Analysis of a partially coherent optical correlator in the presence of phase defects at the input plane

The effects of phase defects at the input plane of an optical correlator on the performance of the system under partially coherent illumination is investigated. The correlation signal-to-noise ratio (SNR) is evaluated as the criterion for the performance of the optical system. We study the effects of both spatially and temporally partially coherent illumination on the distorted correlation signal. It is shown that the output SNR can be increased by relaxing the coherence requirements of the system. The SNR dependence on noise variation is also investigated. It is found that the correlator becomes less sensitive to noise variations under partially coherent illumination.     

Synthesis of spatial coherence

The mutual intensity function plays a major role in characterizing quasi-monochromatic, partially coherent optical signals. We propose to use the mutual intensity as a carrier of information to avoid speckle noise in coherent illumination systems and to permit the use of complex functions that are prohibited spatially incoherent sources. To do this we require methods for encoding the information as a coherence function. An optical system for synthesizing a beam with a given mutual intensity function is proposed. The optical system permits the synthesis of any desired mutual intensity function. The illumination is supplied by a quasi-monochromatic, spatially incoherent source. Experimental results demonstrate the performance of this system for several cases.     

Illumination with a moving light source

Image formation is discussed under the condition that an object is illuminated with a moving light source and a time-averaged image is observed. An optical system with such illumination works as if the object were illuminated with spatially, partially coherent light from a certain fixed source.     

Supercontinuum laser illumination applied to traditional optical flow imaging methods

The schlieren method of refractive flow visualization traditionally requires non-coherent illumination in order to avoid problems with coherent artifact noise and binary cutoff by the knife-edge. Related shadowgraph and Wollaston-prism schlieren-interferometer methods, however, work well with light sources of high spatial coherence. Here we apply a supercontinuum laser as a light source for these methods, providing spatially coherent white-light illumination. Excellent results are obtained with shadowgraphy and schlieren-interferometry, but the schlieren method still requires a modified cutoff in place of the traditional knife-edge for laser illumination. Once they become widely available, supercontinuum lasers will find frequent use in these optical instruments, especially the schlieren-interferometer.     

Influence of Partially Spatially Coherent Illumination on the Measurement of Two-dimensional Correlation Function

A coherent optical filtering is often applied to the measurement of correlation function of two-dimensional patterns. The present report treats the influence of spatial coherence on such an optical filtering. A general formula for optical filtering with partially spatially coherent illumination is obtained. The intensity distribution of correlation in the output image plane for several special cases is calculated, where different kinds of coherence conditions of illumination in the process of holographic recording of a filter, or of filtering are assumed. An experiment is performed to verify the theory.     

Image-plane speckle in partially coherent illumination

Expressions are derived for the first and second order statistical properties of speckle formed in the image of a diffuse object when the illumination is both temporally and spatially partially coherent. Sunlight falls into this illumination category, and we are therefore able to deduce conditions under which sunlight speckle will show best contrast.     

在LiNbO3:Fe晶体中写入Y结孤子的实验研究

采用振幅掩模穿过部分空间非相干光的方法产生一暗迹,将暗迹成像在晶体前表面,得到入射暗迹半高宽为16.75 μm,入射光功率为400 μW.基于LiNbO3:Fe晶体的强光伏效应,在无背景光辐照时,在晶体内写入一对部分空间非相干Y结暗光伏孤子.实验结果表明：在无背景光辐射时可以在LiNbO3:Fe晶体内写入部分空间非相干Y结孤子.     

Optical autowaves in photorefractive ferroelectric crystals

The effect of appearance of traveling structures, referred to as scattering autowaves, under illumination of photorefractive media by coherent light under certain conditions (power, wavelength, and focusing of pump radiation) is theoretically described. A model is proposed that takes into account both longitudinal and transverse photovoltaic currents in crystals with a spatially isotropic distribution of seed permittivity fluctuations.     

Fourier holograms recorded and decoded in polychromatic light

This paper describes a recording and reconstruction method applied to two-dimension Fourier holography, in which the illumination at the recording stage is spatially coherent and temporally incoherent. The various chromatic components of the information to be recorded in the hologram are spread along a direction orthogonal to the entrance slit of a spectroscope that behaves as scanning pupil performing a chromatic coding. The message, both spatially and temporally coded, can be reconstructed by using a conventional process, the light source being still polychromatic.     

环型孔成像系统在部份相干光照明下对两个点物之分辨

在部份相干光照明下的环型孔成像系统，对两个点物之分辨，按照Ｓｐａｒｒｏｗ判据作了分析和研究，将两点之分辨作为两个参数的函数进行讨论－其一为照明光的空间相干条件，其二为环型孔的中心阻挡，在与圆型孔和完全相干照明的情况比较之后指出，环型孔和部份相干照明情况具有更高的两个点物的分辨本领。     

A Novel OADM Based on Fiber Gratings

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Noise performance of a white-light optical signal processor

A study of the effects of spatially and partially coherent illumination on the noise performance of an optical processor is presented here. Noise arising from defects in the object plane and the Fourier plane are considered separately. Two important types of noise are analyzed in detail: (a) amplitude noise and (b) ramdom phase noise. The results illustrate that the effects of the object phase noise can be reduced when the requirements on spatial coherence are relaxed. Also, the noise at the Fourier plane can be effectively eliminated when a spatially incoherent light source is employed.     

Coherent super-resolution microscopy via laterally structured illumination

Theory describing a super-resolution microscopy experiment using temporally and spatially coherent structured illumination was developed, and used to derive a method for processing experimental data. Numerical simulations were performed to verify that the method can, in principle, produce super-resolved images that are exactly equivalent to an image processed by a system with a much larger aperture (that is, the correct weighting between different regions of the image spectrum is maintained). The process was then demonstrated experimentally, showing a factor of two improvement in resolution over a diffraction-limited, coherently illuminated, microscope.     

Design of diffractive axicons for partially coherent light

We propose a novel method of designing diffractive axicons for use in spatially partially coherent illumination. The design procedure is based on the results obtained by the stationary-phase method. The technique leads to a coherence-dependent differential equation with appropriate boundary conditions for the axicon phase function. We demonstrate the method with annular-aperture axicons generating extended focal line segments of uniform on-axis intensity.     

Coherent transmission and reflection of a two-dimensional planar photonic crystal

A method for modeling the radial distribution function for particles of a two-dimensional planar photonic crystal in the form of a monolayer of spatially ordered monodisperse spherical particles is proposed. The coherent transmission and reflection coefficients for layers under normal illumination are calculated in the quasi-crystalline approximation of the multiple wave scattering theory. The dependence of the coherent transmission and reflection of the layer on the degree of ordering of the spherical particles is investigated. The influence of the long-range order on the coherent transmission and reflection coefficients for layers with triangular, square, and hexagonal lattices is estimated. Monolayers of weakly absorbing dielectric and strongly absorbing metallic particles are considered.     

Coherent beam amplification with a photorefractive liquid crystal

Coherent amplification of a signal beam by a strong pump beam is observed in thin films of fullerene-doped nematic liquid crystal. Exponential gain constants as high as 2890 cm(-1) with no phase cross talk are achieved at low applied dc bias voltage and pump beam intensity. The underlying mechanism is the electro-optically induced spatially reorientation of the liquid-crystal axis and the resultant phase-shifted index grating required for two-beam coupling.     

Entangled-photon imaging of a pure phase object

We demonstrate experimentally and theoretically that a coherent image of a pure phase object [implemented by a microelectromechanical system (MEMS) micromirror array] may be obtained by use of a spatially incoherent illumination beam. This is accomplished by employing a two-beam source of entangled photons generated by spontaneous parametric down-conversion. One of the beams probes the phase object while the other is scanned. Though each of the beams is, in and of itself, spatially incoherent, the pair of beams exhibits higher-order interbeam coherence.     

部分相干光学成像系统的光学传递函数和像质评价准则

根据光学成像理论，建立了部分相干成像光学系统的光学传递函数。该函数与非相干成像光学系统传递函数相同，因而部分相干成像和非相干成像两者的光学系统波面像差公差标准也是相同的。这一点解释了显微镜光学系统的光学设计惯用法则：镜头像差公差标准的选择，并不因为采用成像照明方式的不同而有所差异。     

空间周期相干光照明下的自成像现象及Lau效应

借助模糊函数理论分析了空间周期相干光照明产生的自成像现象及Ｌａｕ效应。理论分析结果表明：当照明光源满足一定条件时，会出现自成像现象及Ｌａｕ效应。根据分析结果讨论了这些现象的可能应用。     

A physical model of the action of low-intensity laser radiation on biological objects

A new model of the action of low-intensity laser radiation (LILR) on biological objects on the cellular level is proposed. The model implies that, because the laser radiation is coherent, the illumination in the bulk of a biological object can acquire a spatially periodic character (in the form of an interference pattern or speckle structure), with the period of alternating dark and light regions being comparable with the size of cells or cell organelles. Under these conditions of high-gradient illumination, an electrical field can arise (the Dember effect) that can change the character of photostimulated reactions and the membrane charge state not only in the cell itself but also in its organelles, which leads to shifts in the life cycle of cells (and/or bacteria).