Experimental Study of Shrinkage Dynamics of Holographic Photopolymer Materials

The dynamics of effective and physical (geometric) shrinkage of holographic photopolymer material is studied by measuring the evolution of transmission spectra of volume reflection holograms during their recording. For the first time it has been shown experimentally that physical shrinkage occurs to a significant extent at an early stage of hologram formation, when its diffraction efficiency is negligible (less than 0.05). It was established that at the end of the exposure, the effective shrinkage values for small and large grating periods differ significantly, while the physical shrinkage stays approximately the same. For the studied grating samples, estimates of the average refractive indices before and after exposure were obtained. A method and device for measuring the shrinkage dynamics of reflection photopolymer holograms have been developed, ensuring minimal errors in estimating shrinkage parameters. The research results may be useful for further studying the nature of hologram formation in photopolymer materials, as well as for practical use in the development of holographic elements and devices based on them.