Electron spin lifetimes in Hg0.78Cd0.22 Te and InSb

We have made direct pump–probe measurements of spin lifetimes in long wavelength narrow-gap semiconductors at wavelengths between 4 and 10 μm and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes, τ_s300 ps, even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that τ_s is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of τ_s in non-degenerate lightly n-type Hg_0.78Cd_0.22Te of approximately the same band gap as InSb, and find that τ_s varies from 356 ps at 150 K to 24 ps at 300 K. Our results, both in magnitude and temperature dependence of τ_s, imply that the Elliott–Yafet model dominates in these materials.     

Light Diffraction of Aligned Polymer Fibers Periodically Dispersed by Phase Separation of Liquid Crystal and Polymer

We have confirmed light diffraction of aligned polymer fibers obtained by a phase separation of an anisotropic-phase solution of liquid crystal and polymer. He—Ne laser light passing through the polymer fibers was scattered in the axis vertical to the fibers, and had two peaks of light intensity symmetrical to the center of the transmitting laser spot. The two peaks were found to be caused by light diffraction due to the periodic polymer-fiber dispersion because the peaks corresponded to values calculated by intervals between the fibers. The periodical fiber networks are considered to be formed by anisotropic spinodal decomposition. This effect can be used to measure the dispersion order of the polymer fibers. © 2004 The Optical Society of Japan     

Measurements of Time-Varying Characteristics of Optical Signals and Inhomogeneities of Tested Substances with Additional Phase Modulation

The problem of investigation of the amplitude and phase structure of a time-varying probing optical signal and the structure of time-varying inhomogeneities of a substance tested by this signal is considered. The analysis is concerned, in particular, with determination of the structure of signals and processes with resolution in the pico- and femtosecond range. The scheme used for the analysis is based on registration of four spatially separated spectra of the studied radiation. The spectra are formed in a four-channel scheme with a twin-wave Michelson interferometer and a spectral device. Modulators based on electrooptical crystals (perovskites) are placed in the channels. The sum spectra are formed: without modulators, with the effect of either of the modulators, and with both of them affecting the radiation. The effect of the studied substance implies either modulating the radiation (in this case it is described by multiplication) or redistributing the radiation (then it is described by convolution).     

Completely biodegradable composites of poly(propylene carbonate) and short,lignocellulose fiber Hildegardia populifolia

The composites of biodegradable poly(propylene carbonate) (PPC) reinforced with short Hildegardia populifolia natural fiber were prepared by melt mixing followed by compression molding. The mechanical properties, thermal properties, and morphologies of the composites were studied via static and dynamic mechanical measurements, thermogravimetric analysis, and scanning electron microscopy (SEM) techniques, respectively. Static tensile tests showed that the stiffness and tensile strength of the composites increased with an increasing fiber content. However, the elongation at break and the energy to break decreased dramatically with the addition of short fiber. The relationship between the experimental results and the compatibility or interaction between the PPC matrix and fiber was correlated. SEM observations indicated good interfacial contact between the short fiber and PPC matrix. Thermogravimetric analysis revealed that the introduction of short Hildegardia populifolia fiber led to a slightly improved thermooxidative stability of PPC. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 666–675, 2004     

光参量啁啾脉冲饱和放大的增益稳定性

 光参量啁啾脉冲放大（OPCPA）在饱和放大区存在一个增益稳定点，据此设计了一个输出稳定的三级OPCPA系统；第一、二、三级分别选用准相位匹配的周期极化钛氧磷酸钾（PPKTP）晶体、LBO晶体和KDP晶体作为增益介质。饱和放大时，增益随泵浦光强度变化时的增益输出稳定性明显改善，在泵浦光强度抖动低于6%的情况下，各级光参量放大器OPA输出的增益抖动小于1%。前级采用准相位匹配的PPKTP晶体作为增益介质，在远低于破坏阈值的30MW/cm²的泵浦功率密度下，可得到2×10⁵的饱和放大增益和20%的能量转换效率。     

光纤光栅选频掺Yb3+双包层光纤激光器

利用相位掩模法 ,在D形内包层掺Yb3 双包层光纤一端直接写制出Bragg光栅 ,用作双包层光纤激光器的输出腔镜 .试验得到了线宽为 0 196nm ,波长为 10 5 8 2nm ,最高输出功率为 5 70mW的稳定激光输出 ,解决了激光器中模式竞争造成的输出不稳定现象 .从速率方程出发 ,对激光器的输出功率与抽运功率、光栅反射率的关系以及最佳光纤长度进行了理论分析 ,结果与实验符合很好     

闪烁光纤在γ射线辐照下部分特性的蒙特卡罗模拟

 闪烁光纤在射线成像方面的应用越来越广泛。为了进一步了解闪烁光纤在射线辐照下的基本特性，基于蒙特卡罗方法，利用计算机模拟分析了γ射线在闪烁光纤中的好事例率与光纤长度及射线能量的关系，能量沉积效率与光纤长度及射线能量的关系。此项工作对于闪烁光纤阵列在射线成像，剂量场测量等方面的研究很有价值。     

用楔形柱面光纤微透镜耦合的1.3μm SOA组件

运用激光模式耦合理论分析了半导体光放大器(SOA)与单模通信光纤的连接损耗,并设计制作了楔形柱面光纤微透镜用来实现两者的模斑匹配,有效地降低了器件的光耦合损耗.本文介绍了楔形柱面光纤微透镜耦合的1.3 μm半导体光放大器(SOA)组件及其制作方法.该组件的最大增益不小于14 dB,其偏振灵敏度小于1 dB,增益波动不大于0.5 dB.     

Electromagnetic energy flow near nanoparticles—I: single spheres

The electromagnetic (EM) energy flow near single spheres is investigated by applying Mie theory. From the patterns of the energy flow, the absorption and the scattering of light can be understood in the microscopic point of view. In the absorption profiles of metallic particles, most absorbed energy is consumed on the surface of the particles, which indicates that the resonance of surface plasmon is different from that of the bulk plasmon. Two mechanisms to enhanced local EM field are also distinguished. One is the surface plasmon resonance, and another one is the intensified energy flow.     

两段级联掺铒光纤放大器的优化研究

基于Giles模型,研究了980 nm和1480 nm泵浦的两段级联掺铒光纤放大器(EDFA)的设计,得出了掺铒光纤(EDF)的最佳长度和光隔离器的最佳位置随泵浦功率和信号功率的变化关系.比较980 nm和1480 nm泵浦的两段级联EDFA,可以发现,前者的最佳EDF长度短,而光隔离器最佳位置距EDFA输入端远.