Effect of a depth attenuated refractive index profile in the angular responses of the efficiency of higher orders in volume gratings recorded in a PVA/acrylamide photopolymer

A great deal of research has been carried out recently in the field of volume gratings recorded in photopolymer material. The existence of different models that predict the mechanism of hologram formation inside photopolymers, has increased the possibilities of an accurate understanding of the processes involved inside photopolymers during the exposure process. A great deal of experimental research has been done, in order to test the theoretical assumptions. Nonetheless, there is little quantitative data available about higher harmonics components of the refractive index. This is due to the fact that, apart from a few works, Kogelnik's coupled wave theory has been used to fit the temporal evolution of the diffraction efficiency of the first order. The use of this theory does not allow us to obtain information about higher orders and consequently about the higher harmonics in the refractive index. In this paper we apply an algorithm based in the rigorous coupled wave theory to reproduce the angular response curves of the different orders that propagate inside the hologram. This study will be done for attenuated in depth grating profiles. Experimental data for the angular responses of the first and second orders, centered at first and second on Bragg angular replay conditions, will be examined. The experimental data provided will demonstrate that attenuation occurs inside the hologram during the recording step, most probably because of Beer's Law. The information provided in this work is significant, since future theoretical models of grating formation in photopolymers should explain this behaviour. (C) 2004 Elsevier B.V. All rights reserved.