四元数方法表示的反射和折射定律

在讨论四元数及其基本运算、Rodrigues-Hamilton参数表示的四元数和四元数变换算子的基础上,给出了标准四元数的定义。基于标准四元数,推导了四元数方法表示的光线反射和折射变换算子,并给出了对应的计算公式,为复杂光学系统以及失调光学系统的空间光线传输计算奠定了理论基础。     

广义折反射定律

折射和反射是波动传播时的基本现象,光波、电磁波和声波等均可被材料界面折射和反射。近来研究发现,通过在界面上制备人为设计的亚波长结构阵列,可改变传统折射和反射行为,为成像、电磁/几何外形解耦、全息显示等技术提供新的手段。本文综述了近年来折反射定律研究取得的进展,介绍了不同材料体系中波的折反射行为,阐述了相关的基本理论和具体应用。最后,结合本课题组的最新结果,分析了现有研究存在的不足,展望了本领域未来的发展趋势。

     

Transmission and reflection of Gaussian beams by anisotropic parallel plates

Explicit and compact expressions describing the reflection and the transmission of a Gaussian beam by anisotropic parallel plates are given. Multiple reflections inside the plate are taken into account as well as arbitrary optical axis orientation and angle of incidence.     

Effects of phase changes on reflection and their wavelength dependence in optical profilometry

The method as well as an appropriate instrumentation for measuring phase changes of reflected light is described. The phase changes on samples of Au, Al, Ag, and Cr evaporated films are measured for five wavelengths (lambda) from 442 to 633 nm, with respect to the phase change at the glass-air interface, where it should be zero. The measured results for the Au film are in fairly good agreement with values calculated by use of optical constants from a handbook or the complex refractive index measured by an ellipsometer. The phase changes for Al and Ag films are different from calculated values by ~5 degrees or a shift length of 4.4 nm at lambda = 633 nm, while those of the Cr film show large shifts as high as 16 degrees or a shift length of 9.8 nm at lambda = 442 nm.     

Efficient tunability and circuit model of nested-U nanoresonators in optical metasurfaces

Tunable metasurfaces can be employed to physically or mechanically engineer and control electromagnetic wave properties like reflection and transmission and their associated spectral characteristics like resonance frequency. Here, we propose highly tunable and sensitive metasurfaces composed of an array of a nested double U-shaped (NDU) nanoresonators on elastic polydimethylsiloxane substrate, operating in infrared region. The mechanical deformation varies the spaces between the coupled resonator elements which in turn leads to corresponding variations in the equivalent capacitance and inductance between the U-shaped elements causing efficient tunability. In addition to the higher signal strengths, it is also reported that the resonant frequency of the proposed metasurface exhibits substantial spectral shift. The observed remarkable trends are adequately verified by the developed equivalent circuit model for the proposed NDU-structure.     

Beam shaping with diffuse light by use of a single reflection

A technique for diffuse beam shaping is presented. The beam shaping is achieved by a single reflection on an element, which consists of many displaced parallel planar reflecting facets. The reflecting facets approximate a designed curved surface. We demonstrate the validity of the method for the conversion of a diffuse Gaussian beam into a uniform one in one of the spatial dimensions.     

全金属超表面在电磁波相位调控中的应用及进展

全金属超表面是由亚波长金属单元所组成的结构阵列,其在调控电磁波相位方面展现出了效率高、带宽大等特点,并且相较于金属-介质混合型超表面,全金属超表面具有优良的热学和机械性能,如耐高温、强度大、延展性好等,这使得其可以应用于高温高压等极端复杂环境中。本文对近年来全金属超表面取得的研究进展进行了简要的归纳总结,主要介绍了其在构建高效、多功能平面光学器件以及多频谱电磁隐身中的应用,并对其未来的发展方向进行了展望。

     

Acoustic reflection from the boundary of anisotropic thermoviscoelastic solid with fluid

Vertical slownesses of waves at a boundary of an anisotropic thermoviscoelastic medium are calculated as roots of a polynomial equation of degree eight. Out of the corresponding eight waves, the four, which travel towards the boundary are identified as upgoing waves. Remaining four waves travel away from the boundary and are termed as downgoing waves. Reflection and refraction of plane harmonic acoustic waves are studied at a plane boundary between anisotropic thermoviscoelastic solid and a non-viscous fluid. At this fluid-solid interface, an incident acoustic wave through the fluid reflects back as an attenuated acoustic wave and refracts as four attenuating waves into the anisotropic base. Slowness vectors of all the waves in two media differ only in vertical components. Complex values of vertical slowness define inhomogeneous refracted waves with a fixed direction of attenuation, i.e. perpendicular to the interface. Energy partition is calculated at the interface to find energy shares of reflected and refracted waves. A part of incident energy dissipates due to interaction among the attenuated refracted waves. Numerical examples are considered to study the variations in energy shares with the direction of incident wave. For each incidence, the conservation of incident energy is verified in the presence of interaction energy. Energy partition at the interface seems to be changing very slightly with the azimuthal variations of the incident direction. Effects of anisotropy, elastic relaxation and thermal parameters on the variations in energy partition are discussed. The acoustic wave reflected from isothermal interface is much significant for incidence around some critical directions, which are analogous to the critical angles in a non-dissipative medium. The changes in thermal relaxation times and uniform temperature of the thermoviscoelastic medium do not show any significant effect on the reflected energy.     

Reflection and refraction of light at saturating active boundaries

Abstract

This study deals with the topic of reflection and refraction of light from the boundary of a high-gain saturating laser amplifier. Expressions for the electric field and intensity reflection and transmission coefficients are obtained for the case of a wave in a uniform dielectric that is incident normally on a nonlinear saturating active medium. Bistability effects are predicted even for the simplest case of zero frequency detuning from the line centre of the saturating transition.     

Polarization-based index of refraction and reflection angle estimation for remote sensing applications

A passive-polarization-based imaging system records the polarization state of light reflected by objects that are illuminated with an unpolarized and generally uncontrolled source. Such systems can be useful in many remote sensing applications including target detection, object segmentation, and material classification. We present a method to jointly estimate the complex index of refraction and the reflection angle (reflected zenith angle) of a target from multiple measurements collected by a passive polarimeter. An expression for the degree of polarization is derived from the microfacet polarimetric bidirectional reflectance model for the case of scattering in the plane of incidence. Using this expression, we develop a nonlinear least-squares estimation algorithm for extracting an apparent index of refraction and the reflection angle from a set of polarization measurements collected from multiple source positions. Computer simulation results show that the estimation accuracy generally improves with an increasing number of source position measurements. Laboratory results indicate that the proposed method is effective for recovering the reflection angle and that the estimated index of refraction provides a feature vector that is robust to the reflection angle.     

Splitting light beam by meanderline with continuous phase profile

It has been successfully demonstrated can be widely used in nano-photonics applications owing to their flexible wavefront manipulation in a limited physical profile. However, how to improve the efficiency for the transmission light is still a challenge. We experimentally demonstrate that the sine-shaped metallic meanderline fabricated by focus ion beam technology converts circularly polarized (CP) light to its opposite handedness and sends them into different propagation directions depending on the polarization states in near-infrared and visible frequency regions. The beam splitting behavior is well characterized by a simple geometry relation, following the rule concluded from other works on the wavefront manipulation of metasurface with phase discontinuity. Importantly, the meanderline is demonstrated to be more efficient in realizing the same functions due to the suppressed high order diffractions resulted from the absence of interruption in phase profile. The theoretical efficiency reaches 67%. Particularly, potential improvements are feasible by changing or optimizing shape of the meanderline, offering high flexibility in applications for optical imaging, communications and other phase-relative techniques. Additionally, since the continuous phase provided by the meanderline can improve the sampling efficiency of the phase function, it is helpful in realizing high quality hologram.     

光反射干涉谱新方法测试薄膜厚度和光学常数

依据测量薄膜和光之间相互作用可确定薄膜特性的原理,并基于光反射干涉谱与德国最新研发薄膜分析软件SCOUT的新方法可测量已知或未知材料的多层薄膜厚度及其折射率n、消光系数k。通过实际测试证明：该方法可测试单晶硅、玻璃、ITO玻璃基底上沉积薄膜的厚度,样品基本不需要特别准备,对样品无破坏性,测试精准。理论上可以测量所有透光或半透光薄膜的厚度和光学常数,操作非常简便,适合于镀膜行业的在线检测和实时监控,且SCOUT软件在多层膜及多种材料的研发、制备等方面具有应用潜力。     

Straightness measurements by use of a reflection confocal optical system

Straightness measurement is a very important technique in the field of mechanical engineering. A particular application for straightness measurement is high-accuracy machining on a diamond-turning lathe. We propose a novel, to our knowledge, optical method for measuring the straightness of motion, and its mathematical analysis is outlined. The technique is based on measurement of the lateral displacement of point images by use of reflection confocal optical systems. The advantages of this method are that (i) the lateral displacements in the direction of the two axes perpendicular to the optical axis can be measured, (ii) the rotation angles around all three axes can be measured, and (iii) reflection optical systems are more compact in length than are transmission optical systems.     

Implementation of high-resolution diffractive optical elements on coupled phase and amplitude spatial light modulators

We propose the optical implementation of diffractive optical elements onto electrically addressed liquid-crystal spatial light modulators. We compare the classic implementations onto amplitude-only or phase-only domains with the implementations onto coupled phase and amplitude (spiral) domains. We demonstrate that the coupling between amplitude and phase provides a trade-off between diffraction efficiency and the signal-to-noise ratio in the reconstruction. Furthermore, when investigating the influence of the maximum dephasing on phase domains and spiral domains through the use of optimal trade-off design, we show that phase-only domains with limited maximum dephasing can provide satisfactory performance. Finally, optical implementations are provided.     

Short optical pulse refraction by a thin film of atoms at two-photon resonance

Abstract

The refraction of a short pulse by a thin film of atoms at two-photon resonance is numerically considered with the process of third harmonic generation involved in the analysis. It is shown that a light pulse, being refracted by a thin film of resonance atoms, decays into subpulses, whose number is determined by the energy penetrating the film. The process depends on the angle of incidence. The variation on the resonance detuning allows compensation of the Stark effect and creation of preferable conditions for light pulse transmission. The effect of local field is similar in its action to the Stark effect, but its contribution to the frequency shift could be significant only in media with a greater concentration of the resonance atoms.     

Intensity and phase mapping of guided light in LiNbO3 waveguides with an interferometric near-field scanning optical microscope

The design and implementation of a phase-sensitive near-field scanning optical microscope incorporating both heterodyne interferometric detection and a phase feedback mechanism are described. Using this microscope we demonstrate a new method for measuring the effective index of the guided mode of a waveguide from the phase images. Two types of LiNbO3 waveguide, defined by titanium diffusion or annealed proton exchange, were studied. Both the profile and the effective index of the mode were measured experimentally. For titanium-diffused waveguides, both agree well with values determined from numerical simulation. In annealed proton-exchanged waveguides that contain periodically poled domains, we find evidence for backreflection from the boundaries between neighboring regions of opposite pole directions, which could result in transmission loss in this type of waveguide.     

Anomalous behaviour of light reflection in crystals with different homogeneity

The light reflection as a function of the sample length has been studied for an ideal two-dimensional photonic crystal and for a two-dimensional photonic structure with smaller homogeneity with respect to the photonic crystal. We have found that, although the number of the scattering elements is constant for the two structures, the behaviour of the light reflection increases linearly with the sample length in the less homogeneous photonic structure, while it is strongly sub-linear in the photonic crystals.