We present the results obtained using two different types of the new panchromatic ultra-fine grain emulsion BBVPan, manufactured by Colourholographics Ltd. The first emulsion type was manufactured by mixing three monochromatic precipitates, so that each silver halide grain is sensitised with one dye only. The second emulsion was obtained by making one single precipitate containing all three dyes mixed together, so that each silver halide grain may be sensitised by the three dyes. Both emulsions have been compared in order to produce multiple band holographic reflection gratings, multiplexed on a single layer of material. Three different laser systems were used: He-Cd (442 nm), frequency-doubled Nd-YAG (532 nm) and He-Ne (632.8 nm). High diffraction efficiencies, of over 52\%, were obtained for each of the three bands, with little wavelength shifting. Tests with diffuse objects have been also carried out, studying colour balance for each of the emulsions.
In this paper we have studied the recording of Fourier holograms in a PVA-AA photopolymer, analysing the influence of beam ratio in the quality of the reconstructed images. As a result, it has been observed that the variation of the beam ratio produces significant changes in the response of the material, showing that there is a range of optimal values that gives the best performance of the photopolymer for the recording of Fourier holograms. Effects on edge enhancement as consequence of spatial filtering on the reconstruction stage has been observed for low values of beam ratio. The best beam ratio obtained from this study has been used for holographic multiplexing of four Fourier holograms.
In recent years the interest shown in dry photopolymer films as holographic recording materials have increased dramatically. The main reasons for this are the special properties of these media, such as high diffraction efficiency, low noise, real-time processing and low cost. Moreover, these materials are an important option for displays, high density data storage, micro-optical elements and other information processing applications. In these materials the hologram formation mechanism has been broadly studied, and it has been proposed that the temporal behavior of the diffracted beams depends mainly on the diffusion processes. Thus, the spatial modulation of the refractive index and its evolution over time is the result of non-uniform polymerization and the diffusion of monomers. In this work an analysis of the proposed models and the effect of the diffusion coefficient on the behavior of polyvinylalcohol-acrylamide-based compositions is realized.
Holographic techniques have been used for manufacturing multiple band one-dimensional, two-dimensional, and three-dimensional photonic crystals with different configurations, by multiplexing reflection and transmission setups on a single layer of holographic material. The recording material used for storage is an ultra fine grain silver halide emulsion, with an average grain size around 20 nm. The results are a set of photonic crystals with the one-dimensional, two-dimensional, and three-dimensional index modulation structure consisting of silver halide particles embedded in the gelatin layer of the emulsion. The characterisation of the fabricated photonic crystals by measuring their transmission band structures has been done and compared with theoretical calculations.
In this work we have studied the characteristics of reflection gratings recorded with BB640 emulsions from Colourholographics Ltd. processed with a set of different developers and bleaching techniques. Overall diffraction efficiencies evaluated with spectral response curves result in values higher than 70% (80% taking into account reflection losses) for conventional fixation free rehalogenating bleaching processes, with very low scattering.
A slightly lower value was obtained with reversal bleaching techniques, but with lower scattering in the recordings.
For the latter, an analytical analysis of the spectral responses based on the Kogelnik's theory has been performed, leading to anomalous results regarding physical thickness of the hologram and the reply wavelength, a performance that points towards holographic profile distortions. We have also used a completely different processing scheme based on Kodak D8, a developer never used in reflection holography, with a direct bleach rendering 40% diffraction efficiency, a broad bandwidth and a reconstruction wavelength longer than the recording one.
Ion this work we present a distortion of the usual H-D curve due to the action of a high contrast developer, Kodak D8 on ultra fine grain emulsion. This effect has been found for emulsions BB640, with a mean grain size of 20 nm. This anomalous curve shows two different linear zones for two different exposure ranges and no solarization region. Densities higher than 11 have been measured. Superaditivity effects of D8 with different developing agents were studied. Based on obtained result with different holographic bleaching processes, some ideas on the mechanisms involved in the anomaly have been proposed.
Evaluation of the mechanical properties of films of the materials currently employed for recording diffractive optical elements is very important in order to foresee their mechanical behavior during the photochemical processing following recording of the interference pattern. This will also provide information about the mechanical and thermal stability of holograms recorded on these materials, which may be tested in the different environments in which the final application of the optical elements will be used. For quantitative evaluation of these properties in an acrylamide based photopolymeric system, a study was carried out on layers of films of polyvinylalcohol and polyvinylalcohol mixed with triethanolamine. Layers coated on glass substrate were subjected to both a high vacuum and temperature changes. Real time measurements of optical path variations in the film were performed using a vacuum interferometric measurement system.
Two novel holographic recording media based on silica gel methyl methacrylate (MMA) and hydroxy ethyl methacrylate (HEMA) organically modified ceramics (ORMOCERS) are presented and its holographic properties, inferred from the experimental data, are discussed. The recording of holographic gratings of both low-spatial frequency (50 lp/mm) and high-spatial frequency (1400 lp/mm) in a bulk ORMOCER matrix is reported. The gratings were recorded by UV irradiation-induced photopolymerization of the MMA or HEMA monomers embedded in the silica matrix. The Bragg gratings were successfully recorded by interference of two coherent beams of 351.1 nm wavelength. A linearly polarized He-Ne laser beam (632.8 nm) was used for continuous monitoring of the recording process by measurement of the diffraction efficiency and for enhancement of the grating creation process. High diffraction efficiencies (93%) and low absorption and scattering coefficients were measured during the holographic reconstruction by He-Ne laser beam. The most important holographic parameters of the gratings were inferred from the experimental data: diffraction efficiency, angular selectivity, refraction-index modulation amplitude, spectral sensitivity, the Klein-Cook parameter, and the environmental stability of the gratings.
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