光学变换中的离散取样方法

本文研究了光学变换中的离散取样问题。基于幺正变换的考虑,求得了光学变换中离散取样方法所依据的条件。导出了包含取样单元透光孔作用的光传播矩阵。最后,以自然序Walsh变换为例,具体计算了变换所需全息透镜的振幅与相位分布及相应的误差。 关键词：     

Influence of the channel electric field distribution on the polarization Coulomb field scattering in In0.18Al0.82N/AIN/GaN heterostructure field-effect transistors

By making use of the quasi-two-dimensional （quasi-2D） model, the current-voltage （l-V） characteristics of In0AsA10.82N/A1N/GaN heterostructure field-effect transistors （HFETs） with different gate lengths are simulated based on the measured capacitance-voltage （C-V） characteristics and I-V characteristics. By analyzing the variation of the electron mobility for the two-dimensional electron gas （2DEG） with electric field, it is found that the different polarization charge distributions generated by the different channel electric field distributions can result in different polarization Coulomb field scatterings. The difference between the electron mobilities primarily caused by the polarization Coulomb field scatterings can reach up to 1522.9 cm2/V.s for the prepared In0.38AI0.82N/A1N/GaN HFETs. In addition, when the 2DEG sheet density is modulated by the drain-source bias, the electron mobility presents a peak with the variation of the 2DEG sheet density, the gate length is smaller, and the 2DEG sheet density corresponding to the peak point is higher.     

一种光路自准方法

在光学实验中,经常遇到的一个课题是如何把各光学元件调节到它们的正确位置上,借助于机械轨道。经纬仪和可调焦平行光管等光学仪器进行位置调节是常用的方法.本文基于光栅在光路中的衍射作用和杨氏双缝干涉现象,提出了一种光路自准方法.它已成功地应用于光学Walsh变换[1]实验中.在这个实验中曾经设想和试用过多种调节手段。企图把各全息透镜调节到它们的正确位置上,由于调节仪器的光轴与实验光路的光轴很难保持一致,以致效果不甚理想.对于光路自准方法,调节光路就是实验光路,即在光路系统中传播的光波既是调节用光波又是实验用光波,二者是…     

用扫描曝光法制作相息图

用扫描曝光法制作相息图与抽样曝光法相比具有可以连续取样和设备简单的优点。本文提出了一种扫描曝光的方案,其扫描mask的开孔长度不受成象系统的限制。它适用于可以进行变量分离的Kinoform型元件。     

Influence of the channel electric field distribution on the polarization Coulomb field scattering in In0.18 Al0.82 N/AlN/GaN heterostructure field-effect transistors

By making use of the quasi-two-dimensional(quasi-2D) model, the current–voltage(I–V) characteristics of In0.18Al0.82N/AlN/GaN heterostructure field-effect transistors(HFETs) with different gate lengths are simulated based on the measured capacitance–voltage(C–V) characteristics and I–V characteristics. By analyzing the variation of the electron mobility for the two-dimensional electron gas(2DEG) with electric field, it is found that the different polarization charge distributions generated by the different channel electric field distributions can result in different polarization Coulomb field scatterings. The difference between the electron mobilities primarily caused by the polarization Coulomb field scatterings can reach up to 1522.9 cm2/V·s for the prepared In0.18Al0.82N/AlN/GaN HFETs. In addition, when the 2DEG sheet density is modulated by the drain–source bias, the electron mobility presents a peak with the variation of the 2DEG sheet density,the gate length is smaller, and the 2DEG sheet density corresponding to the peak point is higher.     

Electron mobility in the linear region of an AlGaN/AlN/GaN heterostructure field-effect transistor

We simulate the current-voltage （I-V） characteristics of AlGaN/AlN/GaN heterostructure field-effect transistors （HFETs） with different gate lengths using the quasi-two-dimensional （quasi-2D） model. The calculation results obtained using the modified mobility model are found to accord well with the experimental data. By analyzing the variation of the electron mobility for the two-dimensional electron gas （213EG） with the electric field in the linear region of the AlGaN/AlN/GaN HFET I-V output characteristics, it is found that the polarization Coulomb field scattering still plays an important role in the electron mobility of AlGaN/AlN/GaN HFETs at the higher drain voltage and channel electric field. As drain voltage and channel electric field increase, the 2DEG density reduces and the polarization Coulomb field scattering increases, as a result, the 2DEG electron mobility decreases.     

溶剂浮选法分离富集大黄中的有效成分

采用溶剂浮选法对大黄提取液中的芦荟大黄素、大黄素、大黄酚以及大黄素甲醚进行了分离富集,并用高效液相色谱法分别测定了其含量。考察了料液浓度、浮选溶剂、浮选时间、浮选液pH值、氮气流速和电解质NaCl浓度对浮选效率的影响,并与泡沫浮选法和溶剂萃取法进行了比较。结果表明：溶剂萃取效果最差,泡沫浮选次之,溶剂浮选法分离富集效果最好。当料液浓度为6．4mg／mL,浮选时间为30min,浮选液pH一1～2,氮气流速为20mL／min,电解质NaCl浓度为0．4mol／L时,溶剂浮选效率最佳。     

光学一般变换的傅里叶变换实验方法

本文利用傅里叶光学系统简化了光学一般变换全息透镜的设计,以一维八序Walsh-Hadamard变换为例,用计算机设计和产生了变换所需的透镜,并进行引了光学实验,得到了预定变换结果。     

光学相位滤波器的发展及其应用

一、引 言 近年来,随着各种新技术的出现和材料科学的发展,光学滤波器的种类不断增加[1],特别是光学相位滤波器发展尤为迅速。应用范围也随之更加广泛.所谓光学相位滤波器就是对入射光波进行相位调制的元件.虽然从广义上来说诸如透镜、棱镜等光学元件都可以视为相位滤波器,但是     

光学信息处理讲座第四讲 银盐记录介质在光学信息处理中的应用

光学信息处理以其速度快、信息容量大、结构简单、可以同时完成二维或多通道运算等优点而被人们所重视,并已成为现代光学的重要组成部分.光学信息处理的基本装置可以分为以下几个主要部分:光源、输入转换器、光学处理系统以及输出转换器.目前,输入转换器主要通过感光胶片将输入信号或图象送入处理系统.光学处理系统是由透镜或其它全息光学元件构成的模拟运算系统,此系统中的空间滤波器是光学信息处理系统中的关键元件,必须根据具体课题的要求进行设计并用记录介质或其它材料来制备.输出转换器一般是用记录介质把处理结果记录下来,或通过摄像…