二维彩色彩虹像面全息图记录的一种新方法

本文提出了利用液晶光阀和单色激光进行彩色全息图记录的方法.借助于液晶光阀非相干-相干转换的功能,采用新的彩虹全息术,获得了记录于同一块干版上的原彩色目标由红、绿、篮三色所成的三个基色彩虹全息像.用白光透射再现,得到原彩色图的真彩色全息像.这种方法是液晶光阀、条形散斑屏在图像处理中的一种特殊应用.     

High speed holocinematography using spatial multiplexing for image separation

Up to eight holograms are successively recorded at maximum repetition rates of 20kHz. A multiply Q-switched ruby laser is used to produce the series of coherent light pulses for hologram exposure. All holograms are recorded on the same plate. Image separation of different holograms is achieved by spatial multiplexing using a rotating disk with apertures directly in front of the holographic plate. The performance of the technique is demonstrated by reconstructions of a hologram series taken of laser produced cavitation bubbles following optical breakdown in water.     

Efficient and flexible laser beam scanners constructed from volume holograms

We combine the scan flexibility of computer-generated holographic laser beam scanners with the high diffraction efficiency of volume phase holograms to produce a new type of “holo-scanner”. The scanner-hologram consists of numerous, small, volume hologram facets recorded in dichromated gelatin films and produces an arbitrary output pattern with greater than 90% light efficiency. Experimental results from discrete point, continuous line, and 3-D scanners are shown. Multi-wavelength scanners are also considered. This paper is based on the concepts presented in the preceding paper on “computer-interferometric holograms used for laser beam scanners”.     

Influence of light polarization on the diffraction efficiency of TIR holograms

Normally when forming a TIR hologram two interference gratings are stored in the recording medium. The object beam interferes with the incoming and with the reflected reference beam. An appropriate selection of the polarization orientations of the interfering light beams leads to the suppression of one of the grating systems. Even to reconstruct TIR hologram it is not all the same in which orientation the reconstructing laser beam is polarized. With the proper selection of the polarization orientations of the forming and reconstructing laser light the diffraction efficiency for TIR holograms can be optimized.     

Dynamic holography in alkali metal vapour

Problems of dynamic hologram recording on resonant absorption lines of alkali metal vapour are discussed. Light beams and media parameters are determined that are necessary for hologram recording with usable efficiency. The effects of thermal atomic motion and the radiative transport of excitation influence on the spatial frequency transfer function of two-level media are investigated. Results of hologram recording in vapour of Rb (780.0 nm) and Cs (852.1 nm) using low-power CW-lasers are presented. Transmission holograms in the volume media and reflection holograms near the boundary of the resonant vapour and the dielectric are compared. For transmission holograms the advantage of collinear read-out when using pure vapour in comparison with a counterpropagating read-out is shown, and this makes it possible to achieve higher values of hologram efficiency over a wide range of atomic density. It is shown that reflection hologram recording is characterized by higher resolution, as compared with hologram recordings in the volume of extended media. Problems of metal vapour hologram usage for laser parameter control are discussed. The feasibility of holograms in Cs-vapour usage as a spectral-selective real-time feedback element in a semiconductor laser external cavity is shown.     

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.     

An Iterative Fourier Transform Algorithm for digital hologram generation using phase-only information and its implementation in a fixed-point digital signal processor

An Iterative Fourier Transform Algorithm (IFTA) for digital hologram generation from a digital image using phase-only information is described in this paper. The algorithm is implemented in a Texas Instruments TMS320C64x fixed point digital signal processor (DSP). The holograms are reconstructed in real time using a liquid crystal display system and a He–Ne laser. The ideas described in this paper can be extended to digital hologram generation of three-dimensional objects and their reconstruction in real time using liquid crystal spatial light modulators, which could be a way for 3D-display systems.     

Application of interference microscopy to the study of hologram build-up in LiNbO3 crystals

Interference microscopy was applied to direct microscopic observation of temporal evolution of phase holograms in LiNbO₃:Fe photorefractive crystals. First a hologram was recorded in the sample, and diffraction efficiency was monitored during hologram build-up using inactinic laser light. Thus kinetics of hologram build-up could be determined. The initial hologram was erased using white light. Then a series of write-erase cycles were performed with increasing exposure times. Holograms were observed by interference microscope after each exposure. The time elapsed between the exposure and the microscopic observation was negligible compared to the relaxation time of the hologram. The obtained temporal evolution of the grating profile gives a deeper insight into the physical mechanism of hologram formation in photorefractive materials than simple diffraction efficiency measurements. A congruently grown sample of LiNbO₃ doped with 10⁻³ mol/mol Fe in melting was studied by this method. Sample thickness was set to 300 μm to allow correct microscopic observation. Plane-wave holograms were recorded in the samples using an Ar-ion laser at λ = 488.0 nm of grating constants of 3, 6.5 and 8.8 μm.     

Application of Surface Relief Hologram Using Azobenzene Containing Polymer Film

Surface relief holograms are fabricated by irradiation of laser interference patterns on an azobenzene polymer film. The hologram needs no post-treatment, and can be erased by heating the films to above its glass transition temperature. Rewritable Fresnel holograms are fabricated on azo-polymer film. Replication of the surface relief hologram is also demonstrated. An application for business cards is considered.     

Incremental holographic recording in lithium niobate with active phase locking

Angular-multiplexed hologram recording in iron-doped lithium niobate crystals was carried out with near-infrared light. An incremental recording schedule with active phase locking of the light pattern onto the hologram was used. Continuous and reproducible recording of holograms of equal efficiency was achieved, and a hologram multiplexing number, M/#=2 , for a 5-mm-thick crystal was obtained at a 760-nm wavelength of light.     

全息立体多重像的拍摄

本文介绍了用光栅对参考光进行调制,从而拍得全息立体多重像的方法。     

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.     

Computer Generated Rainbow Hologram

The rainbow hologram is very practical to display 3-D images because it can be reconstructed with white light. We propose a simplified model to calculate the computer generated rainbow hologram quickly. In the proposed method, we can simply generate the final hologram from intermediate data, whose total number of samples can be less than one tenth of the final hologram. This intermediate format makes fast computation and effective storage/transmission possible. Only multiple and additional operation need be used to convert the intermediate data to final data. Therefore, it is possible that hardware can be added to an electro-holographic display or printer. In this paper, we discuss both theory of the simplified model and experimental results of white light reconstructed images. Full color holograms are also discussed.     

Angle-multiplexed hologram storage in LiNbO(3):Tb, Fe

We have performed hologram multiplexing with a cw laser at lambda=532 nm in a near-stoichiometric LiNbO(3) :Tb, Fe crystal that exhibits a visible absorption band induced by UV light. When 50 plane-wave holograms were angle multiplexed from the UV preexposed state, the recording sensitivity gradually decreased, owing to bleaching of the induced absorption. However, a conventional recording schedule of multiplexing many holograms of equal diffraction efficiency can be used in this photochromic material. The gradual decrease in recording sensitivity throughout multiplexing can be compensated for by the increased erasure-time constants of later-written holograms. An M/# of 1.73 was obtained in a crystal of 3.3-mm thickness.     

二维彩虹全息图母版的非相干光拷贝技术

描述一种用非干光制作二维彩虹模压全息图母版的新技术。该技术用紫外灯作为记录光不原,记录系统中不用任何光学元件。记录过程不需防振条件,色彩编码 狭缝像的“彩虹版”上进行条纹复制而获得。彩虹版可以无数次重复使用,所以全息图母版的记录十分简单。该技术投资少、效率高,制出的全息图质量好,对大批量模压全息图制造有很高的实用价值。     

Optical retrieval of encrypted digital holograms for secure real-time display

Secure data transmission by use of encrypted digital holograms and an optical retrieval system for secure real-time display are proposed. Original images are encrypted by a double-random phase encryption technique and then are recorded as digital holograms in a CCD, together with a reference plane wave. This digital hologram of the encrypted image can be transmitted to receivers via any conventional electronic or digital communication channels. The decryption key is also recorded as a digital hologram. At the receiver, the original image can be retrieved by an optical correlation-based reconstruction process. Both encryption and retrieval can be performed by all-optical means, and thus a real-time secure display can be implemented. We demonstrate the proposed system numerically and experimentally.     

Interferometric moiré pattern encoded security holograms with concealed phase object

This paper describes an interferometry-based scheme for concealing phase objects in a security hologram. The decoding process is based on geometrical moiré technique and requires a key for hologram authenticity verification. Decoding process is straightforward and could be carried out in white light, making it suitable for validation of security holograms. The method is described and experimental results are presented.     

Display method with compensation of the spatial frequency response of a liquid crystal spatial light modulator for holographic femtosecond laser processing

Liquid crystal spatial light modulators, which are widely used as display devices for computer-generated holograms, have modulation characteristics that depend on spatial frequency. We describe a method for displaying a computer-generated hologram on a liquid crystal spatial light modulator with compensation of its spatial frequency response. Using this method, we demonstrate a binary phase grating with smaller dependence on the spatial frequency. We also demonstrate application of the display method to holographic femtosecond laser processing.     

Imaging of rotating objects by means of synthesized optical holograms

A scheme is presented for producing optical holograms of rotating objects by illuminating the object by a single-frequency coherent laser beam. Along one axis, the synthesis takes place due to rotation of the object; along the other axis, the hologram is synthesized by the coherent radiation field generated by a long linear optical antenna. Numerical simulation shows that reliable discrimination of object images from the accompanying background is possible, for point objects, using a single hologram recorded at one angular position and, for extended flat objects or thin cylinder-like objects, using holograms recorded at two or three angular positions. If the holograms are synthesized in the presence of normally distributed random phase noise, the quality of the reconstructed images of rotating objects remains sufficiently high for root-mean-square noise amplitudes exceeding π/2 and reaching the limiting value 2π/3.