A proposed approach for detecting terahertz pulses by using double few-cycle laser pulses with opposite carrier envelope phases

Previous research shows that few-cycle laser(FCL) pulses with low energy and without a bias field can be used to coherently detect terahertz(THz) pulses. As we know, it is very difficult to stabilize the carrier envelope phase(CEP) of FCL pulses, i.e., there are some random fluctuations for the CEP. Here we theoretically investigate the influence of such instability on the accuracy of THz detection. Our results show that although there is an optimum CEP for THz detection, the fluctuations of the CEP will lead to terrible thorns on the detected THz waveform. In order to solve this problem, we propose an approach using two few-cycle laser pulses with opposite CEPs, i.e., their CEPs are differed by π.     

金属网栅法布里珀罗干涉仪测量太赫兹波波长

设计并制作了用于测量波长大于150 μm(频率低于2 THz)的太赫兹波波长的金属网栅法布里珀罗干涉仪(FPI)。采用光电子微纳制造工艺制作了五组周期不大于40 μm,线宽不大于10 μm的有衬底方形金属网栅,利用太赫兹时域光谱技术测量了金属网栅的太赫兹波段光电特性,得到了各组金属网栅在感兴趣频段的反射率和金属网栅FPI的反射精细度,结果表明所制作的金属网栅FPI均可用于测量波长大于150 μm的太赫兹波。实验搭建金属网栅FPI扫描测量了212 μm的太赫兹波波长,与理论结果吻合。研究了金属网栅FPI对太赫兹波偏振方向的依赖性以及对FPI腔镜平行度的要求,结果表明,方形金属网栅FPI对正入射太赫兹波偏振方向不敏感,而对FPI腔镜平行度很敏感。     

有外加电源的串联光折变晶体回路中的独立空间全息-哈密顿屏蔽孤子对

在由两块垂直于光轴两端面镀上电极的光折变晶体和一个外加电源组成的串联光折变晶体回路中, 在适当的条件下可以形成独立空间全息-哈密顿屏蔽孤子对. 这种孤子对共有四种类型:明-明、暗-暗、明-暗以及暗-明. 当入射光束的空间展宽尺寸远小于晶体宽度时, 孤子对中的哈密顿暗孤子可以通过光感应电流影响另一个孤子, 而哈密顿明孤子和全息孤子则不能影响另一孤子.     

Transverse effects in photorefractive two-wave mixing

In a biased photorefractive crystal, the process of two one-dimensional waves mixing, i.e., the dynamical evolution of both pump beam and signal beam, is traced by numerically solving the coupled-wave equation. Direct simulations show that the propagation and stability of the two beams are completely determined by the system parameters, such as the external bias field, the intensity and the beam waist of the pump beam. By adjusting these parameters, one can control the state of two Gaussian waves mixing. The numerical results are helpful for performing a two-wave mixing experiment.     

The dependence on optical energy of terahertz emission from air plasma induced by two-color femtosecond laser-pulses

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.     

有外加电源的串联光折变晶体回路中的独立空间全息-哈密顿屏蔽孤子对

在由两块垂直于光轴两端面镀上电极的光折变晶体和一个外加电源组成的串联光折变晶体回路中, 在适当的条件下可以形成独立空间全息-哈密顿屏蔽孤子对. 这种孤子对共有四种类型:明-明、暗-暗、明-暗以及暗-明. 当入射光束的空间展宽尺寸远小于晶体宽度时, 孤子对中的哈密顿暗孤子可以通过光感应电流影响另一个孤子, 而哈密顿明孤子和全息孤子则不能影响另一孤子.     

MEASUREMENTS OF 129Xe NUCLEAR MAGNETIC RESONANCE IN GASEOUS, LIQUID AND SOLID XENON

Natural xenon, contained in a ceil at a pressure of 6.5 atm, is frozen from 303 to 137 K on an WP-80SY NMR spectrometer. NMR signals of ¹²⁹Xe atoms in gaseous, liquid and solid phases are measured at various temperatures, We found that the chemical shift of NMR signal of liquid ¹²⁹Xe (expressed as ΔH) is directly proportional to the density of the sample with a coefficient of (4.73±0.05)×10^-7; and the chemical shift of NMR signal of solid ¹²⁹Xe (expressed as ΔH) is nearly proportional to the density of the sample with a coefficient of (5.00±0.08)×10^-7.     

MEASUREMENTS OF 129Xe NUCLEAR MAGNETIC RESONANCE IN GASEOUS,LIQUID AND SOLID XENON

Natural xenon, contained in a ceil at a pressure of 6.5 atm, is frozen from 303 to 137 K on an WP-80SY NMR spectrometer. NMR signals of ¹²⁹Xe atoms in gaseous, liquid and solid phases are measured at various temperatures, We found that the chemical shift of NMR signal of liquid ¹²⁹Xe (expressed as ΔH) is directly proportional to the density of the sample with a coefficient of (4.73±0.05)×10^-7; and the chemical shift of NMR signal of solid ¹²⁹Xe (expressed as ΔH) is nearly proportional to the density of the sample with a coefficient of (5.00±0.08)×10^-7.     

射频激励二氧化碳激光器功率控制电路原理及设计

所叙述的二氧化碳激光器内部的基本结构。包括功率控制器、射频电路等。通过对功率控制部分的研制使激光器的生产逐步实现国产化。用单片机控制电路的PWM的开关、放大、检测，将放大后的PWM送至射频激励，控制射频电路中的射频信号，从而控制激光器输出光功率的大小。     

Theoretical investigation of tunable polarized broadband terahertz radiation from magnetized gas plasma

The mechanism of terahertz(THz) pulse generation with a static magnetic field imposed on a gas plasma is theoretically investigated. The investigation demonstrates that the static magnetic field alters the electron motion during the optical field ionization of gas, leading to a two-dimensional asymmetric acceleration process of the ionized electrons. Simulation results reveal that elliptically or circularly polarized broadband THz radiation can be generated with an external static magnetic field imposed along the propagation direction of the two-color laser. The polarization of the THz radiation can be tuned by the strength of the external static magnetic field.