The carrier dynamics of photoexcited electrons in the vicinity of the surface of (NH4)2S-passivated GaAs were studied via terahertz (THz) emission spectroscopy and optical-pump THz-probe spectroscopy. THz emission spectroscopy measurements, coupled with Monte Carlo simulations of THz emission, revealed that the surface electric field of GaAs reverses after passivation. The conductivity of photoexcited electrons was determined via optical-pump THz-probe spectroscopy, and was found to double after passivation. These experiments demonstrate that passivation significantly reduces the surface state density and surface recombination velocity of GaAs. Finally, we have demonstrated that passivation leads to an enhancement in the power radiated by photoconductive switch THz emitters, thereby showing the important influence of surface chemistry on the performance of ultrafast THz photonic devices.

In this paper, we present an optimal design of TE0n nonuniform ripple-wall mode converter in circular waveguide. The research work is based on the general coupled wave theory and numerical optimization method. The results of numerical calculation are in good agreement with those of simulation by HFSS. Compared with traditional TE0n mode converter of periodic waveguide perturbations, the TE0n nonuniform ripple-wall mode converter can achieve a high mode conversion efficiency with less corrugated periods. The length of the converter is shortened nearly by a half and the operating bandwidth with over 95% mode conversion is increased by 150%. The research work provides an important theoretical reference and a physics model for designing high power gyrotron mode converter with small axial size, wide operating bandwidth and high conversion efficiency.

Based on the main features of coolsmart fiber and the theory of knitted fabric structures， two structures of sports and leisure knitted fabrics with fast moisture absorption, description and anti-bacterial function are introduced in this article, detailing the selection of raw materials, pattern formation effect, the machine code organization and cam set out.

Based on the theory of sweat transfer principle and knitted fabric structure , two kinds of multi-functional fabrics are developed with chitin fiber , cotton fiber and coolplus fiber in this paper. The wearablity , moisture-absorption and dry-fast property , air permeability and anti-bacterial property etc. are tested . The results show that the fabrics have many excellent properties , such as wearablity , moisture-absorption , dry-fast and anti-bacterial property etc. The fabrics can absorb moisture rapidly from one side of the fabric , then transfer it to the other side of the fabric and gave off , thus the fabrics can dry quickly . So the clothing made of these fabrics will keep our skin dry and comfortable, In summary , the fabrics developed are ideal fabrics for making high–quality leisure sportswear .

The discrete metallic-pole-planar slow wave structure (SWS) is introduced in this paper, and the high frequency characteristics are studied. And procedures based on three-dimensional finite-difference time-domain (3-D FDTD) arithmetic are used to calculate the dispersive characteristics of the new SWS, and HFSS simulation software is used to analyze the coupling impedance. Results show the high frequency characteristics of the pole structure not only have a general similarity in comparison with these of the grating, but also have itself advantages. For the electrons moving between multiple poles of the structure, the interaction impedances are symmetry; relatively thick electron beams can efficiently interact with the high-frequency field while it used as the high frequency system of vacuum electronic devices. This kind of SWS is promising to lower the starting current density and have better efficiency than the traditional grating SWS. According to the results, a sub-millimeter radiation source driven by the multiple beams can be designed at a low operating current density.