Fraunhofer diffraction of a slit aperture between a knife-edge and a metal cylinder

The Fraunhofer diffraction pattern of a slit aperture formed between a reference knife-edge and a metal-cylinder surface is different from that of an ideal slit aperture. This pattern should include reflected light coming from both the front and rear sides of a cylinder surface. To investigate the influence of light reflected from the cylinder surface, we discuss the theoretical consideration based on the simple model of the reflected light on the surface. The experimental setup is designed and constructed to measure the actual diffraction pattern produced by the slit between the knife-edge and the cylinder surface. As a result it is obvious that the reflection of diffracted light on the rear side is dominant in both the simulation and the experiment.     

Interference of Acoustically Phase-modulated Light Transmitted by a Semi-transparent Film with a Slit Opening

Spatial interference of acoustically phase-modulated light is explained experimentally and theoretically. If the acoustically phase-modulated light is transmitted by a semi-transparent sheet film with a slit opening, the light diffracted by the slit opening is superposed on the undiffracted background light in the Fresnel diffraction region to yield an acoustically modified interference pattern. This pattern is successfully explained as a result of the partially coherent illumination which is due to acoustic wave modulation. An application of this method is described for measurements of the Raman-Nath parameter and the acoustic wavelength from the variational aspect of the interference fringe pattern.     

Hierarchical-genetic-algorithm-based design of a large scale Fresnel lens for a reading light system with multiple LED sources

A conventional Fresnel lens is suitable to be used in the reading light system due to its features of directing and collecting light rays, as well as its properties of being essentially flat, plastic, lightweight, and cost efficient. However, it is not suitable for a reading light system with multiple light sources. To a reading light system with multiple light sources, a Fresnel lens with suitably designed groove angles can be used to improve the performance of that system in both illuminance and uniformity. Nevertheless, suitable groove angles are rather difficult to find if a Fresnel lens consists of a lot of groove angles and each angle covers a wide range of degrees. We develop a hierarchical genetic algorithm (HGA) to search for a set of optimal groove angles to design a Fresnel lens for a reading light system with multiple light sources from an enormous searching space. In addition, the groove angles of the Fresnel lens are directly derived from a conventional Fresnel lens database. The design goal is to maximize the illuminance and simultaneously maintain the uniformity of light rays incident to a specified reading surface. As a result, we can demonstrate that a HGA really works better than a genetic algorithm and the optimally designed Fresnel lens, indeed, offers a better light-guiding performance than a conventional Fresnel lens for a multiple-LED reading light system.     

Changes in Polarization of a Light Beam with Arbitrary Autocoherence Propagating in a Birefringent Crystal

Based on the Mueller-Stokes matrix formalism and the Wolf autocorrelation functions, a general approach is developed for studying the polarization characteristics of a light beam with arbitrary autocoherence during its interaction with various media. This makes it possible to take into account the dispersion of the medium and the coherence properties of the light field. It is shown that the propagation of a polychromatic light beam with spectrally pure polarization in a certain medium can be described by an integrated Mueller matrix. For a linear phase plate, the matrix elements can be expressed by means of the modulus and the phase of the complex degree of autocoherence. The polarization of a light beam emitted by a black-body radiator and the influence of the dispersion in a KDP crystal in quasi-monochromatic light are discussed as applications.     

液晶显示的红、绿色光对视觉暗适应影响的比较研究

实验以受试持续注视液晶显示屏上较亮的色标后辩认低亮度兰道环所需要的时间作为测量暗适应水平的指标，考察了液晶显示的绿色光强度变化对视觉暗适应的影响，并对红、绿色光在同等强度上的间适应时间了比较。实验结果表明：（1）不同的强度的绿色光对暗适应的影响有显差异，光刺激强度越大，暗适应时间越长；（2）光刺激作用主要集中在视网膜中央宣传员的条件下，等亮度较弱的红光与绿光之间暗适应时间无显差异。     

Application of a wire-grid-mirror liquid-crystal light valve in a nonlinear joint transform correlator

We describe the operation of a wire-grid-mirror liquid-crystal light valve and its use for optical pattern recognition. The nonlinear characteristic of the wire-grid-mirror liquid-crystal light valve is used to implement the nonlinear joint transform correlator. Experimental results and computer simulations show that the nonlinear characteristic of the wire-grid-mirror liquid-crystal light valve can produce a well-defined correlation peak and low output background. The performance of the nonlinear joint transform correlator obtained when the wire-grid-mirror liquid-crystal light valve is used is compared with that of the binary joint transform correlator.     

Generation of three-dimensional dark spots with a perfect light shell with a radially polarized Laguerre-Gaussian beam

The theoretical analyses in this paper show that a highly focused double-ring radially polarized Laguerre-Gaussian beam with a topological charge of 1 (R-LG(11)) can generate a small three-dimensional (3D) dark spot surrounded by an almost 100% uniform light shell in all directions. The cleanness and size of the 3D dark spot, the uniformity and strength of the light shell surrounding the dark spot, and the light efficiency all depend on the truncation parameter β of the R-LG(11) beam and the numerical aperture (NA) of the system. When β=1.6 and the NA is close to its utmost, an almost 100% uniform light shell surrounding the 3D dark spot can be achieved and the dark spot is very clean. If the NA is lowered but β is increased to 1.95, we can also achieve an almost 100% uniform light shell and light efficiency can reach 90%, but the disadvantage is that the center of the dark spot is not too clean. A not-too-clean 3D dark spot, if the light shell surrounding it is very uniform, is acceptable for many applications. Therefore, 3D dark spots surrounded by a high uniform light shell, generated by simply adjusting the truncation parameter of the R-LG(11) beam and the NA of the system, are useful for superresolution fluorescence microscopy, dark spot microscopy, and the dark spot trap.     

Enhanced entanglement in a non-degenerate four-level atom with a parametric oscillator

We discuss the generation and evolution of a macroscopic entanglement light with a subthreshold non-degenerate parametric oscillator, coupled to a vacuum reservoir. The four-level atoms driven by two classical fields interact with the parametric oscillator. The master equation for the cavity modes of the scheme is derived and analyzed, the entanglement properties of the two-mode light generated by this scheme inside and outside the cavity is studied. We show that the light produced by this system is strongly entangled with time evolution inside and outside a cavity.     

Diffractive interconnection between a high-power Nd:YAG laser and a fiber bundle

Beam splitters are used to couple the light of high-power Nd:YAG lasers into a fiber bundle. By the fibers the light is delivered to the workstations in the factory. This technique is used to reduce the costs of the light and to simplify the logistics within the fabrication process. Typically, dielectric beam splitters are used. However, they suffer from a polarization-sensitive splitting ratio. Because the polarization content of a high-power Nd:YAG-laser is not constant in time, polarization-independent beam splitters are of concern. The feasibility of diffractive beam splitters is investigated.     

Generating light with a specified spectral power distribution

A particular version of a spectral integrator has been designed. It consists of a xenon lamp whose light is dispersed into a color spectrum by dispersing prisms. Using a transmissive LCD panel controlled by a computer, certain fractions of the light in different parts of the spectrum are masked out. The remaining transmitted light is integrated and projected onto a translucent diffusing plate. A spectroradiometer that measures the generated light is also attached to the computer, thus making the spectral integrator a closed-loop system. An algorithm for generating the light of a specified spectral power distribution has been developed. The resulting measured spectra differ from the specified ones with relative rms errors in the range of 1%-20% depending on the shape of the spectral power distribution.     

Monitoring photosensitizer concentration by use of a fiber-optic probe with a small source-detector separation

We present a noninvasive method to track the concentration of photodynamic therapy drugs in real time. The method is based on measurements of backscattered and fluorescent light with a steady-state fluorescence spectrometer. The ratio of the fluorescent light to the scattered light is found to be linearly proportional to the absorption coefficient of the photosensitizer. The fiber-optic probe used for the measurements has a small source-detector separation; therefore the measurements could be performed through the working channel of an endoscope.     

卡塞格伦望远镜系统杂散光分析

白天强背景光将通过望远镜系统对后续观测系统产生很强的杂散光。在这种条件下，卡塞格伦望远镜系统杂散光成对称分布，主要来源于望远镜筒壁的漫反射光、马蹄镜的直接反射光和次镜支架的漫反射光。理论分析和数值模拟表明，系统结构中马蹄镜和次镜的作用最大，而观测视场角的增大将导致杂散光通量的急剧上升。     

Polarization characterization of a Mach-Zehnder interferometer

Polarization characterization of a Mach-Zehnder interferometer, based on the state of polarization (SOP) and power measurement at the interferometer output, is presented. We study the SOP and degree of polarization (DOP) of the output light, first as a function of the light power in each arm of the interferometer for a fixed input SOP and DOP, and second as a function of the SOP's in each arm of the interferometer for a fixed input power. Stokes formalism and the Poincaré sphere are used for simultaneous representation of the SOP and DOP, as well as their evolution. It is shown that the SOP and DOP stability and also the output light power are highly dependent on the light source coherence. Knowledge of these different parameters leads to configurations that allow simultaneous control of the SOP and DOP. We can hence realize a quasi-monochromatic nonpolarized light source, which is useful for the polarization-independent characterization of optical components.     

The phenomenon of light concentration by a speckle screen based on a reference-free volume hologram

It is experimentally demonstrated that a speckle screen based on a reference-free volume hologram is capable of concentrating light in the visibility zone. Holographic speckle screens for the projection of images were formed in a bulk photosensitive material based on glycerol-containing dichromated gelatin (DCG). With such screens formed using radiation with a wavelength (0.442 nm) in the spectral range of DCG photosensitivity, it is possible to obtain high-quality image projections using both coherent radiation with a different wavelength and white light. The projection properties of speckle screens were studied, and their ability to concentrate light in the visibility zone was confirmed.     

Near-field magnetooptics in resonant light scattering by a linear nanoprobe

A theory of the magnetooptical scattering of light by a near-field linear probe parallel to the surface of a magnet is presented. The probe is modeled by a cylindrical nanowire supporting long-lived surface plasmons. The scattering of light is considered in the longitudinal magnetooptical Kerr effect geometry (with magnetization parallel to the sample surface and the plane of light incidence). The resonant interaction of the probe + image system is taken into account in the self-consistent approximation of the multiple scattering theory, while the magnetooptical interaction is described in the linear approximation with respect to magnetization. Polarization characteristics of the scattered light and the magnetooptical modulation of light intensity, which are resonantly enhanced by the surface plasmons, have been studied.     

Light scattering by microscopic spheres behind a glass-air interface

Scattering of light from single spheres placed behind a glass-air interface with light incident through the glass is examined. This scattering is investigated for both p- and s-polarized light incident at angles below the glass-air critical angle. The intensity of light scattered into the air half-space from each sphere is measured as a function of scattering angle, and this response is compared in situ with the background scatter produced by the planar substrate. A detailed comparison between data and established theory are thereby obtained. This system is of interest in the field of optical biosensing.     

Optical System of a Sensitometer with a High Range of Non-selective Light Modulation

Reasons for non-selective light modulation in a sensitometer for fundamental research in sensitometry are discussed, particularly with respect to high-range modulation. The underlying optical system described in this paper essentially involves multi-element flat mechanical modulators placed in between light channels of rectangular cross section. A modulator may, with advantage, be constructed in such a way that the outgoing flux changes exponentially with some linear movement, full-scale translation corresponding to exactly one order of magnitude. The number of modulators and light channels used defines the total range of modulation. Using a 650 watt halogen lamp in the illuminating system it is possible to obtain, within the range 1 : 6, 50 000 Lx of light output level with a uniformity better than 2 per cent. Finally, some results measured with the prototype of the instrument are given.     

Ferrodispersion: a promising candidate for an optical capacitor

A ferrodispersion, which comprises micrometer-sized magnetizable spheres dispersed in a ferrofluid, is shown to store retrievable optical energy. It is observed that when such dispersion is subjected to a transverse magnetic field and a linearly polarized monochromatic light with its electric vector perpendicular to the applied field is incident on it, then for a critical static magnetic field of moderate intensity the emerging light disappears. Upon removing the light and then switching off the field, again light of the same frequency and same state of polarization reappears. A time delay between emission of the light and switching off the field is observed. The statistical distribution of this delay is reported. Intensity of the retrieval signal is found to depend on the storage time. This effect is investigated. Storing and retrieval of optical energy will be useful for developing a magnetically tunable optical capacitor.     

Bright entanglement generated in a four-level laser

We discuss the generation and evolution of entanglement in a four-level laser with a subthreshold nondegenerate parametric oscillator. The entanglement properties of the two-mode light generated by this scheme is studied. We show that the light produced by the present system is strongly entangled with time evolution. Especially, with the help of the parametric oscillator, the high intensity of the entangled light between the two-mode cavity can be achieved.     

Extinction of light in Brewster polarizers: a shadowlike phenomenon

A Brewster polarizer in this study is any dielectric plane reflecting surface reflecting light at or near the Brewster angle of incidence. In this paper, we consider an interesting phenomenon observed when we use an extended source of light or a cone of light with its axis incident on the plane surface at the Brewster angle. The resulting reflected light is viewed (a) through an ordinary sheet polarizer and (b) after reflection from another Brewster polarizer. The extinction pattern of light by such a system is in the form of an elongated black shadow in (a) and a nearly circular shadow in (b), respectively. These shadows are explained on the basis and use of the familiar Fresnel equations at a plane interface between two dielectric media. Photographs of the shadows are also presented.