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.     

Holographic diffuser by use of a silver halide sensitized gelatin process

Diffusers play an important role in liquid crystal display (LCD) application as a beam-shaping device, a brightness homogenizer, a light-Scattering device, and an imaging screen. The transmittance and diffusing angle of the diffusers are the critical aspects for the applications to the LCD. The holographic diffusers by use of various processing methods have been investigated. The diffusing characteristics of different diffusing materials and processing methods have been evaluated and compared. The microstructures of holographic diffuse have been investigated by use of using scanning electron microscopy. The holographic diffusers by use of the silver halide sensitized gelatin (SHSG) method have the structural merits for the improvement of the quality of diffusers. The features of holographic diffuser were exceptional in terms of transmittance and diffusing angle. The replication method by use of the SHSG process can be directly used for the manufacturing of diffusers for the display application.     

Silver halide sensitized gelatin process effects in holographic lenses recorded on Slavich PFG-01 plates

In this work we study the feasibility of using silver halide sensitized gelatin based on PFG-01 (Slavich) emulsions to construct uniaxial compound lenses. This processing is able to introduce variations in the thickness and refractive index of the emulsion. We prove that these changes are not sufficient to provide the observed variations in Bragg conditions in the reconstruction and that a shear-type effect must exist to explain the performance of processed emulsions. We study the characteristics of a compound lens, obtaining acceptable image quality, good resolution, and the typical field limitation of volume holographic elements.     

Silver halide sensitized gelatin derived from BB-640 holographic emulsion

Silver halide sensitized gelatin (SHSG) is one of the most interesting techniques for the production of holographic optical elements, achieving relatively high sensitivity of photographic material with a low scattering of dichromated gelatin. Here we present experimental results for SHSG derived from the novel BB-640, a red-sensitive ultra-fine-grain emulsion from Holographic Recording Technologies (Steinau, Germany). The material is characterized before recording and after processing, and information about the thickness, absorption, and refractive-index modulation of the final holograms is obtained. The influence of the developer is analyzed, and diffraction efficiencies as great as 96.2% (after allowing for reflections) with a transmission of 1% and absorption and scatter losses of 2.8% are obtained with AAC developer. Our investigations reveal that high-quality SHSG transmission holograms may be obtained with the new BB-640 plates.     

Holographic optical elements recorded on spherical surfaces with photopolymers

A method for recording of holograms on spherical substrates is presented. As recording material we used a photopolymer placed between two spherical glass plates that are concentric.     

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.     

Silver halide sensitized gelatin holograms in Slavich PFG-01 red-sensitive emulsion

Abstract

Silver halide sensitized gelatin (SHSG) is an interesting technique for the production of holographic optical elements. It combines the high sensitivity of photographic emulsions with the well-known low scattering and high diffraction efficiency corresponding to dichromated gelatin. In this paper we describe SHSG holograms recorded on Slavich PFG-01 emulsions. We will show that real high diffraction efficiencies can be obtained (as high as 93% allowing for reflections) when using this material for recording phase transmission holograms. The influence of the bleach bath temperature and a hardening bath in the processing was studied and the procedure was optimized for these two parameters. Our investigations reveal that PFG-01 emulsion is not only a substitute for Agfa material, but also offers better results, at a moment in which Agfa has stopped its production of holographic material.     

Reflection and transmission properties of holographic mirrors and holographic Fabry-Perot filters. Ill. Holographic Fabry-Perot filters

The reflection and transmission coefficients of holographic Fabry-Perot filters (HFPF's) are derived. Angular selectivities and wavelength sensitivities of the HFPF's on transmitted light are investigated. The effects of transmission by a HFPF on the spectrum and on the coherence properties of a partially coherent incident light are also analyzed. Numerical examples are presented for the case in which the incident light is generated by a Gaussian Schell-model source.     

Reflection and transmission properties of holographic mirrors and holographic Fabry-Perot filters. I. Holographic mirrors with monochromatic light

The reflection and transmission coefficients of holographic mirrors (HM's) and holographic Fabry-Perot filters (HFPF's) are studied. The diffraction efficiencies, the angular selectivities, and the wavelength sensitivities of HM's and HFPF's and their effects on the spectrum and on the coherence properties of the incident light are investigated. The results show that holographic techniques can indeed be used to construct high-quality reflecting mirrors and Fabry-Perot filters. HM's illuminated by a monochromatic plane wave are investigated in detail. The reflection and transmission coefficients are first studied as functions of frequency (wavelength) of the incident light and also as functions of the angle of incidence. It is shown that HM's can be used as highly reflecting mirrors around their Bragg angle of incidences. Their reflectivity curves have fairly wide angular- and frequency-selectivity ranges.     

Reflection and transmission properties of holographic mirrors and holographic Fabry-Perot filters. II. Holographic mirrors with partially coherent light

The reflection and transmission properties of holographic mirrors (HM's) under partially coherent illumination are investigated with emphasis on the properties of reflected light. The effects of a HM on the spectrum and on the coherence properties of partially coherent incident light are studied. We show that within angular and frequency-selectivity ranges of HM's (where their reflectivities are nearly uniform), the changes in the spectrum and in the coherence properties are negligible. Yet changes are expected when the spectrum of the incident light falls beyond frequency-selectivity ranges of the HM's or when the spectrum of the reflected light is observed beyond the angular-selectivity ranges of the mirrors. We illustrate the results by considering in detail the performance of HM's when the incident light is produced by planar secondary Gaussian Schell-model sources. Some computed curves are presented.     

Diffuse-object holograms in silver halide emulsions: influence of the beam ratio on the efficiency and the signal-to-noise ratio

The influence of the beam ratio between reference and object beam intensities on the characteristics of diffuse-object holograms recorded as volume phase holograms in bleached silver halide emulsion is experimentally analyzed. Measurements of the diffraction efficiency and the signal-to-noise ratio of the holograms are taken. The experimental results presented show that when the beam ratio increases, the diffraction efficiency decreases and the signal-to-noise ratio increases; these two holographic parameters behave in this way no matter what type of processing is used.     

Speckle suppression in holographic projection displays using temporal integration of speckle images from diffractive optical elements

Speckles on images in holographic projection displays (HPDs) were efficiently suppressed by the temporal sum of two diffractive images generated from diffractive optical elements (DOEs). Using a modified iterative Fourier transform algorithm, we obtained pairs of phase-only DOEs that generated the diffractive images with high negative correlation coefficients of -0.827 and -0.490 in the one-dimensional and the two-dimensional simulations, respectively. The suppression ratios of the speckles in the two simulations were 0.301 and 0.457, which were 61% and 35% lower, respectively, than the sum of the two uncorrelated images. We have successfully demonstrated that the sum of two negatively correlated images from DOEs can effectively reduce the image speckles and improve the image quality in HPD systems.     

Near-IR absorption in high-purity photothermorefractive glass and holographic optical elements: measurement and application for high-energy lasers

Volume Bragg gratings (VBGs) in photothermorefractive (PTR) glass are widely used for laser beam control including high-power laser systems. Among them, spectral beam combining based on VBGs is one of the most promising. Achieving 100+ kW of combined laser beams requires the development of PTR glass and VBGs with an extremely low absorption coefficient and therefore methods of its measurement. This paper describes the calorimetric method that was developed for measuring a low absorption coefficient in PTR glass and VBGs. It is based on transmission monitoring of the intrinsic Fabry-Perot interferometer produced by the plane-parallel surfaces of the measured optical elements when heated by high-power laser radiation. An absorption coefficient at 1085 nm as low as 5×10(-5) cm(-1) is demonstrated in pristine PTR glass while an absorption coefficient as low as 1×10(-4) cm(-1) is measured in high-efficiency reflecting Bragg gratings with highest purity. The actual level of absorption in PTR glass allows laser beam control at the 10 kW level, while the 100 kW level would require active cooling and/or decreasing the absorption in PTR Bragg gratings to a value similar to that in virgin PTR glass.     

Holographic optical elements in the presence of spherical aberration and focus error: Some remarks on imaging quality

Abstract

When aberrations are small, it is possible to use wave aberration variance to obtain the position of the best image plane in both conventional and holographic optical systems. However, when aberrations increase, this measurement is not sufficient and it does not provide the correct plane position for the best image. In this paper, two alternative methods for evaluating image quality in spherically aberrated on-axis holographic lenses are compared. These two methods are the standard deviation of the distribution of light intensity and entropy. Both methods are based on the calculation of the diffraction integral and the subsequent analysis of the distribution of light intensity as a probability density function for each image plane being analysed. Even though the results obtained with both methods are identical when aberrations are small, only entropy provides the best image when the value of these aberrations increases.     

Phase transitions in elements and compounds. Part 3

There is shown to be good agreement for certain systems between the optical and thermodynamic parameters characterizing collective phenomena: laser emission and phase transition.Translated from Izhenerno-Fizicheskli Zhurnal, Vol. 50, No. 6, pp. 1005–1007, June, 1986.