Nanostructured gradient-index antireflection diffractive optics

We describe the fabrication and characterization of a nanostructured diffractive element with near-zero reflection losses. In this element, subwavelength nanostructures emulating adiabatic index matching are integrated on the surface of a diffractive microstructure to suppress reflected diffraction orders. The fabricated silicon grating exhibits reflected efficiencies that are suppressed by 2 orders of magnitude over broad wavelength bands and wide incident angles. Theoretical models of the fabricated structure based on rigorous coupled-wave analysis and effective medium theory are in agreement with the experimental data. The proposed principles can be applied to improve the performance of any diffractive structures, potentially leading to more efficient Fresnel lenses, holographic elements, and integrated optical systems.     

Rydberg molecules in external fields: a semiclassical analysis

We analyze the spectra of simple Rydberg molecules in static fields within the framework of closed/periodic-orbit theories. We conclude that in addition to the usual classical orbits one must consider classically forbidden diffractive paths. Further, the molecule brings in a new type of "inelastic" diffractive trajectory in addition to the usual "elastic" diffractive orbits encountered in systems with point scatterers. The relative importance of inelastic versus elastic diffraction is quantified by merging the usual closed orbit theory framework with molecular quantum defect theory.     

Optical Characterization of Iridescent Wings of <Emphasis Type="Italic">Morpho</Emphasis> Butterflies using a High Accuracy Nonstandard Finite-Difference Time-Domain Algorithm

In certain species of moths and butterflies iridescent colors arise from subwavelength diffractive surface corrugation of the wing-scales. The optical properties of such structures depend strongly on wavelength, incidence angle, and state of polarization of illuminating radiation, and the viewing angle. In this paper, we study the reflection spectra of the wings of the Morpho didius butterfly by simulating a double-layered model of a transverse cross-section comprised of the ground scale and the cover scale. Each layer contains a certain quasi-periodic arrangement of tree-like subwavelength microstructures. The simulation is done using a high accuracy nonstandard finite-difference time-domain (FDTD) method in two dimensions. We assume that the structure is made of a slightly lossy dielectric material. The wavelength dependence of the complex refractive index for the ground scale of Morpho didius is assumed to be similar to that of Morpho sulkowskyi. The complex refractive index in the latter case was obtained by comparing the computed reflection/transmission spectra with corresponding experimental measurements at normal incidence.     

位相光栅的衍射级次

用矢量衍射理认讨论了位相光栅衍射级次的有限性及其与入射角的关系，得出的吉论与用光程方法得出的结果一致，作出了在不同入射角条件下各衍射级次的分布图，给出了求解各级衍射波方向的公式。     

高散射媒质中的光程可分割动态光散射研究

为研究散射光强度随光子在散射媒质中散射光程的变化,基于单散射理论与扩散波光谱理论,采用了低相干动态光散射装置对不同粒径大小的聚苯乙烯悬浮液进行研究。将测量得到的背散射光光场强度谱的线宽与相应的理论计算结果相比较发现,在短光程区域,考虑容器壁附近拖曳效应的影响后,对于不同粒径的颗粒,光程为约5倍粒子平均自由程的区域可看成为单散射区域;对于光程大于225 m的区域可看成为扩散光波区域。实验结果表明低相干动态光散射法可实现高散射媒质从单散射区域到低次散射再到扩散区域的全光程的可分割的光场强度谱测量。     

Studying Diffractive Orders of the Phase Grating

Abstract

The finiteness of diffractive orders of the phase grating and the relations between the diffractive orders and the incident angle are discussed in this article. The distribution of each diffractive order is illustrated at different incident angles, and the diffractive direction of each diffraction wave is given. It is pointed out that while only the zero-order reflection wave and the zero-order transmit exist in the free-space layer, the diffraction waves of higher diffractive orders may exist in the substrate layer.     

Focusing light with a reflection photon sieve

An advanced type of diffractive optical element is presented that combines the concept of the photon sieve with an off-axis, off-normal incidence reflection geometry. Compared to transmission optical elements, the signal-to-background ratio is significantly increased by separating the first from other diffraction orders without drastically reducing the size of the smallest diffractive element. The reflection photon sieve produces sharp foci at maximum contrast and offers the advantages of effective heat dissipation and a large working space above the focal plane. Experimental results for a device working at a photon energy of 100 eV are presented and compared to theory.     

大口径折反式中波红外衍射望远镜系统设计

为实现空间红外望远镜的高分辨率探测,基于Schupmann消色差理论,开展了大口径折反式中波红外衍射望远镜系统的设计及消热差模型研究.设计了口径1 m、F数为2、全视场0.12°、波段3.8μm～4.2μm的折反式中波红外衍射望远镜系统,其主镜及校正镜均为平面衍射透镜,中继系统采用卡塞格林折反式结构,再聚焦及三次成像系...     

利用傅里叶模方法分析厚层光刻胶内衍射光场

建立了描述厚层光刻胶内衍射光场形成过程的物理模型,并利用傅里叶模方法模拟计算和分析了其内部衍射光场分布。该方法考虑了其界面反射、透射及光刻胶复折射率在空间上的缓慢变化对衍射光场的影响,采用该方法模拟光刻胶内衍射光场具有数值计算结果准确、计算速度快的优点。对厚层光刻胶折射率在几种特殊分布情况下衍射光场分布的数值模拟表明,衍射光场与其复折射率的空间分布有关。由于厚层光刻胶折射率在空间上呈缓慢变化的特点,为降低其数值计算量和编程难度,可以将厚层光刻胶近似为折射率随曝光时间变化的光栅。     

Optical properties of a stack of layers of a cholesteric liquid crystal and an isotropic medium

Optical properties of a stack consisting of layers of a cholesteric liquid crystal (CLC) and an isotropic medium are investigated. The problem is solved using the modified Ambartsumyan layer-summation method. Particular features of reflectance spectra of this system are studied. It is shown that, in contrast to a single CLC layer, this system exhibits multiple photonic band gaps. There are two types of photonic band gaps: selective and nonselective with respect to polarization of the incident light. It is shown that eigenpolarizations in the system generally coincide with quasi-orthogonal quasi-circular polarizations, except for regions that are selective with respect to polarization of the diffractive reflection. It is shown that, for an even number of layers, the system under consideration is nonreciprocal and can function as an optical diode. The influence of thickness of CLC sublayers, angle of incidence, local dielectric anisotropy of CLC layers, refractive indices and thicknesses of layers of an isotropic media on reflectance spectra and other optical characteristics of the system is investigated.     

一种普适型国产银盐感光胶的全息特性实验研究

实验研究了一种普适型国产HR_1型卤化银乳胶的主要全息特性;论述了其曝光量对衍射效率的影响;比较了两种化学后处理方法对衍射效率和信噪比的影响。实验结果表明,HR_1型卤化银乳胶是一种适合于记录透射和反射型合成全息图的记录介质,可以获得较高的衍射效率和信噪比。     

人膀胱粘膜/粘膜下层组织病变致组织漫反射光谱的变化

研究了人正常膀胱和浅表性膀胱癌的粘膜/粘膜下层组织在300～900nm光谱范围的漫反射光谱特性及其差异,实验采用带积分球附件的分光光度计获取组织的漫反射光谱.结果表明,在300～900 nm,正常膀胱的粘膜/粘膜下层对任一个波长的漫反射率都明显地较癌变的粘膜/粘膜下层对相应波长的要大.正常膀胱的粘膜/粘膜下层的漫反射光谱的峰分别在370 nm、520 nm、550 nm和660nm,其峰值分别为52.4%、60.7%、56.1%和75.5%.而癌变的粘膜/粘膜下层的漫反射光谱的峰分别在320 nm、520 nm、550 nm和660 nm,其峰值分别为43.7%、33.4%、30.6%和70.2%.正常膀胱的粘膜/粘膜下层的漫反射光谱在370 nm处有一个峰,而癌变的粘膜/粘膜下层的漫反射光谱在370 nm处没有峰,320 nm处有一个峰.而正常膀胱的粘膜/粘膜下层的漫反射光谱在320 nm处没有峰.膀胱的粘膜/粘膜下层病变导致组织的漫反射光谱在520 nm、550 nm和660 nm处的峰的峰值分别减小了45.0%、45.5%和7.02%.说明膀胱的粘膜/粘膜下层病变导致组织的组分和结构尤其足组织中的氧合血红蛋白和去氧血红蛋白的含量发生了明显的改变.     

中红外无创血糖测量中光程变化对PLSR模型的影响研究

在测量人体皮肤中红外光谱的过程中,皮肤与ATR晶体之间的接触面积很难保持一致,导致倏逝波与人体皮肤的作用光程会产生差异。以光程变化信息与葡萄糖浓度信息之间的相关性为基础,建立了两个分析葡萄糖含量的偏最小二乘回归(PLSR)模型,RMSECV分别为31.3和4.52mg.dL-1;RMSEP分别为30.3和98.7mg.dL-1。结果表明,当光程变化信息与葡萄糖浓度信息之间偶然相关时,所建PLSR模型的预测精度与稳健性会受到不同程度的影响,随着二者之间相关性的增强,最优模型对葡萄糖信息的识别能力越来越弱。为提高中红外无创血糖测量分析结果的可靠性,避免获得伪优定标模型提供了实验依据。     

Surface‐sensitive reflection‐mode EXAFS from layered sample systems: the influence of surface and interface roughness

The calculation of reflection‐mode grazing‐incidence X‐ray absorption spectra from single surfaces and (multi‐)layered systems is studied here. In particular, the influence of the surface and interface roughness was investigated in detail. Simulations of grazing‐incidence reflection‐mode EXAFS spectra using a simple Fresnel theory neglecting any effect of roughness are compared with the Névot–Croce model and the elaborated distorted‐wave Born approximation which both include surface and interface roughness. Data are presented for clean gold surfaces, where the strong influence of the surface roughness on the resulting spectra is demonstrated. Furthermore, in the case of layered systems, the influence of both the outer (air or vacuum side) surface roughness and the inner interface roughness on the reflection‐mode EXAFS spectra is evaluated. The practical consequences of the observed correlations are discussed, and a quantitative data analysis of a copper sample that was oxidized in ambient air for several months is shown, including the evaluation of specular reflectivity profiles at fixed energy.     

折-衍混合超广角视场目镜系统的设计

在传统的超广角 (70°)赛得莫尔 (Scidmore)目镜的基础上 ,设计了两个折衍混合 70°视场的目镜。其中一个混合系统含有两个折衍单透镜 ,另一个含有一个折衍单透镜。所设计的混合系统与赛得莫尔目镜进行了像差和结构的比较 ,表明折衍混合目镜系统不仅在诸如垂轴像差、垂轴色差、平均场曲等光学性能方面优于传统的赛得莫尔目镜系统 ,而且在尺寸和重量上有非常显著的减少。最后讨论了衍射面的结构参量。     

FAR-INFRARED AND INFRARED REFLECTIONS OF Tl2Ba2Ca2Cu3O10 FILM

The far-infrared and infrared reflection spectra of Tl₂Ba₂Ca₂Cu₃O₁₀ superconducting film are reported in this paper. It is found there are three sharp reflection edges in both the superconducting and normal states, their positions being near ≈ 150, ≈ 350 and ≈600 cm^-1. We attribute these reflection spectra to the Drude free carriers and a wide mid-infrared absorption band. When the incident angle increases from 7° to 30°, some additional stractures appear in the refiection spectra, which are the A_2u phonon modes vibrating along c-axis.     

折/衍混合单透镜在目镜中的应用研究

以传统凯涅尔目镜为基础，采用ZEMAX软件，设计了衍射面位于目镜系统中不同位置时的折／衍混合目镜系统，所有系统均仅采用最普遍的K9玻璃，设计结果与传统凯涅尔目镜的光学性能进行了分析和比较。结果表明折／衍混合目镜系统在校正目镜的像差，例如像散，垂轴色差、垂轴像差，轴向像差和轴向色差等方面优于传统的凯涅尔目镜，选择合适的衍射面位置，可以同时获得符合要求的畸变，衍射面的引入，极大地减小了系统的重量和尺寸。     

Correction of atmospheric scattering effects in space-based observations of carbon dioxide: Model study of desert dust aerosol

We describe an original methodology for CO₂ retrievals using space-based measurements of reflected sunlight spectra. The effects of optical-path modification by aerosols were considered in terms of photon path-length statistics. First, the general approach was verified using a representative set of photon trajectories produced by the Monte Carlo technique. This method enabled accurate consideration of optical-path modification by aerosols and was effective in CO₂ retrievals if aerosol optical properties were assumed. The next approach involved a limited number of parameters that describe the photon path-length distribution function (PPDF) and which were retrieved simultaneously with the CO₂ amount. This approach was efficient under conditions of strong path modification by desert dust aerosol. The retrieval procedure included the following: estimation of PPDF parameters from radiance spectra in the O₂ A-band; the necessary correction to use these estimated parameters in the 1.6-μm band; and, finally, CO₂ retrievals from the 1.6-μm band. The procedure was verified by numerical simulations using an independent radiative transfer approach to produce radiance spectra expected for the Greenhouse Gases Observing Satellite (GOSAT) sensor.     

Zone structure and polarization properties of the stack of a metamaterial-based cholesteric liquid crystal and isotropic medium layers

The optical properties of a stack of metamaterial-based cholesteric liquid crystal (CLC) layers and isotropic medium layers are investigated. The problem is solved by a modification of Ambartsumian’s layer addition method. CLCs with two types of chiral nihility are defined. The peculiarities of the reflection spectra of this system are investigated and it is shown that the reflection spectra of the stacks of CLC layers of these two types differ from each other. Besides, in contrast to the single CLC layer case, these systems have multiple photonic band gaps. There are two types of such gaps: those selective with respect to polarization of the incident light and nonselective ones. It is shown that the system eigenpolarizations mainly coincide with the quasi-orthogonal, quasi-circular polarizations for normally incident light, except the regions of diffraction reflection selective with respect to the polarization of incident light. The influence of the CLC sublayer thick-nesses, the incidence angle, the local dielectric (magnetic) anisotropy of the CLC layers, and the refractive indices and thicknesses of the isotropic media layers on the reflection spectra and other optical characteristics of the system is investigated.