<title>Real-time holographic recording in dichromated polyvinyl alcohol films: investigations on some external electron donors and effect of humidity</title>

Abstract

In this work, we present a study on the effect of four external electron donors in the formulation of dichromated polyvinyl alcohol (DC-PVA) films on the photosensitivity and real-time diffraction efficiency of volume holographic transmission gratings. The studied amines were found to have a detrimental effect on both holographic characteristics, even in small concentration. We found that higher relative humidity significantly improves the photospeed and the diffracted efficiency in DC-PVA films with and without an electron donor in almost all cases. The effect of the environmental humidity on the real-time diffraction efficiency in DC-PVA films with and without electron donors has been studied. Measurements of holographic characteristics are discussed. The photochemical recording mechanism in DC- PVA in the presence of external electron donors is briefly discussed as well. The amines may form a strong chelate ring structure with the chromium ions and, possibly, interfere with the crosslinking action of the photoreduced chromium. Crosslinking of the PVA matrix may occur either by PVA radicals or complexation of PVA with chromium. In both cases, hologram formation includes an electron transfer reaction, and the amines, good electron donors hinder the process by making chelate with the chromium.