New recording material with AgBr nanoparticles for optical holography

Milan Kveton
Czech Technical University in Prague, Czech Republic

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A new recording material with silver halide (AgBr) nanoparticles and photopolymerization system will be presented. It is well known that redistribution of silver halide particles within a gelatin layer is the main cause of a phase hologram formation in silver halide emulsions (SHE). Holograms recorded in SHE reach high value of the refractive index modulation as the difference between refractive indexes of AgBr and gelatin is relatively high. However, the AgBr nanoparticles in SHE may increase in their size during the wet chemical developing and rehalogenization processes. So when the SHE hologram is reconstructed, it appears noisy as the size of scattering particles grew up.

Recently, we have developed a new self-developing recording medium with AgBr nanoparticles. It is composed of the gelatin binder with AgBr nanoparticles to which a photopolymerization system is added. During the holographic exposure, the radical chain polymerization process is initiated in the bright regions and polymer chains grow. As a consequence of the local polymerization process, the nanoparticles are excluded from polymerization regions and migrate to the surroundings where the local refractive index is growing up. The final result of nanoparticles distribution is the same as in the case of the processed SHE, but the AgBr nanoparticles in the gelatin layer preserve their original size as they don not undergo any chemical reactions.

In our laboratory, the AgBr nanoparticles in gelatin sol are prepared by the method of chemical precipitation. Typically, the diameter of particles is about 30 nm and they have relatively narrow size distribution. The gelatin with nanoparticles is a basis for making of both SHE and photopolymer with nanoparticles, but different additives are used for respective materials. We have studied the recording processes with proper detection methods which lead to the redistribution of AgBr particles within the recording layer. In the paper, we will give the main results of our findings and also some properties of the new self-developing photopolymer with nanoparticles will be presented.