting optical effect in a four-level loop coupled system. Both the two upper levels and the two lower levels are designed to be almost degenerate, which induces a considerable dipole moment. The terahertz wave is obtained from the low-frequency component of the photon emission spectrum. The frequency of the terahertz wave can be controlled by tuning the energy levels via designing the nanostructure appropriately or tuning the driving laser field. A terahertz wave with adjustable frequency and considerable intensity (100 times higher than that of the Rayleigh line) can be obtained. It provides an effective scheme for a terahertz source.展开更多
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 OC...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.展开更多
A novel scheme for high-efficiency terahertz(THz)wave generation based on optimized cascaded difference frequency generation(OCDFG)with planar waveguide is presented.The phase mismatches of each-order cascaded differe...A novel scheme for high-efficiency terahertz(THz)wave generation based on optimized cascaded difference frequency generation(OCDFG)with planar waveguide is presented.The phase mismatches of each-order cascaded difference frequency generation(CDFG)are modulated by changing the thickness of the waveguide,resulting in a decrement of phase mismatches in cascaded Stokes processes and an increment of phase mismatches in cascaded anti-Stokes processes simultaneously.The modulated phase mismatches enhance the cascaded Stokes processes and suppress the cascaded anti-Stokes processes simultaneously,yielding energy conversion efficiencies over 25%from optical wave to THz wave at 100 K.展开更多
High-efficiency terahertz(THz) wave generation with multiple frequencies by optimized cascaded difference frequency generation(OCDFG) is investigated at 100 K using a nonlinear crystal consisting of a periodically pol...High-efficiency terahertz(THz) wave generation with multiple frequencies by optimized cascaded difference frequency generation(OCDFG) is investigated at 100 K using a nonlinear crystal consisting of a periodically poled lithium niobate(PPLN) part and an aperiodically poled lithium niobate(APPLN) part.Two infrared pump waves with a frequency difference ω_(T1) generate THz waves and a series of cascaded optical waves in the PPLN part by cascaded difference frequency generation(CDFG).The generated cascaded optical waves with frequency interval ω_(T1) then further interact in the APPLN part by OCDFG,yielding the following two advantages.First,OCDFG in the APPLN part is efficiently stimulated by inputting multi-order cascaded optical waves rather than the only two intense infrared pump waves,yielding unprecedented energy conversion efficiencies in excess of 37% at 1 THz at 100 K.Second,THz waves with M timesω_(T1) are generated by mixing the mth-order and the(m+M)th-order cascaded optical waves by designing poling period distributions of the APPLN part.展开更多
The propagation characteristics of oblique incidence terahertz(THz) waves through non-uniform plasma are investigated by the shift-operator finite-difference time-domain(SO-FDTD) method combined with the phase matchin...The propagation characteristics of oblique incidence terahertz(THz) waves through non-uniform plasma are investigated by the shift-operator finite-difference time-domain(SO-FDTD) method combined with the phase matching condition.The electron density distribution of the non-uniform plasma is assumed to be in a Gaussian profile. Validation of the present method is performed by comparing the results with those obtained by an analytical method for a homogeneous plasma slab.Then the effects of parameters of THz wave and plasma layer on the propagation properties are analyzed. It is found that the transmission coefficients greatly depend on the incident angle as well as on the thickness of the plasma, while the polarization of the incident wave has little influence on the propagation process in the range of frequency considered in this paper. The results confirm that the THz wave can pass through the plasma sheath effectively under certain conditions,which makes it a potential candidate to overcome the ionization blackout problem.展开更多
Rain attenuation at 355.2 GHz in the terahertz wave range was measured with our new 355.2 GHz measuring system under rainfall intensities up to 25 mm/hr. Rain attenuation coefficients were also calculated using four r...Rain attenuation at 355.2 GHz in the terahertz wave range was measured with our new 355.2 GHz measuring system under rainfall intensities up to 25 mm/hr. Rain attenuation coefficients were also calculated using four raindrop-size distributions, e Marshall-Palmer (M-P), Best, Polyakova-Shifrin (P-S) and Weibull distributions, and using a specific rain attenuation model for prediction methods recommended by ITU-R. Measurements of a terahertz wave taken at 355.2 GHz were compared with our calculations. Results showed that the propagation experiment was in very good agreement with a calculation from a specific attenuation model for use in prediction method recommended by ITU-R.展开更多
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 couple...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.展开更多
Manipulation of terahertz wave by metasurfaces has shown tremendous potential in developing compact and functional terahertz optical devices.Here,we propose complementary bilayer metasurfaces for enhanced terahertz wa...Manipulation of terahertz wave by metasurfaces has shown tremendous potential in developing compact and functional terahertz optical devices.Here,we propose complementary bilayer metasurfaces for enhanced terahertz wave amplitude and phase manipulation.The metasurfaces are composed of one layer of metal cut-wire arrays and one layer of their complementary aperture arrays separated by a dielectric spacer.Through the near-field coupling between transverse magnetic resonances in the metal apertures and electric resonances in the metal cut-wires,the structures can manipulate the cross polarization conversion and phase dispersion of terahertz wave.Particularly,the designed metasurfaces demonstrate a phase delay of 180°between two orthogonal axes with the same transmission amplitude between 0.70 and 1.0 THz,enabling a 45°broadband polarization conversion.When the metal cut-wires are rotated with respect to the apertures or the thickness of the dielectric spacer is changed,the amplitude and phase dispersion of the transmitted terahertz wave can be tuned.Such complementary coupled bilayer metasurfaces offer a new method to control the amplitude and phase dispersion of terahertz wave and promise great potential for applications in terahertz meta-devices.展开更多
Terahertz (THz)-wave generation has been conducted based on difference frequency mixing (DFM) process with phonon-polariton excitation of ε-GaSe single crystals implemented with liquid-phase solution growth using the...Terahertz (THz)-wave generation has been conducted based on difference frequency mixing (DFM) process with phonon-polariton excitation of ε-GaSe single crystals implemented with liquid-phase solution growth using the temperature difference method under controlled vapour pressure for the first time. The type-eoo phase matching condition for the DFM process at around 10 THz is satisfied by changing the incident angle into the crystal. The maximum conversion efficiency in the present DFG process is about 10-6?J-1?using a 0.1-mm-thick GaSe single crystal with the only ε- phase polytype, which can be greater than that of the commercially available Bridgman grown GaSe crystal including both ε- and γ-phase polytypes.展开更多
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 expos...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.展开更多
In this Letter,we employ fused silica and two types of optical glass as examples to investigate the coherent terahertz(THz)wave emission from laser-ionized isotropic transparent dielectrics.Based on the laser energy a...In this Letter,we employ fused silica and two types of optical glass as examples to investigate the coherent terahertz(THz)wave emission from laser-ionized isotropic transparent dielectrics.Based on the laser energy and incident angle dependences,we ascribe the THz emission to the ponderomotive force-induced dipole oscillation.Additionally,our investigation on the dependence of THz amplitude on the laser pulse duration confirms the dominant role of avalanche ionization in solid dielectrics.The THz emission can be utilized to indirectly monitor the ultrafast dynamics of carrier generation and motion during the laser ionization process of solid dielectrics.展开更多
Ultra-broadband,intense,coherent terahertz(THz)radiation can be generated,detected,and manipulated using laser-induced gas or liquid plasma as both the THz wave transmitter and detector,with a frequency coverage spann...Ultra-broadband,intense,coherent terahertz(THz)radiation can be generated,detected,and manipulated using laser-induced gas or liquid plasma as both the THz wave transmitter and detector,with a frequency coverage spanning across and beyond the whole THz gap."Such a research topic is termed plasma-based THz wave photonics in gas and liquid phases."In this paper,we review the most important experimental and theoretical works of the topic in the non-relativistic region with pump laser intensity below 1018 W/cm^(2).展开更多
文摘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.
文摘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.
基金supported by the National Basic Research Program of China (Grant No 2007CB310403)the Tianjin Municipal Primary application and Frontier Technology Research Plan,China (Grant No 07JCYBJC06200)
文摘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.
基金Supported by the National Natural Science Foundation of China (Grant Nos.11764038,11864037,11765018,and 91850209)。
文摘We theoretically investigate the characteristics of terahertz(THz) radiation from monolayer graphene exposed to normal incident few-cycle laser pulses, by numerically solving the extended semiconductor Bloch equations. Our simulations show that the THz spectra in low frequency regions are highly dependent on the carrier envelope phase(CEP) of driving laser pulses. Using an optimal CEP of few-cycle laser pulses, we can obtain broadband strong THz waves, due to the symmetry breaking of the laser-graphene system. Our results also show that the strength of the THz spectra depend on both the intensity and central wavelength of the laser pulses. The intensity dependence of the THz wave can be described by the excitation rate of graphene, while wavelength dependence can be traced back to the band velocity and the population of graphene. We find that a near single-cycle THz pulse can be obtained from graphene driven by a mid-infrared laser pulse.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61871355 and 61831012)the Talent Project of Zhejiang Provincial Department of Science and Technology(Grant No.2018R52043)the Research Funds for Universities of Zhejiang Province,China(Grant Nos.2020YW20 and 2021YW86)。
文摘We propose a novel metasurface based on a combined pattern of outer C-shaped ring and inner rectangular ring.By Fourier convolution operation to generating different predesigned sequences of metasurfaces,we realize various functionalities to flexible manipulate terahertz waves including vortex terahertz beam splitting,anomalous vortex terahertz wave deflection,vortex terahertz wave splitting and deflection simultaneously.The incident terahertz wave can be flexibly controlled in a single metasurface.The designed metasurface has an extensive application prospect in the field of future terahertz communication and sensing.
基金Supported by the National Basic Research Program of China under Grant No 2012CB933501the National Natural Science Foundation of China under Grant Nos 61177051,11304389,61404174 and 61205087
文摘We theoretically and numerically demonstrate that a transmission-type electrically tunable polarizer can be realized by using graphene ribbons supported on a dielectric film with a graphene sheet behind. The polarization mechanism originates from the antenna plasmon resonance of graphene stripes. The results of full-wave numerical simulations reveal that transmittance of 0.70 for one polarization and 0.0073 for another polarization can be obtained at normal incidence. The transmission-type electrically tunable polarizer provides and facilitates a variety of applications, including filtering, detecting, and imaging.
文摘In recent years, there has been increased interest in the terahertz waveband for application to ultra-high-speed wireless communications and remote sensing systems. However, atmospheric propagation at these wavelengths has a significant effect on the operational stability of systems using the terahertz waveband, so elucidating the effects of rain on propagation is a topic of high interest. We demonstrate various methods for calculating attenuation due to rain and evaluate these methods through comparison with calculated and experimental values. We find that in the 90 - 225 GHz microwave band, values calculated according to Mie scattering theory using the Best and P-S sleet raindrop size distributions best agree with experimental values. At 313 and 355 GHz terahertz-waveband frequencies, values calculated according to Mie scattering theory using the Weibull distribution and a prediction model following ITU-R recommendations best agree with experimental values. We furthermore find that attenuation due to rain increases in proportion to frequency for microwave-band frequencies below approximately 50 GHz, but that there is a peak at around 100 GHz, above which the degree of attenuation remains steady or decreases. Rain-induced attenuation increases in proportion to the rainfall intensity.
基金Project supported by the Open Foundation of Semiconductor Power Device Reliability Engineering Research Center of Ministry of Education, China (Grant No. ERCMEKFJJ2019-(05))the Natural Science Foundation of Guizhou University, China (Grant No. (2019)62)the China Scholarship Council (Grant No. 202106675002)。
文摘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.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10874020 and 11074025)the National Basic Research Program of China (Grant No. 2011CB922204)
文摘Based on coupled quantum dots, we present an interesting optical effect in a four-level loop coupled system. Both the two upper levels and the two lower levels are designed to be almost degenerate, which induces a considerable dipole moment. The terahertz wave is obtained from the low-frequency component of the photon emission spectrum. The frequency of the terahertz wave can be controlled by tuning the energy levels via designing the nanostructure appropriately or tuning the driving laser field. A terahertz wave with adjustable frequency and considerable intensity (100 times higher than that of the Rayleigh line) can be obtained. It provides an effective scheme for a terahertz source.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61735010,31671580,and 61601183)the Natural Science Foundation of Henan Province,China(Grant No.162300410190)the Program for Science&Technology Innovation Talents in Universities of Henan Province,China(Grant No.18HASTIT023)。
文摘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.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61735010,31671580,and 61601183)Natural Science Foundation of Henan Province,China(Grant No.162300410190)Program for Science&Technology Innovation Talents in Universities of Henan Province,China(Grant No.18HASTIT023)。
文摘A novel scheme for high-efficiency terahertz(THz)wave generation based on optimized cascaded difference frequency generation(OCDFG)with planar waveguide is presented.The phase mismatches of each-order cascaded difference frequency generation(CDFG)are modulated by changing the thickness of the waveguide,resulting in a decrement of phase mismatches in cascaded Stokes processes and an increment of phase mismatches in cascaded anti-Stokes processes simultaneously.The modulated phase mismatches enhance the cascaded Stokes processes and suppress the cascaded anti-Stokes processes simultaneously,yielding energy conversion efficiencies over 25%from optical wave to THz wave at 100 K.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61735010,31671580,and 61601183)the Natural Science Foundation of Henan Province,China(Grant No.162300410190)Program for Science&Technology Innovation Talents in Universities of Henan Province,China(Grant No.18HASTIT023)。
文摘High-efficiency terahertz(THz) wave generation with multiple frequencies by optimized cascaded difference frequency generation(OCDFG) is investigated at 100 K using a nonlinear crystal consisting of a periodically poled lithium niobate(PPLN) part and an aperiodically poled lithium niobate(APPLN) part.Two infrared pump waves with a frequency difference ω_(T1) generate THz waves and a series of cascaded optical waves in the PPLN part by cascaded difference frequency generation(CDFG).The generated cascaded optical waves with frequency interval ω_(T1) then further interact in the APPLN part by OCDFG,yielding the following two advantages.First,OCDFG in the APPLN part is efficiently stimulated by inputting multi-order cascaded optical waves rather than the only two intense infrared pump waves,yielding unprecedented energy conversion efficiencies in excess of 37% at 1 THz at 100 K.Second,THz waves with M timesω_(T1) are generated by mixing the mth-order and the(m+M)th-order cascaded optical waves by designing poling period distributions of the APPLN part.
基金Project supported by the National Basic Research Program of China(Grant No.2014CB340203)the National Natural Science Foundation of China(Grant Nos.61431010 and 61501350)the Natural Science Foundation of Shaanxi Province,China(Grant Nos.2018JM6016 and 2016JM1001)
文摘The propagation characteristics of oblique incidence terahertz(THz) waves through non-uniform plasma are investigated by the shift-operator finite-difference time-domain(SO-FDTD) method combined with the phase matching condition.The electron density distribution of the non-uniform plasma is assumed to be in a Gaussian profile. Validation of the present method is performed by comparing the results with those obtained by an analytical method for a homogeneous plasma slab.Then the effects of parameters of THz wave and plasma layer on the propagation properties are analyzed. It is found that the transmission coefficients greatly depend on the incident angle as well as on the thickness of the plasma, while the polarization of the incident wave has little influence on the propagation process in the range of frequency considered in this paper. The results confirm that the THz wave can pass through the plasma sheath effectively under certain conditions,which makes it a potential candidate to overcome the ionization blackout problem.
文摘Rain attenuation at 355.2 GHz in the terahertz wave range was measured with our new 355.2 GHz measuring system under rainfall intensities up to 25 mm/hr. Rain attenuation coefficients were also calculated using four raindrop-size distributions, e Marshall-Palmer (M-P), Best, Polyakova-Shifrin (P-S) and Weibull distributions, and using a specific rain attenuation model for prediction methods recommended by ITU-R. Measurements of a terahertz wave taken at 355.2 GHz were compared with our calculations. Results showed that the propagation experiment was in very good agreement with a calculation from a specific attenuation model for use in prediction method recommended by ITU-R.
基金supported by the National Natural Science Foundation of China (Grant No 10676110)the National Basic Research Program of China (Grant No 2007CB310401)
文摘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.
基金supported in part by the National Research Foundation, Prime Minister’s Office,Singapore under its Competitive Research Program (CRP Award No. NRF-CRP10-2012-04)in part by EDB, Singapore with grant No. S15-1322-IAF OSTIn-SIAG
文摘Manipulation of terahertz wave by metasurfaces has shown tremendous potential in developing compact and functional terahertz optical devices.Here,we propose complementary bilayer metasurfaces for enhanced terahertz wave amplitude and phase manipulation.The metasurfaces are composed of one layer of metal cut-wire arrays and one layer of their complementary aperture arrays separated by a dielectric spacer.Through the near-field coupling between transverse magnetic resonances in the metal apertures and electric resonances in the metal cut-wires,the structures can manipulate the cross polarization conversion and phase dispersion of terahertz wave.Particularly,the designed metasurfaces demonstrate a phase delay of 180°between two orthogonal axes with the same transmission amplitude between 0.70 and 1.0 THz,enabling a 45°broadband polarization conversion.When the metal cut-wires are rotated with respect to the apertures or the thickness of the dielectric spacer is changed,the amplitude and phase dispersion of the transmitted terahertz wave can be tuned.Such complementary coupled bilayer metasurfaces offer a new method to control the amplitude and phase dispersion of terahertz wave and promise great potential for applications in terahertz meta-devices.
文摘Terahertz (THz)-wave generation has been conducted based on difference frequency mixing (DFM) process with phonon-polariton excitation of ε-GaSe single crystals implemented with liquid-phase solution growth using the temperature difference method under controlled vapour pressure for the first time. The type-eoo phase matching condition for the DFM process at around 10 THz is satisfied by changing the incident angle into the crystal. The maximum conversion efficiency in the present DFG process is about 10-6?J-1?using a 0.1-mm-thick GaSe single crystal with the only ε- phase polytype, which can be greater than that of the commercially available Bridgman grown GaSe crystal including both ε- and γ-phase polytypes.
文摘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.
基金supported by the National Natural Science Foundation of China(NSFC)(Nos.62075157,62375199,and 62235013)the Tianjin Municipal Fund for Distinguished Young Scholars(No.20JCJQJC00190)the Key Fund of Shenzhen Natural Science Foundation(No.JCYJ20200109150212515)。
文摘In this Letter,we employ fused silica and two types of optical glass as examples to investigate the coherent terahertz(THz)wave emission from laser-ionized isotropic transparent dielectrics.Based on the laser energy and incident angle dependences,we ascribe the THz emission to the ponderomotive force-induced dipole oscillation.Additionally,our investigation on the dependence of THz amplitude on the laser pulse duration confirms the dominant role of avalanche ionization in solid dielectrics.The THz emission can be utilized to indirectly monitor the ultrafast dynamics of carrier generation and motion during the laser ionization process of solid dielectrics.
基金supported by the National Natural Science Foundation of China(Nos.62075157,61875151,and 62235013)Tianjin Municipal Fund for Distinguished Young Scholars(No.20JCJQJC00190)+3 种基金Key Fund of Shenzhen Natural Science Foundation(No.JCYJ20200109150212515)National Key Research and Development Program of China(No.2017YFA0701000)Prof.Xi-Cheng Zhang in The Institute of Optics at University of Rochester has support from the Air Force Office of Scientific Research(Nos.FA9550-21-1-0389 and FA9550-21-1-0300)the National Science Foundation(No.ECCS-2152081).
文摘Ultra-broadband,intense,coherent terahertz(THz)radiation can be generated,detected,and manipulated using laser-induced gas or liquid plasma as both the THz wave transmitter and detector,with a frequency coverage spanning across and beyond the whole THz gap."Such a research topic is termed plasma-based THz wave photonics in gas and liquid phases."In this paper,we review the most important experimental and theoretical works of the topic in the non-relativistic region with pump laser intensity below 1018 W/cm^(2).