White Light Phase-conjugate Lensless Image Projection

Abstract

The lensless projection in white light of images with ～ 30 µ;m resolution has been demonstrated using phase-conjugate reflections from a self-pumped BaTiO₃ crystal which was simultaneously illuminated with red, green and blue laser light. The relative beam incident intensities were crucial in reducing holographic photoerasure and cross-talk effects.     

Rainbow holography of a diffuse three-dimensional object with a synthetic slit

Abstract

A study of rainbow holography with a movable synthetic slit in three-dimensional (3D) space is presented. A diffuse 3D object and an imaging lens are translated uniformly along the same direction with different (or identical) speeds in the X-Y plane. The spatial frequencies of the coherent wave illuminating the object are α, 0 and γ. As a result, the synthetic slit in rainbow holography is presented at a position which depends on the translational direction of the object and the imaging lens, their relative speeds, the spatial frequency of the illuminating wave in the X ₀ direction, and the relative distance of the reference source and the reconstruction source from the holographic plate. Theoretical analysis and some experimental results are presented.     

Analysis of slitless holographic spectrometers implemented by spherical beam volume holograms

The analysis of a slitless volume holographic spectrometer is presented in detail. The spectrometer is based on a spherical beam volume hologram followed by a Fourier-transforming lens and a CCD. It is shown that the spectrometer is not sensitive to the incident angle of the input beam for the practical range of applications. A holographic spectrometer based on the conventional implementation is also analyzed, and the results are used to compare the performance of the proposed method with the conventional one. The experimental results are consistent with the theoretical study. It is also shown that the slitless volume holographic spectrometer lumps three elements (the entrance slit, the collimator, and the diffractive element) of the conventional spectrometer into one spherical beam volume hologram. Based on the unique features of the slitless volume holographic spectrometer, we believe it is a good candidate for portable spectroscopy for environmental and biological applications.     

A Blazed Holographic Concave Grating for Monochromators

Abstract

The theory of blazed holographic gratings given in a previous paper is applied to the design of a blazed holographic aberration-corrected spherical concave grating. Two solution types are found which cover different ranges of blaze wavelength and aberration. The use of the refractive indices of the substrate, and the medium in front of the photoresist, as optimising parameters is demonstrated. Four ray-traced solution examples are given which include the distributions of blaze angle and wavelength across the grating surface.     

Color image generation of a three-dimensional object with rainbow holography and a one-wavelength laser

Based on conventional one-step true-color rainbow holography, a new true-color rainbow holography of a three-dimensional diffused object is presented. By means of conjugate reconstruction with a onewavelength laser of a master hologram recorded with three laser wavelengths, the hologram can be transferred to a single type of recording material with a single exposure to achieve true-color holographic display. Therefore a photoresist master can be produced for embossing copy.     

阿达玛变换成像光谱仪编码模板的设计与制作

编码模板是阿达玛变换成像光谱仪的关键部件，用以代替入射狭缝和出射狭缝。根据编码模板的构造原理，通过计算机生成二元伪随机序列码，用C语言根据编码方式生成图形文件，进而光刻出编码模板。应用该方法可制作任意形状和大小，特别是码元数目较大的编码模板，能实现高分辨率的编码。     

Polarization separation of light in holographic grating reflection in conical mounting

Abstract

We experimentally investigate the interaction of linearly polarized light with a holographic grating in a conical mounting. Due to the periodic structure, the polarization properties of the reflected zeroth-order beam are highly sensitive to the conical angle. When a focused Gaussian beam with linear polarization impinges on an air–grating interface at an exceptional conical angle, a spatial splitting of the reflected beam is observed behind a polarizer. We find that it can be interpreted using the anisotropy of the polarization distribution in holographic grating reflection.     

Novel optical photorefractive storage-retrieval system using speckle coding technique in beam-fanning geometry

Abstract

An encoding technique based on speckle random patterns as carrier together with the beam-fanning concept is introduced to realize photo-refractive optical volume holographic memory. The set-up is based on beam-fanning geometry employing a single input beam in a BaTiO₃ crystal. Retrieval of information from this kind of memory system is very sensitive to code matching. Therefore, in the case of multiple storage, the cross-talk is minimized. The preliminary experimental results are presented with their possible applications in increasing the information storage capacity of volume holographic memories, with resultant reduced cross-talk. A dual-channel optical processor has also been realized wherein object information together with its contrast reversed version are obtained at the output channels simultaneously.     

Multiple fractional fourier transform hologram by use of holographic lens

Abstract

A new method is presented to record multiple fractional Fourier transform holograms by use of a holographic lens. With holographic lenses, several fractional Fourier transform holograms of different objects can be recorded in a simple way, and images of these recorded objects can be reconstructed in different positions and directions in three-dimensional space. In this paper, the theory and characteristics of the hologram recorded using the holographic lens are analysed. Using this method, a multiple fractional Fourier transform hologram was fabricated, with satisfactory results.     

Simultaneous determination of the refractive index and wedge angle of an optical wedge plate using a photorefractive holographic interferometer

Abstract

A simple and effective method for simultaneously determining the refractive index and the wedge angle of an optical wedge plate is described. The method is based on a real-time holographic interferometer which uses a photorefractive crystal as the recording and reconstruction medium. The wedge sample under test is inserted into a rectangular cell that is placed in the object light beam of the holographic interferometer. The interference patterns produced before and after a reference liquid is poured into the cell are received by a CCD camera and stored in a computer, respectively. The refractive index and the wedge angle of the wedge sample are determined by measuring the number of fringes falling inside a fixed aperture. The principle of the method is analysed and some experimental results with adequate accuracy are given.     

Holographic Noise Gratings for Analysing and Optimizing Photochemical Processings in Bleached Silver Halide Emulsions

Abstract

Recording noise gratings with single-beam exposures in bleached silver halide emulsions is used as a holographic spectroscopy technique in order to analyse and optimize photochemical processing. In particular, rehalogenating type bleachings are analysed by measuring the transmittance through the recorded and processed holographic plate as a function of the reconstruction angle, the exposure and the concentration of the rehalogenating agent in the bleach bath. The experimental results obtained show us that the analysis of these spurious gratings provides information about the bleaching action during the processing and allows us to identify the optimal concentration of the bleach bath.     

Influence of beam polarisation in laser bending process

Abstract

In this paper, the influence of beam polarisation in the laser bending process was experimentally studied. Based on the laser beam polarisation, the laser absorption of the metallic specimen could be enhanced by increasing the incident angle. The bending angles are achieved in stainless foil specimens without absorptive coatings, and larger bending angles can be produced by single laser scanning with higher incident angles. Multipass laser bending experiments were also carried out on the same material with graphite coatings. The results show that the bending angle per pass is affected obviously by the beam polarisation at lower laser line energy; and the bending angle per pass increases significantly when the total bending angle is large enough. When using polarised light, the laser beam distortion and laser absorption change induced by the variation of the absorptive coatings and laser incident angle are the two main factors that affect the coupled laser energy. The bending rule is the synthesis effect of the two factors.     

Exterior caustics produced in scattering of a diagonally incident plane wave by a circular cylinder: semiclassical scattering theory analysis

We use the semiclassical limit of electromagnetic wave scattering theory to determine the properties of the exterior caustics of a diagonally incident plane wave scattered by an infinitely long homogeneous dielectric circular cylinder in both the near zone and the far zone. The transmission caustic has an exterior/interior cusp transition as the tilt angle of the incident beam is increased, and each of the rainbow caustics has a farzone rainbow/exterior cusp transition and an exterior/interior cusp transition as the incident beam tilt angle is increased. We experimentally observe and analyze both transitions of the first-order rainbow. We also compare the predictions of the semiclassical approximation with those of ray theory and exact electromagnetic wave scattering theory.     

Beam focusing and unidirectional excitation from four nanoslits filled with air and non-linear material

Abstract

We theoretically design a device composed of four nanoslits to dynamically modulate the propagation direction of light beam by embedding non-linear material and air, respectively. Directions of radiation fields are determined by the phase difference of the surface waves at the exit interface and distance of each slit. Numerical simulations using finite element method verify that the unidirectional excitation and beam focusing can be achieved easily by changing the intensity of incident light.     

Electric polarization and the extinction of the extraordinary reflected ray

Abstract

When light is incident from an isotropic medium on to an interface with a uniaxial crystal, the idea of an effective electric polarization is useful. We show that the same idea may be extended to the reverse situation where the light is incident from the uniaxial crystal. In this case, when the optical axis lies in the plane of incidence, there is a Brewster angle associated with the extinction of the reflected ray, because the waves have a definite polarization. We analyse the relation between the Brewster angle and the effective electric polarization at the interface.     

Rainbow holographic aberrations and the bandwidth requirements

Rainbow holographic image resolution, primary aberrations, and bandwidth requirements are presented. The results obtained for the rainbow holographic process are rather general, for which the conventional holographic image resolution, aberrations, and bandwidth requirements, can be derived. The conditions for the elimination of the five primary rainbow holographic aberrations are also given. These conditions may be useful for the application of obtaining a high-quality rainbow hologram image. In terms of bandwidth requirements, we have shown that the bandwidth requirement for a rainbow holographic construction is usually several orders lower than that of a conventional holographic process. Therefore, a lower-resolution recording medium can generally be used for most of the rainbow holographic constructions.     

Single-channel color image encryption using a modified Gerchberg-Saxton algorithm and mutual encoding in the Fresnel domain

A single-channel color image encryption is proposed based on the modified Gerchberg-Saxton algorithm (MGSA) and mutual encoding in the Fresnel domain. Similar to the double random phase encoding (DRPE), this encryption scheme also employs a pair of phase-only functions (POFs) as encryption keys. But the two POFs are generated by the use of the MGSA rather than a random function generator. In the encryption process, only one color component is needed to be encrypted when these POFs are mutually served as the second encryption keys. As a result, a more compact and simple color encryption system based on one-time-pad, enabling only one gray cipheretext to be recorded and transmitted when holographic recording is used, is obtained. Moreover, the optical setup is lensless, thus easy to be implemented and the system parameters and wavelength can be served as additional keys to further enhance the security of the system. The feasibility and effectiveness of the proposed method are demonstrated by numerical results.     

Lensless anamorphic Fourier transform hologram recorded with prism systems

A novel configuration for recording a lensless anamorphic Fourier transform hologram of a given object's light distribution is proposed. The method is based on the use of prism anamorphic optical systems coupled with phase cancellation at the hologram plane. Anamorphic systems with cylindrical lenses and prisms are critically evaluated through computer simulations for their suitability in anamorphic Fourier transform holographic configurations. A complete theoretical analysis and experimental demonstration of the recording and reconstruction of a lensless anamorphic Fourier transform hologram are presented.     

The self-imaging effect in lensless holographic microscopy and its application in characterising periodic structures

A lensless holographic microscope was used to record a hologram of self-organised monolayers of micron-sized polystyrene spheres. By reconstructing the hologram digitally using a computer it was found that the original periodicity of the object produces planes of identical images, as well as planes that show reversed contrast images at separations predicted by the first-order approximation to the Talbot theory of the self-imaging effect. The performance of a compound light microscope is compared and contrasted with that of the holographic system, specifically examining the ability of the different systems to recover the distribution at the Talbot planes and to characterise properties of periodic structures. A theoretical model is developed and experimental results are presented.     

Numerical Analysis of the Near-field Diffraction Pattern of a Small Aperture

Abstract

We show the three-dimensional (3-D) distribution of the time-averaged Poynting vector in the near-field of a small aperture (radius < λ) using Bethe's diffraction theory. Our numerical calculation shows that the characteristic of the near-field diffraction depends on the incident angle of the beam on the aperture. Specifically, the near-field diffraction corresponding to the normal incident has a quite different character than that of the oblique incident. We also discuss the variation of the propagation of the time-averaged Poynting vector with the aperture size, the wavelength and the distance from the aperture.