Holographic optical elements recorded in silver halide sensitized gelatin emulsions. Part 2. Reflection holographic optical elements

Silver halide sensitized gelatin (SHSG) holograms are similar to holograms recorded in dichromated gelatin (DCG), the main recording material for holographic optical elements (HOEs). The drawback of DCG is its low energetic sensitivity and limited spectral response. Silver halide materials can be processed in such away that the final hologram will have properties like a DCG hologram. Recently this technique has become more interesting since the introduction of new ultra-fine-grain silver halide (AgHal) emulsions. In particular, high spatial-frequency fringes associated with HOEs of the reflection type are difficult to construct when SHSG processing methods are employed. Therefore an optimized processing technique for reflection HOEs recorded in the new AgHal materials is introduced. Diffraction efficiencies over 90% can be obtained repeatably for reflection diffraction gratings. Understanding the importance of a selective hardening process has made it possible to obtain results similar to conventional DCG processing. The main advantage of the SHSG process is that high-sensitivity recording can be performed with laser wavelengths anywhere within the visible spectrum. This simplifies the manufacturing of high-quality, large-format HOEs, also including high-quality display holograms of the reflection type in both monochrome and full color.     

Holographic optical elements recorded in silver halide sensitized gelatin emulsions. Part I. Transmission holographic optical elements

Silver halide sensitized gelatin (SHSG) holograms are similar to holograms recorded in dichromated gelatin (DCG), the main recording material for holographic optical elements (HOE's). The drawback of DCG is its low sensitivity and limited spectral response. Silver halide materials can be processed in such a way that the final hologram will have properties like a DCG hologram. Recently this technique has become more interesting since the introduction of new ultra-high-resolution silver halide emulsions. An optimized processing technique for transmission HOE's recorded in these materials is introduced. Diffraction efficiencies over 90% can be obtained for transmissive diffraction gratings. Understanding the importance of the selective hardening process has made it possible to obtain results similar to conventional DCG processing. The main advantage of the SHSG process is that high-sensitivity recording can be performed with laser wavelengths anywhere within the visible spectrum. This simplifies the manufacturing of high-quality, large-format HOE's.     

DCG全息研究进展

对重铬酸盐明胶全息的发展历史，成像机理，明胶对全息性能的影响，ＤＣＧ的增感和全息图的稳定性等作了全面综述，并对ＤＣＧ的性能改善了作了展望。     

Recording selectograms in thick dichromated gelatin

The results of experiments with holographic imaging by means of reference-free selectograms recorded in thick layers of self-developing glycerol-containing dichromated gelatin (DCG) are presented. The contrast of the reconstructed image is characterized as a function of the spatial frequency.     

Hologram formation in dichromated gelatin: an approach based on light scattering from nanoparticles

Dichromated gelatin is one of the best materials for phase-hologram recording. Several competing hypotheses for the nature of the photoinduced response in DCG have been discussed in the literature. Of particular interest is the assumption that processing of the latent image leads to the formation of voids in the gelatin matrix. Here, we analyze the DCG hologram performance in terms of the theory of light scattering from these voids – ellipsoids with dimensions of 10–40 nm. Mathematical simulations of the reflection spectra give a plausible quantitative explanation of many experimental facts related to DCG holograms.     

Improving the holographic sensitivity of dichromated gelatin in the blue-green part of the spectrum by sensitization with xanthene dyes

The holographic properties of dichromated gelatin (DCG) sensitized with various xanthene dyes were studied, and results are reported. The sensitivity of dyed DCG in the green part of the spectrum compared with that of pure DCG (215 mJ/cm(2)) was significantly improved by addition of Rhodamine 6G (140 mJ/cm(2)) or Erythrosin B (90 mJ/cm(2)). Diffraction gratings were recorded with a He-Ne laser at 543.5 nm. The maximum diffraction efficiency was found to be 32% at normal incidence of the readout beam; it was 80% at the Bragg angle.     

Observation of a fast-formed absorption grating and a slowly formed phase grating in undeveloped dichromated gelatin

Real-time diffraction efficiency is measured during hologram formation in undeveloped dichromated gelatin (DCG) film. The main features of real-time diffraction efficiency of undeveloped DCG reveal double peaks with increasing exposure time. Adopting the grating translation technique, we show that the first peak originates from the absorption grating and that the latter is related to the phase grating. To explain such complicated hologram-formation dynamics, we present a phenomenological model for mixed gratings associated with photoinduced refractive-index changes and absorption changes. We have compared the model results with the experimental results, which show good agreement.     

Comparison of methods for determining the bias index of a dichromated gelatin hologram

Determination of the bias refractive index of a holographic emulsion before exposure and after development is an important factor in the design of holographic optical elements. Several experimental methods are discussed for determining the bias index of a volume hologram in dichromated gelatin, and the results for each technique are presented. It is shown experimentally that these measurement methods yield different results for the same hologram, and the cause of the differences is proposed to be a variation of the bias index with depth in the hologram. An index measurement technique is also presented that accounts for variation in the bias index and is shown to yield an accurate value for the bias index.     

Silver-halide sensitized gelatin derived from Agfa-Gevaert holographic plates

To our knowledge only one processing formula for silver-halide sensitized gelatin (SHSG) derived from Agfa-Gevaert holographic plates has been published in the current literature, which is apparently a result of the extremely high degree of hardening of the gelatin emulsion. We propose a modified processing formula for SHSG derived from Agfa-Gevaert plates. The holographic characteristics of the processed SHSG plates were measured and high diffraction efficiency, as high as 80%, and an almost flat spatial-frequency response within the region of interest were achieved. Some of our observations during the experiments are discussed. The behavior of the gelatin emulsion was consistent with the models for processing dichromated gelatin. We observed swelling rather than the shrinkage expected from the removal of the silver-halide grains. This swelling can be controlled by postbaking.     

全息照相及常用的全息记录材料

本文简要概述了全息照相的概念、白光显示全息图及其应用状况。全息照相是一种新型的照相技术,与普通照相相比较具有三维立体性、重复记录性、可分割性等优点。本文还介绍了用于全息照相的记录材料,主要有三种:卤化银全息干版、DCG干版和高分子感光材料。     

The phenomenon of light concentration by a speckle screen based on a reference-free volume hologram

It is experimentally demonstrated that a speckle screen based on a reference-free volume hologram is capable of concentrating light in the visibility zone. Holographic speckle screens for the projection of images were formed in a bulk photosensitive material based on glycerol-containing dichromated gelatin (DCG). With such screens formed using radiation with a wavelength (0.442 nm) in the spectral range of DCG photosensitivity, it is possible to obtain high-quality image projections using both coherent radiation with a different wavelength and white light. The projection properties of speckle screens were studied, and their ability to concentrate light in the visibility zone was confirmed.     

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.     

Secondary Holograms in Dichromated Gelatin Filters

Reflective volume gratings in dichromated gelatin film have been studied under conditions in which secondary holograms are produced, where, during exposure, the holographic film is placed in optical contact with a prism. Optimum reconstruction angles and diffraction efficiencies are determined for the secondary holograms that are recorded as a result of internal reflection.     

Holographic parabolic mirror as a receiver optical front end for wireless infrared communications: experimental study

The inherent multifunctionality of holographic optical elements and their light physical weight make them an attractive solution for the receiver optics of portable terminals in indoor infrared wireless communication systems. A parabolic holographic mirror has been recorded in silver halide at a visible wavelength, and its replay wavelength has been shifted to the near infrared. Employment of proprietary swelling technology resulted in a permanent replay wavelength shift without the need for hologram sealing. Despite the relatively low diffraction efficiency of holograms recorded in silver halide in principle, an improvement in the receiver signal-to-noise ratio of more than 20 dB has been measured. The results of the conducted experiments proved undoubtedly the great potential of curved holographic mirrors as a key element of the receiver optical front end in IR wireless communication systems.     

Self-enhancement of holographic gratings in dichromated gelatin and polyvinyl alcohol films

New experimental results concerning real-time hologram recording in dichromated sensitized gelatin and polyvinyl alcohol are presented. Self-enhancement of the holographic gratings observed in the dark in both of these dye-polymer systems is shown.     

曝光量对DCG中Cr2P_(3/2)XPS谱的影响的研究

通过对不同曝光量的重铬酸盐明胶(DCG)中的Cr2P3／2XPS（X射线光电子能谱）的规定发现，Cr2P3／2XPS谱随曝光量呈规律性的变化：在0～195mJ／cm2曝光量范围内，它的1／5高宽度（FWFM，即：thefullwidthatfifthmaximum）和576．4eV附近的峰的相对强度先随曝光量增加而增大，到达极大值后又随曝光量的增加而减小；相反，它的579．4eV和577．4eV附近的两个峰的相时强度却是先随曝光量的增加而减小，达到极小值后又随曝光量的增加而增大。对这些不同曝光量的DCG膜定性地水洗处理后，曝光量为130mJ/cm2的全息图最均匀、明亮；曝光量为195mJ／cm2的全息图衍射效率很低，且有残余黄褐色。根据这些实验结果和固态膜反应的特点，就曝先对DCG微观结构引起的变化作了分析，确定出了贡献各峰的化合物状态并科学准确地找到了Cr2P3／2XPS谱随曝光量成规律性变化的本质原因是作为潜影中心的二氧化铬（576．4eV附近的铬）严格地受曝光量的制约。这个结论的得出，为制作理想的全息图选择合适的曝光量提供了理论依据。即：576．4eV附近的峰有最大相对强度的曝光量为最佳曝光量。     

Spherical beam volume holograms for spectroscopic applications: modeling and implementation

The spherical beam volume hologram, recorded by a plane wave and a spherical beam, is investigated for spectroscopic applications in detail. It is shown that both the diffracted and the transmitted beam can be used for spectroscopy when the hologram is read with a collimated beam. A new method is introduced and used for analysis of the spherical beam volume hologram that can be extended for analysis of arbitrary holograms. Experimental results are consistent with the theoretical study. It is shown that the spherical beam volume hologram can be used in a compact spectroscopic configuration when the transmitted beam is monitored. Also, on the basis of the properties of the spherical beam hologram, the response of a hologram recorded by a plane wave and an arbitrary pattern is predicted. The information can be used to optimize holographic spectrometer design.     

Digital color management in full-color holographic three-dimensional printer

We propose a new method of color management for a full-color holographic, three-dimensional (3D) printer, which produces a volume reflection holographic stereogram using red, green, and blue three-color lasers. For natural color management in the holographic 3D printer, we characterize its color reproduction characteristics based on the spectral measurement of reproduced light. Then the color conversion formula, which comprises a one-dimensional lookup table and a 3×3 matrix, was derived from the measurement data. The color reproducibility was evaluated by printing a color chart hologram, and the average CIELAB ΔE=13.19 is fairly small.     

Reflection volume holographic scanners with field-curvature corrections

A new type of polygonal holographic scanner that combines a reflection volume hologram with a computer-generated hologram (CGH) is described. The scanner is free from the aberration of field curvature. Such a scanning system can allow for a compact folded version of the scanner and Bragg diffraction into only a single order. The equations expressing the spatial-variable image distance are derived and are fit to the phase function designated by polynomials incorporated into a CGH in terms of the least-squares method. A reflection scanner with field-curvature correction is made by interfering a diffracted wave front from this CGH with a spherical wave front having scanning focal power through a second plane hologram. Experiments demonstrating the feasibility of this scanner are presented. Raster-scan patterns using a multifaceted scanner are shown. Helpful data on the diffraction efficiency and the spectrally diffracted intensity of reflection holograms are also presented.     

Hybrid process of latent image formation in silver halide sensitized gelatin: differential hardening with microvoids

Renewed interest has been shown in the hybrid silver halide sensitized gelatin processes owing to the appearance of new photographic materials. In this study we show the possible compatibility between the models of latent image formation proposed prior to the existence of these new materials, bearing in mind that the refractive-index modulation and its curve of spectral response should be the figures of merit for optimization of the processes of transmission and reflection hologram formation.