Application of multilayer structures at millimeter wavelengths

The paper presents results of theoretical analyses and experimental investigations of the optical characteristics of devices based on multilayer dielectric structures and intended for the millimeter wave band. As is shown, multilayer dielectric structures can prove useful in devices with variable optical characteristics representing coupling elements for quasioptical open resonators, adjustable reflection coefficient mirrors in narrow-band interference Fabry-Perot filters or adjustable multilayer polarizers.     

基于偏振阵列的偏振迈克耳孙风场探测干涉仪系统的理论研究

基于偏振阵列的偏振迈克耳孙风场探测干涉仪是一种新型的探测大气温度和风场速度的干涉仪.基于偏振干涉的原理,四个偏振方向分别相差45°的偏振片组成的偏振阵列紧贴于探测器前,由四面角锥棱镜出射的四束线偏振光分别经四个不同偏振方向的偏振片后,四个不同强度干涉图同时成像于探测器上,经过数据提取获得四个干涉强度值,进一步反演出大气温度和风场速度值.对以上干涉成像过程进行了模拟仿真,得到干涉图,经风速反演得到了与实际值一致的结果.具有结构简单稳定,测试精度高,利于快速变化的目标测试的优点.     

Compound polarized wavelength filters with a single subwavelength structure

A novel dual functional device that combines functions of polarizing and bandpass filtering together using a single subwavelength structure is proposed. Characteristics of both wavelength filtering and polarizing in the visible wavelength range with two different multi-layer subwavelength structures are investigated. It is found that both filtering and polarizing functions can be realized simultaneously by appropriate design of the substrate, a dielectric layer and a metallic layer system. Dependence of tunable filtering central wavelength on the properties of layered materials and structural dimensions are discussed in detail. Typical optimized multilayer structural parameters are obtained, in which ~ 75% passband transmission with > 30 dB polarization extinction ratio have been achieved simultaneously for three primary color (red, green and blue) filters. The results open new possibilities in designing and fabricating novel multi-functional polarizing and filtering photonic devices using a single subwavelength structure.     

Instrumentation with polarized neutrons

Neutron scattering with polarization analysis is an indispensable tool for the investigation of novel materials exhibiting electronic, magnetic, and orbital degrees of freedom. In addition, polarized neutrons are necessary for neutron spin precession techniques that path the way to obtain extremely high resolution in space and time. Last but not least, polarized neutrons are being used for fundamental studies as well as very recently for neutron imaging. Many years ago, neutron beam lines were simply adapted for polarized beam applications by adding polarizing elements leading usually to unacceptable losses in neutron intensity. Recently, an increasing number of beam lines are designed such that an optimum use of polarized neutrons is facilitated. In addition, marked progress has been obtained in the technology of ³He polarizers and the reflectivity of large-m supermirrors. Therefore, if properly designed, only factors of approximately 2–3 in neutron intensity are lost. It is shown that S-benders provide neutron beams with an almost wavelength independent polarization. Using twin cavities, polarized beams with a homogeneous phase space and P>0.99 can be produced without significantly sacrificing intensity. It is argued that elliptic guides, which are coated with large m polarizing supermirrors, provide the highest flux.     

Linear optical implementation of optimal unambiguous discrimination among quantum states

In this paper, we present a linear optical scheme for optimal unambiguous discrimination among nonorthogonal quantum states in terms of the multiple-rail and polarization representation of a single photon. In our scheme, discriminated quantum states are expressed by using the spatial degree of freedom of a single photon while the polarization degree of freedom of the single photon is used to act as an auxiliary qubit. The optical components used in our scheme are only passive linear optical elements such as polarizing beam splitters, wave plates, polarizers, single photon detectors, and single photon source.     

基于评价函数的极紫外多层膜反射式起偏器和检偏器设计

 基于三种不同评价函数,利用全局优化算法设计了极紫外波段高性能反射式多层膜偏振元件。通过比对不同评价函数的设计结果,分析了评价函数、工作角度及膜层数对反射式多层膜偏振片性能的影响,确定了极紫外多层膜反射式偏振片设计的角度选择、膜层数选择及评价函数选择标准。为解决传统的单一性能优化造成的偏振度损失的问题,构造了偏振比对数结合反射率的评价函数,该方法设计的偏振元件性能优于传统优化方法设计的结果。     

液晶光阀大屏幕显示中的偏振分色系统

在液晶光阀全彩色大屏幕显示中，偏发色系统是极其关键的，它含偏振和分色两重功能于一体，直接对显示图像的亮度、对比及色平衡等指标作出贡献。本系统共有４个偏振或消偏振分光镜和红、绿、兰三个修饰滤光片组成，全部偏振分色滤光片被封在一个油箱内。该系统得到了很好的性能，具有很高的消光比。     

Optical clock distribution using integrated free-space optics

The design and experimental results of an optical clock distribution system based on integrated free-space micro-optics are reported. Planar optical components such as lenses, beamsplitters, and mirrors, are monolithically integrated on a single glass substrate to provide a stable and compact system. A single input beam is split and distributed evenly to N output positions using a binary tree of beamsplitters. The experiment shown demonstrates the principle idea for a system with a fanout of eight. Theoretical considerations show that a fanout of 64 or larger is feasible.     

Geometric phase and Pancharatnam phase induced by light wave polarization

We use the quantum kinematic approach to revisit geometric phases associated with polarizing processes of a monochromatic light wave. We give the expressions of geometric phases for any, unitary or non-unitary, cyclic or non-cyclic transformations of the light wave state. Contrarily to the usually considered case of absorbing polarizers, we found that a light wave passing through a polarizer may acquire in general a nonzero geometric phase. This geometric phase exists despite the fact that initial and final polarization states are in phase according to the Pancharatnam criterion and cannot be measured using interferometric superposition. Consequently, there is a difference between the Pancharatnam phase and the complete geometric phase acquired by a light wave passing through a polarizer. We illustrate our work with the particular example of total reflection based polarizers.     

Amplitude and phase characteristic of x-ray mirrors

The effect of absorption, interlayer roughness, and fluctuations of the layer thicknesses on the phase-shifting and polarization properties of multilayer structures has been investigated on the basis of coupled-mode equations. The conditions for the parameters of multilayer structures that make it possible to achieve the best phase-shifting characteristics of mirrors are formulated.     

Polarization measurements of laboratory VUV light: a first comparison between multilayer polarizers and photoelectron angular distributions

The use of photoelectron angular distributions to determine the linear polarization of VUV light over a wide range of photon energies is demonstrated. Light at wavelengths from 256 to 736 Å, partially polarized by large angle reflections in a toroidal grating monochromator and at a refocus mirror, has been analyzed. The results are validated by comparison measurements at spot wavelengths using multilayer polarizers.     

Sensitive and accurate dual-wavelength UV-VIS polarization detector for optical remote sensing of tropospheric aerosols

An UV-VIS polarization lidar has been designed and specified for monitoring aerosols in the troposphere, showing the ability to precisely address low particle depolarization ratios, in the range of a few percent. Non-spherical particle backscattering coefficients as low as 5×10^?8 m^?1?sr^?1 have been measured and the particle depolarization ratio detection limit is 0.6 %. This achievement is based on a well-designed detector with laser-specified optical components (polarizers, dichroic beamsplitters) summarized in a synthetic detector transfer matrix. Hence, systematic biases are drastically minimized. The detector matrix being diagonal, robust polarization calibration has been achieved under real atmospheric conditions. This UV-VIS polarization detector measures particle depolarization ratios over two orders of magnitude, from 0.6 up to 40 %, which is new, especially in the UV where molecular scattering is strong. Hence, a calibrated UV-VIS polarization-resolved time-altitude map is proposed for urban and free tropospheric aerosols up to altitude of 4 kilometers, which is also new. These sensitive and accurate UV-VIS polarization-resolved measurements enhance the spatial and time evolution of non-spherical tropospheric particles, even in urban polluted areas. This study shows the capability of polarization-resolved laser UV-VIS spectroscopy to specifically address the light backscattering by spherical and non-spherical tropospheric aerosols.     

Linear polarizer made of indefinite media

We propose a new type of polarizer that utilizes indefinite media–media for which not all elements of the permittivity and permeability tensors possess the same sign [5]. We demonstrate both theoretically and numerically that, when certain physical parameters are chosen, a slab of indefinite media can transmit all the p-polarized components of the incident electromagnetic waves and fully reflect the s-polarized ones; thus, it can be used as a linear polarizer or a polarizing beam splitter. The proposed polarizer has some advantages compared to polarizers of the conventional types. Practical models for such polarizers are also presented. PACS 42.79.Ci; 42.25.Gy; 78.67.-n     

Depth-enhanced integral imaging by use of optical path control

The image depth of integral imaging is enhanced by doubling the number of central depth planes by use of optical path control. To accomplish this, the optical path lengths are changed by controlling whether reflections occur behind the lens array. We propose three schemes that use mirrors, a combination of beam splitters and polarizers, and polarization beam splitters, respectively. In experiments we implement the systems that are completely electronically controllable, are compact, and provide two central depth planes with 50.4-mm separation.     

Nonlinear continual growth model of nonuniformly scaled reliefs as applied to the rigorous analysis of the X-ray scattering intensity of multilayer mirrors and gratings

It is revealed that certain terms entering into the nonlinear continual equation describing thin-film growth enable its application to the simulation of the surfaces of multilayer mirrors and gratings with a large height and/or jumps of boundary-profile gradients. The proposed model characterizes both variations in the power spectral-density function of the surface of Al/Zr multilayer mirrors and the smoothing and shift of the boundaries of Mo/Si and Al/Zr gratings grown on Si substrates with triangular groove profiles by means of magnetron and ion-beam deposition. Rigorous calculations indicate that the intensities of diffuse X-ray scattering by Au mirrors, which have similar boundary profiles with Gaussian and exponential autocorrelation functions, differ substantially from each other. Computer simulation of the growth of Mo/Si and Al/Zr multilayer gratings is performed. On the basis of the calculated boundary profiles, the absolute diffraction efficiencies of the Mo/Si and Al/Zr gratings are found via the integral equation method in the extreme UV region. It is demonstrated that the proposed comprehensive approach to calculations of the boundary profiles and the intensities of short-wavelength scattering from multilayer mirrors and gratings makes it possible to carry out studies comparable in accuracy to measurements based on synchrotron radiation.     

Design and performance of two-channel EUV multilayer mirrors with enhanced spectral selectivity

In this paper, we present a study on two-channel multilayer mirrors which can operate at two wavelengths in Extreme Ultraviolet (EUV) spectral range. We propose a new method to design two-channel EUV multilayer mirrors with enhanced spectral selectivity. The mirror structure is a stack of two periodic multilayers separated by a buffer layer. We have defined the main parameters which allow adjustment of the distance between different order Bragg’s peak and of wavelength positions of reflectivity minima. Two mirrors have been designed and deposited for solar EUV telescope applications by using this method. The first mirror reflects Fe IX–X line (17.1 nm) and Fe XVI (33.5 nm) lines with attenuation of the He II line (30.4 nm). The second mirror reflects Fe IX–X and He II lines with attenuation of Fe XV (28.4 nm) and Fe XVI lines. Measurements with synchrotron radiation source confirm that, in both cases, for these mirrors, we are able to adjust reflectivity maxima (Bragg peak position) and minima. Such multilayers offer new possibilities for compact design of multi-wavelength EUV telescopes and/or for high spectral selectivity.     

Influence of polarization and material on Brownian thermal noise of binary grating reflectors

Grating reflectors are a potential low-noise replacement for amorphous multilayer mirrors. We investigate the influence of polarization and refractive index on Brownian thermal noise of binary grating reflectors using Maxwell's stress tensor. Our results demonstrate that the refractive index of the grating material is a critical parameter for thermal noise in these structures. In contrast to multilayer mirrors, a low coating thickness does not necessarily lead to a low thermal noise amplitude for structures with low refractive index. We find that an improved noise performance of grating reflectors requires materials of refractive index ?2.5. We present a factorized expression for the thermal noise of grating reflectors made of arbitrary materials by simply scaling the noise amplitude with the related material parameters.     

Co/C and W/Si multilayers deposited by ion-beam sputtering for the soft X-ray range

We deposited Co/C multilayer mirrors for a wavelength of 4.77 nm and W/Si multilayer mirrors for a wavelength of 1.77 nm by use of ion-beam sputtering. The small-angle diffraction spectrum was used to analyze the structure of the multilayers. With a combination of the experimental diffraction spectra and Apeles’ theory for calculation of the interfacial roughnesses of the multilayers, the interfacial roughnesses of Co/C and W/Si are 0.80 nm and 0.60 nm, respectively, which are lower than that of the substrate. The reflectivity of the Co/C multilayer is measured to be about 20% and that of the W/Si multilayer about 1% at the grazing incidence angle of about 12°. Received: 30 May 2000 / Accepted: 1 August 2000 / Published online: 11 February 2002     

Improving attosecond pulse reflection by large angle incidence for periodic multilayer mirror in the extreme ultraviolet region

The improvement of attosecond pulse reflection by large angle incidence for periodic multilayer mirror in the extreme ultraviolet region has been discussed. Numerical simulations of both spectral and temporal reflection characteristics of periodic multilayer mirrors under various incident angles have been analyzed and compared. It was found that the periodic multilayer mirror under larger incidence angle can provide not only higher integrated reflectivity but also broader reflection band with negligible dispersion, making it possible to obtain better reflected pulse that owns higher pulse reflection efficiency and shorter pulse duration for attosecond pulse reflection. In addition, with increasing of incident angle, the promoting of attosecond pulse reflection capability has been proven for periodic multilayer mirrors with arbitrary layers.     

Design of transverse magnetic-reflected polarizing film

We propose a wideband transverse magnetic-reflected polarizing film composed of Cr and SiO2. Based on the polarization characteristics of reflected light from Cr/SiO2 film, the film can serves as a polarizer to severely attenuate the transverse electric （TE）-polarized light and reflect the transverse magnetic （TM）- polarized light in a wavelength range from 600 to 900 nm. By suitably choosing the film thicknesses, the operation angles of such polarizers can be adjusted over a wide angle range greater than the critical angle of total reflection. Cr/SiO2 film has potential use in surface plasmon resonance （SPR） sensors based on Kretchmann configuration to form integrated structures.