On the possibility of phase conjugation of cw multifrequency HF-laser radiation using Bragg scattering in a HBr-Xe mixture

We consider an approach to phase conjugation (PhC) of multifrequency radiation of a cw HF chemical laser (HF-CCL) using Bragg scattering in a resonantly absorbing medium. The choice of working components of this medium, HBr and Xe, is analyzed at length. Numerical calculations are performed employing a mathematical model presented in this paper; the reflectivity is plotted as a function of the component concentration ratio, the intensities of waves determining the volume hologram in a WFI cell, and the angle of their convergence. We consider the problem of cooling the medium by mixture circulation. The calculations show that the approach suggested is a candidate for implementing the PhC of a high-power multifrequency HF-CCL.     

Synthesis of multifrequency optical holograms of rotating objects

A two-channel system for synthesizing two-dimensional complex multifrequency optical holograms of rotating objects was developed. In the object irradiation (longitudinal) direction, a hologram is synthesized due to multifrequency laser radiation, and in the transverse direction, the synthesis is provided by object rotation. The object image is reconstructed in the plane coinciding with the plane of its rotation. The resolution of the synthesized hologram in the longitudinal direction is determined by the frequency bandwidth of the laser radiation, and in the transverse direction, the resolution is determined by the initial laser-radiation frequency and the angle of object rotation during the time of hologram synthesis. Using a digital simulation, the degree of isoplanarity of the multifrequency system for synthesizing holograms of rotating objects and its noise immunity under conditions of phase noises were analyzed.     

Effective method of phase conjugation of multifrequency radiation in “pseudo”-four-wave interaction

The possibility is considered of formation of a multifrequency-radiation wave front (with a wide line spectrum in the interval , +), reversed with respect to the wave front of a signal wave of frequency ₀ unequal to the frequencies in the indicated spectrum. The wave front reversal (phase conjugation) is achieved by diffraction of a multifrequency light wave in a direction counter to that of the signal, on a three-dimensional dynamic hologram produced by electromagnetic fields of frequency ₀ in a resonant medium (with thermal nonlinearity) that is fully transparent to the multifrequency radiation. A single direction of the radiation diffraction at all frequencies of the spectrum is ensured by preliminary passage of the initial multifrequency wave through a simple dispersive prism that deflects the direction in each spectral line in proportion to the frequency change. The basic equations describing a similar phase conjugation method are derived, and the efficiency of the conjugation are estimated using as an example multifrequency emission of a chemical cw HF laser.P. N. Lebedev Instiute of Physics. Translated from Preprint No. 205 of the lebedev Institute of Physics of the Academy of Sciences of the USSR, Moscow, 1989.     

基于数字闪耀光栅的位相全息图光电再现优化

针对利用液晶空间光调制器（LC-SLM）进行全息图光电再现过程中,再现像面存在多级衍射像造成单一像能量利用率低的问题,提出了一种在位相全息图中加载数字闪耀光栅的方法,以提高全息图光电再现中单一衍射像的衍射效率.分析了闪耀光栅作为衍射光学元件的特性及其对光波进行位相调制的原理,并阐述了在LC-SLM中加载数字闪耀光栅对位相全息图光电再现时像面能量分布的影响.搭建了基于LC-SLM的位相全息图光电再现实验系统.理论分析表明：在其他条件不变的情况下,加载竖直（或水平）槽向周期为2 pixels的数字闪耀光栅可使 关键词： 全息光电再现 位相全息图 数字闪耀光栅 液晶空间光调制器     

Spatial Filtering of Holographic Lateral-Shear Interferograms for Wave-Front Control. The Use of a Higher Approximation

Recording and reproduction of a double-exposure lensless Fourier hologram of a mat screen for wave-front control is analyzed in a third approximation. It is found theoretically and experimentally that aberrations in the reference channel limit the sensitivity range of a lateral-shear interferometer, and errors of control due to aberrations in the objective channel can be eliminated using spatial filtering of the diffraction field in the hologram plane at the optical axis.     

Measurement for Scattering Media by Synthesis of Optical Coherence Function with Super-Structure Grating Distributed Bragg Reflector Laser Diode

The application of the technique of synthesis of optical coherence function for detection in scattering media is investigated. By modulating the optical frequency, the technique synthesizes the coherence function into a delta-function-like peak at an arbitrary location, and thus can select interferometrically the information at that location. The location is adjustable by the modulation parameter or additional phase modulation. A multi-section super-structure grating distributed Bragg reflector laser diode (SSG-DBR-LD) of THz-order tunable range is employed to enhance the spatial resolution for suppressing the multiple scattering from locations other than that detected. In a preliminary experimental demonstration, a reflectometry of 550 μm spatial resolution was achieved and was used to detect scattering media.     

散射介质超衍射极限技术研究进展

综述了已有散射介质超衍射极限聚焦和成像技术的研究现状及进展。首先介绍了这一领域的研究背景及意义,以及已有超衍射极限成像技术的发展现状;然后给出了应用于超衍射极限成像的散射介质定义;其次分析了时间反演技术在声学、微波领域聚焦上的应用,介绍了时间反演法在光学领域超衍射极限聚焦应用中的实现方法,总结了散射介质加入到光学系统中的作用,分析了利用反馈控制调节和光学相位共轭方法进行散射介质超衍射极限聚焦方法的特点;讨论了基于空域和空频域传输矩阵测量的散射介质宽场成像方法及在该目的下的散射介质制备方法;最后给出了散射介质光学超衍射极限成像技术研究前景及展望。     

基于光热敏折变玻璃的透射型体布拉格光栅角度选择性研究

采用Kogelnik耦合波理论讨论了透射型体布拉格光栅(TVBG)的角度选择特性;结合分波面双光束干涉法和两步热处理法在光热敏折变玻璃中制备了周期为1 μm的TVBG,TVBG相对衍射效率可达91.1%;利用发散光束研究了TVBG的角度选择特性,验证了TVBG具有良好的角度选择特性,可以应用于角选择滤波,抑制中高频调制,提高激光的近场均匀性。     

Synthetic aperture fourier holographic optical microscopy

We report a new synthetic aperture optical microscopy in which high-resolution, wide-field amplitude and phase images are synthesized from a set of Fourier holograms. Each hologram records a region of the complex two-dimensional spatial frequency spectrum of an object, determined by the illumination field's spatial and spectral properties and the collection angle and solid angle. We demonstrate synthetic microscopic imaging in which spatial frequencies that are well outside the modulation transfer function of the collection optical system are recorded while maintaining the long working distance and wide field of view.     

利用数值再现实现彩虹全息色差评价

为了在计算机制彩色彩虹全息图输出之前定量得到再现像的色彩保真度,提出了一种采用数值再现进行色差评价的方法.首先对彩虹全息图进行了频谱分析,得到再现参量与频谱分布之间的关系;然后采用频域滤波算法实现彩色彩虹全息图数值再现,得到再现像的相对功率谱分布;最后采用CIE1976UCS均匀颜色空间对再现像色差情况进行了计算.设计了7个色块并制作了计算机制真彩色彩虹全息图,以金卤射灯作为照明光源进行了光学再现实验,给出实验结果及分析.研究证明了采用数值再现方法实现对计算彩虹全息再现像光谱分布和色差进行计算分析是一种快速经济的方法.     

Eliminate the influence of zero-order diffraction for wavefront reconstruction with selectable magnification in digital holographic

The objective surface is considered as the scattering plane; frequency spectrum of a digital hologram transmission light is studied when the reference light and reconstruction wave are spherical waves. The relation between relevant parameters and the object light, conjugate object light and zero-order diffraction wave frequency spectrum distribution. The research results show that: each frequency spectrum of the diffracted wave broadens to various degrees as the radius of the reconstruction wavefront decreases, and frequency aliasing is generated under certain conditions. Based on the research results, a new method that carries out high-pass filtering processing without zero-order diffraction interference upon digital hologram is proposed and the reconstruction experimental proof for eliminating the interferential changeable magnification wave is given.     

Dynamic recording of χ<Superscript>(2)</Superscript> holograms with multifrequency object and reference waves

The transformation properties of images formed by inertialess dynamic χ⁽²⁾ holograms recorded by multifrequency reference and object beams are studied theoretically and experimentally. The regular features of the spatial localization and scales of holographic images obtained with different frequency combinations of the reference and object image-forming beams are ascertained. It is shown that, in the general case of an arbitrary variation in the ratio of these frequencies, the reconstructed images of an object point source are localized on a segment of a straight line, which we referred to as the locris. The slope of the locris does not depend on the frequency ratio of the reference and object beams, and its endpoints are specified by the positions of the reference and object sources. The possibility of obtaining of achromatic holographic images for noncollinear multifrequency interactions is demonstrated. The conditions for the noncollinear phase matching of interacting waves in a KTP crystal, as well as for simultaneous attainment of phase matching for selected frequency combinations, are determined. The important role of controlling the shape of wavefronts in experiments with frequency conversion of radiation in the reference beam by stimulated Raman scattering of light is ascertained.     

Resolution in X-ray Holography

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纯位相信息自聚焦计算全息匹配滤波器

本文介绍一种用计算全息方法制作的纯位相信息自聚焦匹配滤波器。它在编码时取滤波函数的振幅为１,仅对位相进行编码;并通过对傅里叶谱加入二次位相因子代替傅里叶透镜,使其具有自聚焦功能。与常规的方法（光学全息法或计算全息法）所获得的匹配滤波器相比较,具有原理上更合理,滤波器的制作和匹配光路更简单,也更容易实现匹配等特点。所得到的匹配实验结果也很清晰,这与理论是完全符合的。     

位相差异波前传感技术在大型空间光学相机中的应用

在位相差异技术原理的基础上,利用现有平台,通过室内实验以及室外推扫成像试验,检验了位相差异技术波前反演的效果.试验表明:以干涉仪实测波前与反演波前的残差均方根误差作为评价标准,基于位相差异技术的波前反演精度可达1/40λ(λ=632.8nm);同时,利用反演波前进行的图像复原滤波能够大幅改善推扫退化图像的品质,复原后图像信噪比的提升量优于40%,奈奎斯特频率处调制传递函数的提升量超过80%.间接地证明了位相差异波前反演技术的实际效能,为位相差异波前反演技术的空间应用奠定了基础.     

Fast phase retrieval in slightly off-axis digital holography

In this study, three efficient algorithms are proposed for fast phase retrieval in slightly off-axis digital holography using spectrum cropping, spatial multiplexing, and complex encoding. In the first algorithm, the real spectral order of the subtracted hologram is filtered and cropped, and the number of pixels is decreased in the subsequent retrieval operations. In the second algorithm, two sequential subtracted holograms are digitally phase shifted and spatial multiplexed into one synthetic hologram, and thus only one inverse Fourier transformation is then required. In the third algorithm, two sequential subtracted holograms are encoded separately into the real part and the imaginary part of a complex hologram. Two cross-correlations can be used to reconstruct the phase, thereby improving the utilization of the spectrum. The three new algorithms speed up our previously proposed retrieval method with the assistance of specimen-free holograms. Our experiments demonstrated the validity and improved time requirements of the proposed methods.     

液芯光纤中基于多线抽运调制的带宽可控平顶布里渊增益谱

提出在CS₂/CCl₄混合介质液芯光纤中利用多线抽运调制 技术实现带宽可控平顶布里渊增益谱的方法, 理论研究了抽运光谱线间距、谱线强度和芯液介质混合比对布里渊增益谱的影响, 得到了带宽可控平顶增益谱的条件. 结果表明, 采用一个强度或相位调制器, 基于单频和多频调制技术产生2–9条抽运光谱线, 通过控制谱线间距和各谱线强度比, 并改变CS₂体积分数, 获得了增益带宽在50 MHz–2 GHz 范围内可控的平顶增益谱. 该方法操作简便、带宽调控范围大, 可用于高增益低畸变布里渊放大, 满足微弱光信号探测和慢光系统的应用需求. 关键词： 受激布里渊散射 布里渊增益谱 多线抽运调制 液芯光纤     

Analysis of the form of ultrashort pulses by spectral nonlinear interferometry

A new method for recording the phase structure of ultrashort optical pulses is proposed that makes no use of a reference pulse. Using three-wave interactions in a nonlinear optical medium, a wave of spectral decomposition of an ultrashort pulse is transformed into a monochromatic wave. The spatial phase structure of this wave contains information on the phase structure of the pulse spectrum and on the pulse form. This structure is analyzed by shearing interferometry.

     

结合线性回归的离轴数字全息去载波相位恢复算法

为实现仅用一幅离轴数字全息图便能直接恢复相位,提出一种利用空间载波相移技术(spatial carrier phase shift, SCPS)和线性回归相结合的离轴数字全息去载波相位恢复算法.首先,利用SCPS将一幅离轴数字全息图分为四幅含有载波相移的全息图,其中载波相移由沿行、列两个方向的正交载波所引入;然后,将四幅载波相移全息图作为输入,将所求物体相位和两个正交的载波作为未知量,结合最小二乘法和线性回归同时求出载波和相位信息.相较于已有的去载波技术,本算法无需背景全息图作为参考,便可准确地去除载波,实现高质量的相位重建.本文结合数值仿真和具体实验结果验证本算法的有效性和优越性.     

Electron density characterization by use of a broadband x-ray-compatible wave-front sensor

The use of a Hartmann wave-front sensor to accurately measure the line-integrated electron density gradients formed in laser-produced and z-pinch plasma experiments is examined. This wave-front sensor may be used with a soft-x-ray laser as well as with incoherent line emission at multikilovolt x-ray energies. This diagnostic is significantly easier to use than interferometery and moiré deflectometry, both of which have been demonstrated with soft-x-ray lasers. This scheme is experimentally demonstrated in the visible region by use of a Shack-Hartmann wave-front sensor and a liquid-crystal spatial light modulator to simulate a phase profile that could occur when an x-ray probe passes through a plasma. The merits of using a Hartmann sensor include a wide dynamic range, broadband or low-coherence-length light capability, high x-ray efficiency, two-dimensional gradient determination, multiplexing capability, and experimental simplicity. Hartmann sensors could also be utilized for wavelength testing of extreme-ultraviolet lithography components and x-ray phase imaging of biological specimens.