Correlation of light beams scattered at different angles by a ground glass

A quantitative study of the contrast of Young's fringes obtained with a fully scattering element by double exposure technique as a function of the inclination of the incident beam and the effect of varying the scatterer- photographic plate distance upon the γ - θ curve have been presented.     

Determination des lignes de niveau par double photographie en lumiere coherente

Two images of a rough curved object, illuminated by a coherent parallel beam are recorded on the same photographic plate. The incident beam is slightly tilted between the two exposures. In a suitable filtering set-up we observe the depth contours of the object (parallel to the photographic plate); the experimental limitations are discussed.     

The measurement of slope using shearography

This paper presents an optical method which is based on speckle-shearing interferometry for the measurement of the slope at any point of an object. The object under study is illuminated by an expanded laser beam and its image is recorded on a photographic plate placed at the image plane of an image-shearing camera. A second exposure on the photographic film is made after the light source is moved slightly. The resulting photograph yields a fringe pattern which represents lines of constant displacement gradients. Theory of the method as well as some experimental results are presented.     

Determination de rugosite par correlation des speckles dans l'image de la surface diffusante

Two speckle patterns are recorded on a photographic plate which lies in the image plane of a rough surface. The angle of incidence of the parallel beam illuminating the object is slightly varied between the two exposures. It is possible to localize and measure different roughness of the surface by observing suitably the photographic plate. We discuss the experimental setup and the effects of the optical system.     

Measurements of axial displacements undergone by a diffusing object in speckle photography

The speckles of the image plane of an object are both radially shifted and decorrelated when the object is axially translated through an amount ?. We demonstrate that this radial shift, which is related to the position of the pupil of the optical system, disappears when the pupil lies in the back focal plane of the imaging lens. However, if the irradiance of the image plane is twice recorded on a photographic plate which is laterally shifted through ζ_H between the exposures, the minimum value of the contrast of the Fourier fringes exhibited by the plate after processing, gives the value of ? if ? is less than a particular value, ?_M which will be defined. Also we propose a new speckle measurement method in which the fringes are automatically removed when ? is greater than ?_M. We record the image of the object illuminated in convergent light through an amplitude diffuser placed in the Fourier plane of the object. The mean speckle speckle size of the diffuser is equal to the mean size of the speckles generated by the object in its Fourier plane.     

Digital off-axis holography without zero-order diffraction via phase manipulation

By means of manipulating the phase information of the object beam in an off-axis digital holographic setup, we show that it is possible to fully eliminate the zero-order diffraction (ZOD) from numerically reconstructed holograms. Two different approaches are presented. In the first method, we introduce a ground glass on the object path beam to provide a random phase illumination. The subtraction between two holograms recorded with different positions of the ground glass yields a ZOD free hologram. In the second approach, a piece of window glass inserted on the path of the object beam produces a constant phase shift. The subtraction of two holograms, one recorded with and one without window glass generates a new hologram whose numerical reconstruction is ZOD free. Theoretical models and experimental results are shown to validate our proposals. They show that the proposed methods totally remove the ZOD without ruining the object information.     

Numerical computation of in-plane displacements and their detection in the near field by double-exposure objective speckle photography

A model of a rough surface to the scale of the optical wavelength is proposed, with randomly distributed zero-mean Gaussian heights. It is assumed that the aforesaid surface is illuminated by a coherent light beam of homogeneous intensity. An in-plane pure translation of this surface is simulated on a PC by means of the Matlab program. In the near-field optical regions the Fraunhofer approximation and the subsequent FFT are not suitable for application in the generation of a speckle pattern. Hence, with the aim of calculating the translation of the rough surface by means of double-exposure objective speckle photography using the point-wise filtering technique (PWFT), the Fresnel-Kirchhoff integral is first employed to obtain the speckle intensity near the surface on a photographic plate, and then the intensity pattern produced by the diffraction of the plate is determined in the far field (Fraunhofer), which suffices to calculate the modulus of displacement through the Young’s fringes. The results are analyzed according to surface roughness and the sample distance to the recording plane.     

Application of longitudinal multimode laser coherence properties to increase the holographic depth of field

It has been shown that the temporal coherence of a non-mode-locked laser is periodic in 2L/c. It has also been demonstrated that the limitations imposed on the depth of field in holography by the laser coherence properties may easily be overcome by illuminating the object with multiple beams. In such a system each object beam should travel the same distance to the holographic plate as the reference beam, or a multiple of 2L farther. For large objects (which would have large depths of field) multiple beam illumination is necessary anyway, to ensure uniform illumination of the object. In fact the limiting factor with regard to the size of an object and the depth of field should be the laser's power and not its coherence length. An advantage in this method of overcoming conventional limitations is that there is no reduction in the laser's output power as is involved in some other methods of coherence length improvement.     

Spatial coherence of laser light passed through rotating ground glass

The ensemble-averaged spatial coherence of quasi-thermal light, produced by passing a focused laser beam through a rotating ground glass plate, is studied as a function of the illuminated area, the fineness of the glass used, the speed of rotation of the glass, and the laser mode selected as a primary source. It becomes clear that the ensemble-averaged spatial coherence depends strongly upon the illuminated area and on the fineness of the rotating ground glass, and also on the laser mode chosen but not on the speed of rotation of the glass.     

Lensless ghost imaging through the strongly scattering medium

Lensless ghost imaging has attracted much interest in recent years due to its profound physics and potential applications. In this paper we report studies of the robust properties of the lensless ghost imaging system with a pseudo-thermal light source in a strongly scattering medium. The effects of the positions of the strong medium on the ghost imaging are investigated. In the lensless ghost imaging system, a pseudo-thermal light is split into two correlated beams by a beam splitter. One beam goes to a charge-coupled detector camera, labeled as CCD2. The other beam goes to an object and then is collected in another charge-coupled detector camera, labeled as CCD1, which serves as a bucket detector. When the strong medium, a pane of ground glass disk, is placed between the object and CCD1, the bucket detector, the quality of ghost imaging is barely affected and a good image could still be obtained. The quality of the ghost imaging can also be maintained, even when the ground glass is rotating, which is the strongest scattering medium so far. However, when the strongly scattering medium is present in the optical path from the light source to CCD2 or the object, the lensless ghost imaging system hardly retrieves the image of the object. A theoretical analysis in terms of the second-order correlation function is also provided.     

Double exposure, multiple-field particle image velocimetry for turbulent probability density

A particle image velocimeter method is described in which double exposed fields of particles moving in a two-dimensional slice of a steady turbulent flow are photographed repeatedly to build up a statistical ensemble of flow field realizations on a single photographic plate. Each interrogation spot on the plate contains a sample of the probability density function of the two components of velocity that lie in the photographic object plane, assuming paraxial photography. Theory is developed showing how this sample can be measured by two-dimensional spatial correlation analysis, followed by deconvolution to remove the effects of finite particle image size. The probability density measurements are biased inherently against large velocities, but these effects can be minimized and/or corrected.     

Detection of small displacements with the help of an auxiliary diffuser

We propose here a method of detection of small displacements, in which the speckled image of the object is modulated by an additional speckle. Due to this additional speckle, the Fourier transform fringes of the doubly-exposed photographic plate undergo a diminution of contrast when the object suffers a displacement.     

Vibration measurement by vibrating-plate holograms

If a hologram of a vibrating object is recorded on a photographic plate which vibrates synchronously with the object, the reconstructed image produces equi-amplitude fringes of the object vibration, the amplitude of which is reduced by a constant determined from the amplitude of the plate vibration. This phenomenon can be used as a method to extend the measurable range of vibration amplitudes, and some experimental results are shown.     

Observation of a phase object using carrier-frequency photography

A Ronch ruling is photographed through a phase object which produces deformations in the grating lines. The superposition of the straight rulings and the deformed ones on the photographic plate gives rise to a moiré pattern which characterises the phase variations of the object.     

Two-exposure quasi-common-path point diffraction interferometric phase microscopy using a four-step algorithm

A two-exposure nearly common-path point diffraction interferometric phase microscopy (IPM) is presented using polarization modulation and one-step grating shifting to implement quantitative phase imaging. The IPM is constructed by an improved Michelson configuration with a reflective grating, and its frequency spectrum generated by a circularly polarized object beam makes double copies through a beam splitter. One copy is low-pass filtered and reflected by a reflective pinhole mirror to create a reference beam, and the other copy is converted by a polarizer and then reflected by a reflective grating to achieve a 45° linearly polarized object beam. By the combination of a polarizing cube beam splitter with 45° tilted angle and a translation of the reflective grating with a π phase shift, four interferograms with π/2 phase shift can be obtained in two exposures. The standard four-step algorithm can then be used to reconstruct the phase of the specimen. The utility of the proposed method was demonstrated with measurements on a phase plate, cells and an oil drop.     

Essay Review-Scholarly froth and engineering skeletons

Holography is a two-stage process of photography using coherent light from a laser to illuminate the scene. In the first stage a hologram is formed by combining the light scattered from the object and the direct laser beam on a photographic plate. In the second stage a three-dimensional image is reconstructed without the use of lenses, by directing the laser beam through the hologram. Applications of holography include information storage, recording of images in depth, the use of holograms as optical elements, and as a means of performing precise interferometric measurements on three-dimensional objects of any shape and surface finish.     

Speckle photography by birefringent plates

This paper describes a birefringent system with which it is possible to record three laterally shifted speckle images of an object, on a photographic plate. The recording is made with only two exposures. The exposure times and relative positions of the images are adjusted automatically by the birefringent plates.     

组合式力热动态载荷光学窗口的光学特性研究

针对在一定压差及温度梯度等复合环境下工作的大口径光学窗口,提出了一种由光学玻璃与亚克力板组成的光学窗口组合方案,并以热光学分析为基础,对光学窗口整体强度及热环境进行了理论分析计算,得出光学窗口玻璃最小厚度。利用有限元软件将压力场及轴向温度场映射至三维结构模型,计算得到直径为380 mm的光学窗口在不同玻璃厚度下力热耦合的面形变化及成像质量评价指标,并通过相应的环境性试验对仿真结果进行验证。实验结果表明:以K9光学玻璃为原材料的大口径光学窗口在此工作环境下的厚度不小于32.5 mm;当光学窗口厚度为35 mm时,其所受热力学影响可以忽略。因此,35 mm的大口径组合式光学窗口既能满足强度要求,又能满足多光谱相机成像质量要求,为该类窗口的设计提供了依据。     

Production of binary amplitude gratings with arbitrary opening ratio and variable period

A simple double exposure technique is proposed for making binary amplitude gratings with preset opening ratio. Commercially available Ronchi type master ruling is imaged onto the photographic plate by a laser projection system. The controlled lateral displacement of the ruling or the photographic plate between two exposures results in the composite grating with the required opening ratio. A zoom-effect spherical beam projection system is suggested for producing binary gratings with continuously variable period.     

衍射光学器件光线追迹公式的实验验证

本文介绍了一种衍射光学器件光线追迹的方法，并给出了计算公式。作为验证，在实验室里制作了具有连续相位的体全息器件，将其实际再现光斑与计算点列图进行比较。构造透射体全息片的物光为离轴的球面波，始于轴外点Ａ（０，１３２ｓｉｎ８°，－１３２ｃｏｓ８°），参考光为平面光束，其与Ｚ轴夹角为１７°。激光器采用氩离子激光器（Ｓｐｅｃｔｒａ－ｐｈｙｓｉｃｓＭｏｄｅｌ２０２０），波长４８８ｎｍ；干板感光胶为重铬酸明胶（ＤＣＧ），胶层厚为１５μｍ；通光口径３０ｎｍ。测试时把全息片放在干板的位置。挡住物光，让再现光以和参考光路相同的路径平行入射到全息片上，在全息片后垂直光轴放置毛玻璃片，平行光轴移动毛玻璃片，可观察到－１级衍射光的变化。在距离原点的距离分别为（ａ）４０ｍｍ，（ｂ）７０ｍｍ，（ｃ）８７ｍｍ，（ｄ）９５ｍｍ的地方用ＣＣＤ拍摄了衍射光的形状，与程序计算的点列图在形状和大小上都吻合