Modulation of recording beams during grating formation

Holography has become of increasing commercial interest in recent years with significant technological developments in many areas such as data storage. Photopolymer materials such as acrylamide-based photopolymers are practical materials for the recording of holographic optical elements, as they are inexpensive and self-processing. A great deal of experimental data is available in the literature describing the diffraction efficiencies, growth curves and the angular selectivity of gratings recorded in various materials. Such testing is often carried out so as to allow a better understanding of the holographic recording processes to be developed and therefore allow material improvement. However, the majority of these discussions are based on the performance of the holographic optical element after the recording stage, once exposure is completed or using a probe beam during recording. It has been noted however, that sometimes, during recording, the recording beams are seen to vary in intensity during the fabrication of the grating. In this paper we discuss some of our recent experimental and theoretical results that attempt to explain the modulation of the transmitted exposing beams during grating formation and offer an explanation for this behaviour.