Direct real-time measurement of shrinkage in photopolymer materials during recording of reflection gratings

Abstract

Photopolymer recording materials aimed at a recording of holograms, diffraction elements for manipulation of light or storing of information received great deal of attention in recent years. For their optimal application it is desirable to characterize them and to know what to expect from them. During the recording of the diffraction gratings (or elements) into this photopolymer materials (but not exclusively) there can be some volume changes of the material itself (so-called shrinkage) which consequently alter the replay performance of such gratings, for example from a perspective of a color fidelity, reconstruction conditions, or diffraction efficiency (in case of a general hologram, the deformation of a holographic image is observed). The main aim is to characterize volume changes and to minimize them with application of some precompensation method in advance and so the resulting grating will have desired properties. In this contribution, we would like to present and discuss measurement method for direct and real-time detection of such volume changes for reflection gratings in low shrinkable photopolymer materials. This measurement method is based on a reconstruction of the grating with low intensity white light under slightly different angle than the angle of the recording is and the analysis on the idea of fringe plane rotation model. For a theoretical background the Kogelnik’s Coupled Wave theory and Rigorous Coupled Wave Analysis are used. The recording of the diffraction gratings and measurement of their volume changes is experimentally done for a photopolymer material Bayfol HX101.