Using an excitonic basis, we investigate the intraband polarization, optical absorption spectra, and terahertzemission of semiconductor superlattice with the density matrix theory. The excitonic Bloch oscillation is d...Using an excitonic basis, we investigate the intraband polarization, optical absorption spectra, and terahertzemission of semiconductor superlattice with the density matrix theory. The excitonic Bloch oscillation is driven by thedc and ac electric fields. The slow variation in the intraband polarization depends on the ac electric field frequency. Theintraband polarization increases when the ac electric field frequency is below the Bloch frequency. When the ac electricfield frequency is above the Bloch frequency, the intraband polarization downwards and its intensity decreases. Thesatellite structures in the optical absorption spectra are presented. Due to excitonic dynamic localization, the emissionlines of terahertz shift in different ac electric field and dc electric field.展开更多
The generation of terahertz （THz） emission from air plasma induced by two-color femtosecond laser pulses is studied on the basis of a transient photocurrent model. While the gas is ionized by the two-color femtoseco...The generation of terahertz （THz） emission from air plasma induced by two-color femtosecond laser pulses is studied on the basis of a transient photocurrent model. While the gas is ionized by the two-color femtosecond laser-pulses com- posed of the fundamental and its second harmonic, a non-vanishing directional photoelectron current emerges, radiating a THz electromagnetic pulse. The gas ionization processes at three different laser-pulse energies are simulated, and the corresponding THz waveforms and spectra are plotted. The results demonstrate that, by keeping the laser-pulse width and the relative phase between two pulses invariant when the laser energy is at a moderate value, the emitted THz fields are significantly enhanced with a near-linear dependence on the optical energy.展开更多
We report the growth of a-plane InN on an r-plane sapphire substrate by plasma-assisted molecular-beam epitaxy. It is found that the a-plane InN is successfully grown by using a CaN buffer layer, which has been confir...We report the growth of a-plane InN on an r-plane sapphire substrate by plasma-assisted molecular-beam epitaxy. It is found that the a-plane InN is successfully grown by using a CaN buffer layer, which has been confirmed by reflection high-energy electron diffraction, x-ray diffraction and Raman scattering measurements. The Hall effect measurement shows that the electron mobility of the as-grown a-plane InN is about 406 cm^2/V·s with a residual electron concentration of 5.7 × 10^18 cm^-3. THz emission from the a-plane InN film is also studied, where it is found that the emission amplitude is inversely proportional to the conductivity.展开更多
An efficient ammonia terahertz （THz） cavity laser is reported experimentally. Unlike the past design schemes such as hole couplers and freestanding mesh couplers, in our systems the input and output couplers are fab...An efficient ammonia terahertz （THz） cavity laser is reported experimentally. Unlike the past design schemes such as hole couplers and freestanding mesh couplers, in our systems the input and output couplers are fabricated by depositing nickel capacitive metallic meshes on ZnSe and high-resistivity silicon substrates. Thus the couplers not only can be constructed as an F-P oscillator but also can be used as sealed windows that are easier to perform the adjustment of alignment with. To enhanceTHz laser output energy and photon conversion efficiency, the dominant factors such as pump intensity and gas pressure are investigated experimentally. Finally, a 1.35mJ terahertz radiation of ammonia laser with 90μm wavelength （3.33THz） operating at 1.09kPa pumped by a 402mJ TEA CO2 laser with 9R （16） line is generated, and photon conversion efficiencies of 6.5% are achieved.展开更多
A 30-MeV femto-second electron linac is built at the Shanghai Institute of Applied Physics, which can produce high power, coherent THz undulator radiation. We report the experimental facility and measurement of the po...A 30-MeV femto-second electron linac is built at the Shanghai Institute of Applied Physics, which can produce high power, coherent THz undulator radiation. We report the experimental facility and measurement of the power, frequency spectrum. First experiments show the averaged power at THz to be about 20mW.展开更多
We experimentally investigate the terahertz （THz） generation from a graphite surface induced by femtosecond laser pulses, and systematically study the dependence on the excitation power, the crystal orientation of g...We experimentally investigate the terahertz （THz） generation from a graphite surface induced by femtosecond laser pulses, and systematically study the dependence on the excitation power, the crystal orientation of graphite, polarization state and incident angle of optical beam. New evidence related to excitation and detection geometry is found and presented, which supports the THz generation mechanism of transient photocarrier transporting along the basal plane normal. Our observation also suggests other probable contributions by in-plane charge oscillations. The results may be helpful to explore and understand the photoelectric properties of graphite and other allotropes of carbon.展开更多
欧洲2002国际磁学会议(IntermagEurope2002)于2002年4月28日～5月2日在荷兰阿姆斯特丹RAI会议中心举行。此次会议由国际IEEE电气与电气工程师协会磁性分会(Magnetics Society of the Institute of Electrical and Electrical Engineerin...欧洲2002国际磁学会议(IntermagEurope2002)于2002年4月28日～5月2日在荷兰阿姆斯特丹RAI会议中心举行。此次会议由国际IEEE电气与电气工程师协会磁性分会(Magnetics Society of the Institute of Electrical and Electrical EngineeringIEEE)举办,来自世界各地的大学和公司800多人参加了此次会议。会议主要讨论了磁性物理、材料、应用的研究进展和发展方向。展开更多
基金Supported by National Science Foundation of China under Grant No.10647132the Scientific Research Fund of Hunan Provincial Education Department under Grant No.05B014
文摘Using an excitonic basis, we investigate the intraband polarization, optical absorption spectra, and terahertzemission of semiconductor superlattice with the density matrix theory. The excitonic Bloch oscillation is driven by thedc and ac electric fields. The slow variation in the intraband polarization depends on the ac electric field frequency. Theintraband polarization increases when the ac electric field frequency is below the Bloch frequency. When the ac electricfield frequency is above the Bloch frequency, the intraband polarization downwards and its intensity decreases. Thesatellite structures in the optical absorption spectra are presented. Due to excitonic dynamic localization, the emissionlines of terahertz shift in different ac electric field and dc electric field.
基金Project supported by the National Natural Science Foundation of China (Grant No.61177095)the Natural Science Foundation of Hubei Province,China(Grant No.2012FFA074)+1 种基金the Ph.D.Programs Foundation of Ministry of Education of China (Grant No.20100142110042)the Fundamental Research Funds for the Central Universities (Grant Nos.2012QN094 and 2012QN097)
文摘The generation of terahertz （THz） emission from air plasma induced by two-color femtosecond laser pulses is studied on the basis of a transient photocurrent model. While the gas is ionized by the two-color femtosecond laser-pulses com- posed of the fundamental and its second harmonic, a non-vanishing directional photoelectron current emerges, radiating a THz electromagnetic pulse. The gas ionization processes at three different laser-pulse energies are simulated, and the corresponding THz waveforms and spectra are plotted. The results demonstrate that, by keeping the laser-pulse width and the relative phase between two pulses invariant when the laser energy is at a moderate value, the emitted THz fields are significantly enhanced with a near-linear dependence on the optical energy.
基金Supported by the National Basic Research Program of China under Grant No 2012CB619300, the National Natural Science Foundation of China under Grant Nos 61225019, 11023003 and 61376060, and the National High-Technology Research and Devel- opment Program of China under Grant No 2011AA050514.
文摘We report the growth of a-plane InN on an r-plane sapphire substrate by plasma-assisted molecular-beam epitaxy. It is found that the a-plane InN is successfully grown by using a CaN buffer layer, which has been confirmed by reflection high-energy electron diffraction, x-ray diffraction and Raman scattering measurements. The Hall effect measurement shows that the electron mobility of the as-grown a-plane InN is about 406 cm^2/V·s with a residual electron concentration of 5.7 × 10^18 cm^-3. THz emission from the a-plane InN film is also studied, where it is found that the emission amplitude is inversely proportional to the conductivity.
文摘An efficient ammonia terahertz （THz） cavity laser is reported experimentally. Unlike the past design schemes such as hole couplers and freestanding mesh couplers, in our systems the input and output couplers are fabricated by depositing nickel capacitive metallic meshes on ZnSe and high-resistivity silicon substrates. Thus the couplers not only can be constructed as an F-P oscillator but also can be used as sealed windows that are easier to perform the adjustment of alignment with. To enhanceTHz laser output energy and photon conversion efficiency, the dominant factors such as pump intensity and gas pressure are investigated experimentally. Finally, a 1.35mJ terahertz radiation of ammonia laser with 90μm wavelength （3.33THz） operating at 1.09kPa pumped by a 402mJ TEA CO2 laser with 9R （16） line is generated, and photon conversion efficiencies of 6.5% are achieved.
文摘A 30-MeV femto-second electron linac is built at the Shanghai Institute of Applied Physics, which can produce high power, coherent THz undulator radiation. We report the experimental facility and measurement of the power, frequency spectrum. First experiments show the averaged power at THz to be about 20mW.
基金Supported by the National Basic Research Program of China under Grant No 2014CB339800, and the National Natural Science Foundation of China under Grant Nos 11374358 and 61077082.
文摘We experimentally investigate the terahertz （THz） generation from a graphite surface induced by femtosecond laser pulses, and systematically study the dependence on the excitation power, the crystal orientation of graphite, polarization state and incident angle of optical beam. New evidence related to excitation and detection geometry is found and presented, which supports the THz generation mechanism of transient photocarrier transporting along the basal plane normal. Our observation also suggests other probable contributions by in-plane charge oscillations. The results may be helpful to explore and understand the photoelectric properties of graphite and other allotropes of carbon.
文摘欧洲2002国际磁学会议(IntermagEurope2002)于2002年4月28日～5月2日在荷兰阿姆斯特丹RAI会议中心举行。此次会议由国际IEEE电气与电气工程师协会磁性分会(Magnetics Society of the Institute of Electrical and Electrical EngineeringIEEE)举办,来自世界各地的大学和公司800多人参加了此次会议。会议主要讨论了磁性物理、材料、应用的研究进展和发展方向。
