Electrical and optical properties of GexFexSe100−2x chalcogenide thin films

Optical absorption at room temperature and electrical conductivity at temperatures between 283 and 333 K of vacuum evaporated Ge_xFe_xSe_100−2x (0≤x≤15) amorphous thin films have been studied as a function of composition and film thickness. It was found that the optical absorption is due to indirect transition and the energy gap increases with increasing both Ge and Fe content; on the other hand, the width of the band tail exhibits the opposite behavior. The optical band gap E_opt was found to be almost thickness independent. The electrical conductivity show two types of conduction, at higher temperature the conduction is due to extended states, while the conduction at low temperature is due to variable range hopping in the localized states near Fermi level. Increasing Ge and Fe contents were found to decrease the localized state density N(E_F), electrical conductivity and increase the activation energy for conduction, which is nearly thickness independent. Variation of the atomic densities ρ, molar volume V, glass transition temperature T_g cohesive energy C.E and number of constraints N_Co with average coordination number Z was investigated. The relationship between the optical gap and chemical composition is discussed in terms of the cohesive energy C.E, average heat of atomization and coordination numbers.     

OH impurities in co-doped LiNbO3:Cr :ZnO congruent crystals

Infrared optical absorption has been used to study OH⁻impurities into congruent co-doped LiNbO₃:Cr³⁺:ZnO crystals doped with different Zn²⁺ concentration. The OH⁻ IR absorption spectra present three bands that can be associated with different OH⁻ complex centres available in the lattice. For crystals with lower Zn²⁺ concentrations (<4.7%) only one IR absorption band centred at 2867 nm (3490 cm⁻¹) is reported which is associated with the OH⁻ unperturbed vibration. For crystals with higher Zn²⁺ concentrations (>4.7%), two new bands associated with OH⁻vibration in distortion environment are reported. These bands are centred at 2827 nm (3537 cm⁻¹) and 2847 nm (3512 cm⁻¹) and can be associated with OH⁻-Zn²⁺ and Cr³⁺(Li⁺)-OH⁻-Zn²⁺(Int.) complex centres, respectively. Electron paramagnetic resonance (EPR) has been used to identify the Cr³⁺ centres in the lattice of the doped LiNbO₃:ZnO crystals.     

光象散法测量溶液浓度的研究

本文报道一种用光象散技术测量溶液浓度的新方法。给出其理论解析、测量原理、系统构成与实验结果。从理论研究与初步实验结果表明,本方法用于自动测量溶液浓度有好的可行性与实用性,亦可作为在线监测。     

Implementation of an algorithm for detecting patterns in defocused scenes using binary joint transform correlation

An original method to detect images in defocused scenes by means of a binary joint transform correlation is presented. Defocused images are described in frequency domain as the product between the Fourier transform of the in-focus scene by the optical transfer function of the imaging lens. This function, which presents positive and negative values, introduces sign errors in the joint power spectrum. The goal of this study is to detect the sign of the optical transfer function starting from the defocused image by means of a digital algorithm. Information provided by the algorithm allows to compensate the sign errors in the binary joint power spectrum and to obtain invariant correlations with respect to defocusing. Theoretical analysis and digital experiments to test the procedure are provided.     

Fiber Optical Bragg Grating Refractometer

We have demonstrated an evanescent field refractive indexfiber sensor comprising a 42-mm Bragg grating in an etched fiber together with a tunable Distributed Bragg Reflector (DBR) laser. Characterization of different aqueous sucrose solutions resulted in a resolution of roughly 10 mM sucrose. The sensor in the presented form has a theoretical sensitivity of higher than 10 5 refractive index unit (riu) in a refractive index region close to the cladding index of the fiber. However, the technique allows for an even higher sensitivity than 10 6 riu with a proper signal processing scheme.     

Geometric-optical reconstruction of a wavefront experimental realization with femtosecond laser pulses

The mechanism of wavefront reconstruction by geometric-optical reflection of reconstruction radiation from surfaces with constant phase differences between the object and reference waves has been investigated. The main difference between this mechanism and a holographic one is the absence of diffraction of the reconstructing radiation by the periodic structure and as a consequence the achromatism of the reconstruction process. Incoherent continuous radiation and ultrashort laser pulses were used in the experiments. The effect of achromatic reconstruction has been obtained after recording the interference of counterpropagating 30–40 fs pulses from an Al₂O₃:Ti³⁺ laser in bulk media.     

二自由度反射式光纤传感探头的结构设计

采用五光纤特殊排列方式,研制了全自动补偿光纤二自由度传感探测器.分析了二自由度的探测方法,给出了可能的结构排列方案.理论上,给出了探测响应函数,与实验结果进行了对比.可用于二自由度非接触测量场合。     

光测仪器的轴系检测及数据处理

本文针对光测仪器的轴系检测提出了一种新的改进方法,该方法采用数字式电子水平仪测量垂直轴系的径向晃动量;并用不等间隔采样点的最小二乘法计算垂直轴系、水平轴系的晃动误差。该方法及计算程序已成功地应用于多项任务的轴系误差测量中。     

光交叉连接节点的功能结构

光交叉连接(OXC)是未来波分复用光传送网实现交换与选路功能的核心部件.目前,OXC节点的物理结构得到深入研究,已经提出了一些采用不同光子器件的OXC实现方案.本文从描述光交叉连接功能的角度出发,给出一种分析OXC节点功能结构的模型,并比较各种OXC方案在功能结构上的差异。     

Ellipsometric spectroscopy study of photoluminescent Si/SiO2 systems obtained by magnetron co-sputtering

Si nanograins embedded in silica matrix were obtained by magnetron cosputtering of both Si and SiO₂ at different substrate temperature (200–700°C) and thermal annealing at 1100°C. The samples were characterized by ellipsometric spectroscopy, high-resolution electron microscopy observations and photoluminescence. The highest excess of Si atoms was found to be incorporated for deposition temperature near 400–500°C, giving rise to a maximum PL and a shift of the peak position towards lower energy. These features might be interpreted in terms of quantum size effects and of density of grains, even though the interface states seem to be involved in the improvement of the photoluminescence efficiency.