Interferometrie a grande difference de marche en lumiere blanche

A new method for measuring the visibility of the spectral modulation in an interferometry experiment where the path difference is made much larger than the coherence length has been described recently. A measure of the visibility of the spectral modulation using a white light source over a path difference up to 10.7 meters is reported.     

Resolution and visibility of two-color pseudothermal lensless ghost imaging

Two-color (or nondegenerate-wavelength) lensless ghost imaging using pseudothermal light source is investigated theoretically by use of classical optical coherence theory. We find that for two-color pseudothermal lensless ghost imaging the visibility and resolution is determined by (Δ) the product of the wavelength and the corresponding path length rather than the wavelength for each path or the path length. We also confirm our theoretical conclusion by numerical simulations. The result shows we must make a trade-off between resolution and visibility in devise practical experiments, as the resolution of the imaging can be improved by decreasing Δ but with visibility getting poor, and vice versa.     

四光路透镜成像系统研究

针对现有膜厚监控系统的双平行光路系统和监测光直接照射单色仪入射狭缝的结构，提出了四光路透镜成像系统，同时采用光纤传光。实验表明它提高了膜厚监的稳定性和精度，并有较高的性能价格比，此外从理论上对多光路透镜成像系统的设计和调校进行了定量分析。     

平面光栅双单色仪的光学系统设计

平面光栅双单色仪是构成光栅衍射效率测试仪的重要组成部分,为了完成光栅衍射效率测试仪的研制,需要对平面光栅双单色仪的光学系统进行设计和模拟。仪器主要由光源、前置单色仪、测量单色仪和探测器组成;结合仪器的实际使用需要,确定了光源、探测器和光路结构,根据仪器的设计要求,分别对前置单色仪和测量单色仪的光学系统进行设计和模拟,给出了各自光学系统的像面点列图和实际光线追迹数据。设计结果保证了仪器光学系统的测量准确性。     

The Double Monochromator Geometric Theory and Compensation of Aberrations

The light path function for the double monochromator is constructed, and the formulas of account of the members of its expanding in ascending power series adequate for the defocusing and the first order astigmatism aberrations are found. On the basis of results of the minimisation of obtained expressions the opportunity of construction of a double monochromator so that the second monochromator fractionally compensates aberrations of the first one is analysed. It is also noticed, that in the scheme of the double monochromator under certain conditions compensation of an astigmatism of the second order is automatically carried out. It allows to use a deviation angle of the scheme for more complete compensation of other aberrations and to develop double monochromators with the improved performances.This paper was originally presented at the 2nd International Conference on Optical Design and Fabrication, ODF2000 which was held on November 15-17, 2000 at the International Conference Center, Tokyo, Waseda University, Japan.     

大气信道简化单次散射模型

采用椭球坐标系研究非直视日盲紫外光通信的单次散射模型,求解过程中要对有效散射体的体积进行复杂的数值积分并确定三组积分限。为便于分析,使用近似表达式极大简化了复杂单次散射信道模型,得出路径损耗是收发机几何结构与大气散射吸收系数的函数。对传输距离和路径损耗的仿真证明,该近似表达式与原始模型的所得结果吻合很好。利用该近似表达式,分别仿真分析了大气能见度对紫外光通信系统路径损耗和误码率的影响,仿真结果表明,大气能见度并不是越高越好,而是在能见度为10 km时紫外光通信系统有最佳性能。     

大气信道简化单次散射模型

采用椭球坐标系研究非直视日盲紫外光通信的单次散射模型,求解过程中要对有效散射体的体积进行复杂的数值积分并确定三组积分限。为便于分析,使用近似表达式极大简化了复杂单次散射信道模型,得出路径损耗是收发机几何结构与大气散射吸收系数的函数。对传输距离和路径损耗的仿真证明,该近似表达式与原始模型的所得结果吻合很好。利用该近似表达式,分别仿真分析了大气能见度对紫外光通信系统路径损耗和误码率的影响,仿真结果表明,大气能见度并不是越高越好,而是在能见度为10 km时紫外光通信系统有最佳性能。     

全息凹面光栅单色仪

此种单色仪专配焦比约为F/3的全息凹面光栅。在机械结构简单的前提下,设计了一种新光路,使其聚焦精度尽可能地提高。设计的基本思想是在濑谷-布岗(Seya-Namioka)和Johnson装置的基础上另选转轴的位置,并选用两个标准波长来校正光谱,这类似于三点统调法。所得结果比濑谷-布岗装置和Johnson装置都有改善。按照这种设计装架了JS-II型凹面光栅单色仪。仪器可在波长为2500?至10000?范围内工作,在3500?至6500?范围内,由于聚焦偏离而引起的分辨率损失不超过1?。 关键词：     

Comprehensive experimental test of quantum erasure

In an interferometer, path information and interference visibility are incompatible quantities. Complete determination of the path will exclude any possibility of interference, rendering zero visibility. However, it is, under certain conditions, possible to trade the path information for improved (conditioned) visibility. This procedure is called quantum erasure. We have performed such experiments with polarization-entangled photon pairs. Using a partial polarizer, we could vary the degree of entanglement between the object and the probe. We could also vary the interferometer splitting ratio and thereby vary the a priori path predictability. This allowed us to test quantum erasure under a number of different experimental conditions. All experiments were in good agreement with theory. Received 15 July 2001 and Received in final form 30 November 2001     

Advantages of a monochromator for bandgap measurements using electron energy-loss spectroscopy

The practical advantages of a monochromator for electron energy-loss spectroscopy (EELS) in transmission electron microscopy are reviewed. The zero-loss peaks (ZLPs) of a monochromator and a cold field emission gun are compared in terms of bandgap measurement performance. The intensity of the ZLP tails at the bandgap energy is more important than the full-width at half maximum of the ZLP, and a monochromator is preferable to conventional electron sources. The silicon bandgap of 1.1eV is evaluated from the onset in the EEL spectrum obtained using the monochromator without a numerical procedure. We also show a high-speed instability-correction technique to realize the inherent energy resolution of the monochromator, in which instabilities of less than 335Hz are corrected using 512 EEL spectra obtained with an exposure time of 1.4ms. It will be useful in bandgap measurements and advanced studies for elucidating sub-eV EEL spectra.     

Characterization of the transverse coherence of hard synchrotron radiation by intensity interferometry

The transverse coherence of x rays was measured with an intensity interferometer using a 120-microeV-bandwidth monochromator operating at 14.41 keV. By analyzing the transverse coherence profiles, a vertical source profile of a 25-m long undulator of SPring-8, as well as the coherence degradation by a phase object in the beam path, were quantitatively characterized.     

Polarizer-Free Acousto-Optic Monochromators

Monochromators based on a noncollinear acousto-optic filter without external polarizers have been studied. As an element to select an operating diffracted light beam, (1) a spatial filter-telescope and (2) an output plane of a filter crystal rotated in a diffraction plane have been used. In the latter case, dispersion of the acousto-optic filter crystal is compensated using a correcting prism made from the same crystal and placed behind an output filter plane along a path of a filtered light beam. As a result, the transmission coefficient of the monochromator is increased upon an effective compensation of the angular drift of the filtered light beam, the monochromator design is simplified, and its sizes are decreased.

     

A new ray-tracing program RIGTRACE for X-ray optical systems

A new ray-tracing simulation program, RIGTRACE, has been developed specifically for the X-ray optics range. It traces consecutively each ray, following its path from the source to the observation plane, and treats diffraction by a monochromator crystal by adopting the Darwin-Prins theory so that it may be seen how rays of slightly different energies and incident angles reach the plane. It is also possible to treat the case of the laboratory system, in which the optical elements are disposed close to each other. Examples of the application are provided.     

The design and construction of a VUV Ar-arc source and a VUV monochromator

The design and construction of a VUV source and a VUV monochromator is reported. The reliability of the VUV source suggests that it can be used as a VUV high radiance transfer secondary standard. A VUV window is used to isolate the high pressure argon-arc source from the VUV monochromator. The spectrum is therefore limited by the transmission cut-off of the window. Alternatively, a differential pump could be used to extend the wavelength range to the extreme UV and eliminate the uncertainties associated with the aging effects of the VUV window. The apparatus is to be used to measure the VUV spectra of certain glass samples.We wish to acknowledge the financial support by SERC under research grant number GR/E 01973.     

Second-order temporal interference of two independent light beams at an asymmetrical beam splitter

The second-order temporal interference of classical and nonclassical light at an asymmetrical beam splitter is discussed based on two-photon interference in Feynman's path integral theory. The visibility of the second-order interference pattern is determined by the properties of the superposed light beams, the ratio between the intensities of these two light beams, and the reflectivity of the asymmetrical beam splitter. Some requirements about the asymmetrical beam splitter have to be satisfied in order to ensure that the visibility of the second-order interference pattern of nonclassical light beams exceeds the classical limit. The visibility of the second-order interference pattern of photons emitted by two independent single-photon sources is independent of the ratio between the intensities. These conclusions are important for the researches and applications in quantum optics and quantum information when an asymmetrical beam splitter is employed.     

软X射线谱学显微光束线单色器结构设计及精度测试

针对上海光源谱学显微光束线站的性能要求,对其核心部件单色器进行结构设计。阐述了单色器的扫描运动原理,论述了波长扫描机构的设计方案,具体分析平面镜和光栅的转角重复精度影响因素;描述光栅切换机构,着重分析其水平偏差、垂直偏差、滚角、摆角和投角的精度问题;采用六杆并联机构的方案完成镜箱调节机构的设计,分析其支杆的调节范围和分辨力情况。给出了单色器的结构,并且对其精度进行了测试。测试结果表明,平面镜和光栅的转角重复精度分别为0.166″和0.149″;光栅切换机构的滚角、摆角和投角的重复精度分别为0.08″、0.12″和0.05″。这说明了单色器的结构设计方案和机械精度满足技术要求。     

线性渐变滤光片光谱分光特性及检测方法研究

线性渐变滤光片(LVF)被广泛应用于各种小型快速分光测试设备中。分光特性进行研究,给出了其分光特性的高斯函数表达式,分析了各个参数与线性渐变滤光片中心透过率、谱线宽度和线性渐变系数等特性的关系。将光谱成像仪标定的单色仪法引入线性渐变滤光片的分光特性检测中,讨论了检测系统的敏感性,并给出了相应的误差容限公式。分析表明单色仪出射狭缝相对光轴平移量,以及滤光片倾斜角度对检测精度影响最大,实际测量中可通过光路和系统机构的调整达到精度要求。构建检测系统完成了对成品线性渐变滤光片分光特性的检测,结果表明对中心透过率的测量均方根误差小于0.05%,验证了方法的精确性,普适性,检测结果可为线性渐变滤光片相关系统的设计和标定提供参数指导。     

Laboratory vacuum spectrometer for the soft x‐ray region

A laboratory surface x‐ray absorption near edge structure ((S)XANES) spectrometer used for measurements in the soft x‐ray region is described. The x‐ray beam path of the spectrometer is enclosed in a vacuum chamber directly connected to the x‐ray generator output port. With this setup, the absorption of the x‐rays in the air is avoided. The developed spectrometer uses a monochromator equipped with cylindrically bent PET(002), KAP(001), and Ge(111) crystals of different Rowland radii working in the Johann focusing geometry. Nine stepping motors are used to control the positions of the monochromator, receiving slit, sample, and detectors. An x‐ray photon energy available in experiment ranges from about 1 keV to 5 keV. A registration of the photoelectrons emitted from the sample with the channeltron is used to carry out surface‐sensitive measurements. The performance of the developed spectrometer is illustrated by spectra measured at the absorption K‐edges of several elements from the Na‐Ti set. Copyright © 2008 John Wiley & Sons, Ltd.     

基于连续光谱光源的单色仪标定方法

单色仪在加工和安装过程中不可避免的存在误差,必须对其进行标定后才能使用。传统上采用汞灯的标定方法,波长数量有限,限制了单色仪的标定精度。在研究光栅单色仪原理的基础上,提出了一种基于连续光谱光源的单色仪标定方法,设计并搭建了标定实验系统,系统由宽波段光源、光源电源、滤光片、单色仪、光谱仪及计算机构成。采用卤钨灯作为光源,用光谱仪分别测量卤钨灯经单色仪后的辐射、直接测量卤钨灯的辐射,二者相比得到单色仪透过率函数,消除了卤钨灯辐射以及光谱仪响应函数的影响。在刻度盘的某一读数位置,获得单色仪透过率函数并进行归一化,并计算峰值波长,得到一组峰值波长和刻度盘读数的数据。该方法共采集了22组波长数据,用于单色仪的标定。分别采用8点、14点、18点、22点,采用线性拟合和二次拟合,得到了单色仪的波长与刻度盘读数的关系式。标定点数从8个(8点标定类似于汞灯特征谱标定)增加到22个,误差减小明显,将22点二次拟合的结果作为单色仪最终的标定结果。实验结果表明,采用连续光谱光源的单色仪标定方法获得的标定点数更多,标定结果优于传统的采用汞灯的标定方法。