Dynamic optical correlation using localized holography

A new technique for optical correlation using gated holographic recording is demonstrated. Several persistent holograms are localized within separate slices as close as 33 microm apart along the crystal. Individual holograms can be dynamically erased and rerecorded with no need to refresh all other recorded holograms. Experimental results showing the correlation capability, cross talk, shift invariance, and dynamicity of the localized holographic correlator demonstrate unique performance and capabilities for these correlators.     

Enhancement of sensitivity of measurements of the holographic lateral-shear interferometry in studies of fast processes

The possibility of enhancing the sensitivity of measurements upon visualization of temporal variations of a phase object by means of optical processing of the holographic lateral-shear interferograms, without the necessity of detecting the original holographic interferograms under nonlinear conditions, is considered. In rewriting the original holographic interferogram, it is advisable to change the orientation of the holographic fringes and to record the secondary holograms under nonlinear conditions. The proposed method for increasing the sensitivity of measurements was used to visualize variations of thickness of a polymethyl methacrylate plate in the course of its thermal treatment.     

Moire processing of acoustic field holograms

A moiré method for processing optical image-plane holograms of acoustic fields is introduced. Derivatives of acoustic pressure with respect to space, time and other system variables can be obtained by this extension of holographic interferometry methods. The new method is employed to obtain simultaneous, independent measurements of acoustic pressure and particle acceleration. It is also demonstrated that moiré processes can improve the sensitivity of optical, whole field measurements at least 30 times.     

Digital particle holographic system for measurements of spray field characteristics

A digital particle holographic system for measurements of spray fields is presented. A double exposure hologram recording system with a synchronization system for time control is established, resulting in digital holograms that can be quickly recorded. To process recorded holograms, the correlation coefficient method is used for focal plane determination of particles. To remove noise and improve the quality of holograms and reconstructed images, a Wiener filter is adopted. The two-threshold and image segmentation methods are used for binary image transformation. For particle pairing, the match probability method is adopted. The proposed system is applied to a spray field, and three-dimensional velocities and sizes of spray droplets are measured. Measurement results from the digital holographic system are compared to those made by laser instruments, which prove the feasibility of the proposed in-line digital particle holographic system as a good measurement tool for spray droplets.     

State of the art of color interferometry at ONERA

At ONERA-Lille center a lot of studies have been conducted to characterize complex flows using an optical method based on differential interferometry with Wollaston prism and white polarized light source. Several applications are presented in two-dimensional and axisymmetric flows and in a gaseous mixture where the two gases interface is submitted to acceleration. Then, real-time color holographic interferometry (RCHI) has been developed to obtain the refractive index itself in two dimensional wake flow. The last improvements concern the extension of this method for analyzing three dimensional flows. The authors present a specific setup defined in a single sight direction, the aim being to reproduce the same optical setup along several sight directions, each shifted by a given angle. This optical technique uses reflection holograms where the diffraction efficiency of plates is strongly influenced by the variations in the gelatin thickness produced during the holograms treatment. Problems are discussed and solutions are proposed to control the gelatin shrinkage for two different types of used holograms. The results obtained in a one sight direction make it possible to build in the future an optical setup allowing several simultaneous line-of-sight optical measurements.     

Spectral selectivity of holographic mirrors recorded in an attenuating medium

Numerical simulation of the optical properties of unslanted reflection holographic gratings (holographic mirrors) is made by the characteristic matrix method. The holograms are recorded in an attenuating medium but the reconstruction is that of pure phase structures in which the refractive index depends exponentially on the exposure. The dependence of the hologram spectral selectivity on medium absorption, amplitude ratio of the two interference waves and recording linearity is studied.     

High-sensitivity moire flaw detection for comparison of periodic composite structures

For the moire visualization of macroscopic defects in composite periodic structures by comparing a structure under study with the reference, it is proposed that rerecorded moire patterns from each of the substructures be used as reference ones. The use of the rerecorded moire patterns obtained by filtering complex conjugate orders of diffraction improves the sensitivity of the method.     

国产KL全色全息干板感光特性研究

为了用国产KL型全色全息干板制作真彩色反射全息图,对KL全息干板的感光特性进行了实验研究.介绍了实验的光路,化学处理方法,三基色的选择.测试了底片单波长记录的感光特性和波长灵敏度,对三基色波长记录的特性进行了实验和分析,结果表明KL全息干板可用于记录真彩色反射全息图.     

Study on the simplified phase-shifting digital holographic microscopy

In this paper, a new simplified technique for effectively eliminating the zero order and the conjugate virtual image in digital holographic microcopy, which makes use of two-step phase-shifting method of just recording two holograms and an intensity image of object wave, is proposed. Meanwhile, combined with the principle of making full use of spatial bandwidth of the CCD sensor by in-line lens-less Fourier holographic recording geometry, the theory and experimental methods to increase the resolution of the reconstructed image in digital holography by using phase-shifting technique are detailedly analyzed. At end, the validity and availability of this technique has been demonstrated through the off-axis and in-line Fourier transform recording geometry. The study provides some theoretical and experimental guidance for the design and operation of a digital holographic microscopy system.     

Two-photon induced photorefraction in undoped lithium tantalate crystals with different compositions

Two-photon interband photorefraction in undoped lithium tantalate crystals with composition ranging from 47.95 to 49.6 mol% of lithium oxide was demonstrated at the wavelength of 532 nm. The photorefractive properties were examined with holographic method. Two-photon holograms were recorded with high holographic sensitivity, large refractive index change, and fast hologram writing time. Permanent changes of the refractive index have been obtained. These holograms can be read nondestructively at the wavelength of 660 nm using heterodyne method. Holographic characteristics strongly depend on composition.     

Investigation of the spectral selectivity of volume holograms with femtosecond pulsed radiation

A method for studying the parameters of high-selectivity volume holograms and photonic crystal structures using ultrashort pulsed radiation in a wide spectral range is developed. The experimental system and measurement procedure are described. The results of determination of the diffraction efficiency and spectral selectivity of holographic gratings with spatial frequencies of 360 and 640 mm^?1 are presented. The parameters of the holograms determined by the method proposed and by the conventional techniques based on the use of continuous laser radiation are found to coincide.     

Three-dimensional solid particle positions in a flow via multiangle off-axis digital holography

We present a new development of digital off-axis (OA) holography for determining the instantaneous solid particle positions in a flow. This holographic imaging method uses a CCD camera for the simultaneous digital recording of two views of digital Fresnel OA holograms on the same support. The reconstruction is obtained numerically. The method provides two orthogonal views of the same flow area of interest at the same instant. It helps to overcome the depth of focus problem existing for the particle image reconstructions and that is inherent to the method. This method has the advantage of being simpler than the methods presently available, and it does not suffer from the flaws of in-line holographic configuration. Furthermore it is completely digital and thus avoids the cumbersome analysis following hologram recording. Digital holograms and digital reconstructions are obtained for solid particles of 200 mum moving into a stirred flow cell of 5 cm(3).     

数字全息显微术中重建物场波前的相位校正

数字全息显微术克服了传统光学显微术无法直接提取样品相位信息的缺点,可以对活体细胞组织等相位型生物样品进行定量测量和有效观察。但在数字全息显微成像过程中,像场弯曲会对再现像相位分布的测量和观察产生影响。提出一种采用相位相减来校正数字全息再现像像场弯曲的方法。通过在样品加入前后两次拍摄全息图,并对数值重建像分别进行去包裹运算再令其相减,即可实现对像场弯曲的有效校正,对蝉翼和大蒜表皮细胞等相位型物体进行测量,并采用数值校正和相位相减两种方法对像场弯曲进行校正。与现有的数值校正方法相比,利用相位相减获得样品三维相位信息的方法更为简单、可靠,是校正像数字全息再现场弯曲的有效方法。     

Real-time holographic interferometry using superposed compensating holograms

Superposed compensating holograms are shown to be a promising tool for solving a number of problems in real-time holographic interferometry, in particular, obtaining of interference patterns with fixed parameters of reference fringes and adjustment of the measurement sensitivity. The proposed approach is tested through visualization of the melting of a PMMA planar sample by means of lateral shear holographic interferometry.     

Holography and micro-holography of particle fields: A numerical standard

Holography is an ‘old’ technique for studying the behavior of clouds of droplets which finds a new interest with CCD cameras and real-time numerical reconstruction. Furthermore, the continued progress in camera characteristics (sensitivity, pixel number, digitalization level, and so on) opens the way to more accurate recording of the interference field. To gain a deep understanding of the technique, as well as an evaluation of the performance and limitations of digital holographic particle measurements under various conditions, standard holograms are required. In this paper, a general numerical standard of holograms of fields of particles based on rigorous near-field Lorenz–Mie scattering theory is presented. This theory makes possible the computation of holograms of fields of particles with an arbitrary number of particles of arbitrary size, arbitrary refractive index, arbitrary recording distance (near-field or far-field), and an arbitrary collecting angle (forward, off-axis, or backward scattering light). Several calculation examples are also given for the code validation and possible applications, including a new possible way to simultaneously measure the size, location, and refractive index of particles.     

Measurement of Slopes of a Deformed Object Corresponding to Different Directions with Digital Holography

A digital holographic method that can be used for the simultaneous measurement of slopes of a deformed object in different directions is described in this paper. In this method, two holograms are recorded numerically under the normal and deformed states of the specimen, and two object waves are numerically calculated from these two holograms. The slopes corresponding to different directions are measured by superposing the two object waves with appropriate shifts. It is a superior method in regard to the simple experiment setup, the flexibility in handing the data, and the high quality phase maps.     

Measurement of Slopes of a Deformed Object Corresponding to Different Directions with Digital Holography

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全息透镜用于彩色胶片全息高密度存储

本文提出一种利用全息透镜实现彩色胶片全息高密度存储的方法。用红、绿、蓝三基色激光分别记录三个焦距相同的全息透镜,用三个全息透镜依次用三基色波长记录胶片的傅氏全息图,用原参考光照明再现,可合成彩色像。     

Wavelength-scanning digital interference holography for optical section imaging

We propose and experimentally demonstrate a simple digital holographic method that allows reconstruction of three-dimensional object images with a narrow depth of focus or axial resolution. A number of holograms are optically generated by use of different wavelengths spaced at regular intervals. The holograms are recorded on a digital camera and reconstructed numerically. Multiwavelength interference of the holograms results in images of the contour plane whose thickness can be made arbitrarily narrow. Objects at different distances from the hologram plane are imaged clearly and independently, with complete suppression of the out-of-focus images. The technique is available only in digital holography and should have useful applications in holographic microscopy.     

A new multiple-exposure scheme for full-color full-parallax holographic stereogram

We propose a new multiple-exposure scheme for full-color full-parallax holographic three-dimensional (3D) printer, in which two of three primary-color holograms are exposed at the same location on the recording medium. In this paper, the optimal combinations of colors for multiple exposure are experimentally derived. In addition, it is shown that the proposed method enables higher brightness, better color reproducibility, and high resolution through the experiment of recording and measurement of color-chart holographic stereogram.