Exposure and Spectral Characteristics of Bulgarian Silver-halide Materials for Multicolor Holographic Recording

V. Sainov
DIT, Dublin, Ireland
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V. Sainov, E. Stoykova, B. Ivanov, M. Chakrapani, V.Toal, T. Petrova
Central Laboratory of Optical Storage and Processing of Information to Bulgarian Academy of Sciences and Centre for Industrial and Engineering Optics (IEO), DIT, Dublin, Ireland

The presented work summarizes the recently obtained results in development of ultra-fine grain panchromatic silver-halide emulsion for recording of RGB reflection holograms. The average grain size of the emulsion is about 10 nm which ensures its high resolution, diffraction efficiency and signal-to-noise ratio in a large dynamic range. For the needs of multicolor recording we used two suitable sensitizers for the red (maximum absorption at 632.8 nm) and for the green (maximum absorption at 532 nm) spectral regions; we relied on natural sensitivity of emulsion for recording in blue (400-442 nm). First, we studied exposure dependence of diffraction efficiency in successive RGB recording on a single plate starting from the shortest to the longest wavelength and vice versa. Second, simultaneous recording was realized at two wavelengths:red and green and green and blue. Chemical processing of the exposed plates included three steps: i) development with SM6 to form amplitude modulation of holographic recording; ii) bleaching by Slavich PBU-Amidol composition; iii) swelling of holograms with a water solution of collagen-hydrolysate to satisfy Bragg condition for reconstruction with the wavelengths of recording. To have a satisfactory output from the last step we made spectral measurement at illumination with white light at the angle of recording at different exposures and concentrations of the swelling solution. We obtained with a good repeatability that the Bragg condition for reconstruction in the case of simultaneous red and green recording is achieved at the same concentration of the swelling agent whereas for the deep blue (442 nm) recording this concentration is almost twice higher. This was the reason to implement the so called “sandwich” structure consisting of two single plates – one for blue recording and the other-for red and green. Thus we obtained high values of diffraction efficiency of the resulting hologram with a satisfactory color mixing. In addition, a LED light source with controllable intensity of emission in red, green and blue spectral regions was applied to study improvement of the color balance in reconstruction of reflection (Denisyuk type) holograms.