Dark self-enhancement in dichromated poly(vinyl alcohol) gratings: a detailed study

Experimental results concerning the real-time hologram recording process in dichromated poly(vinyl alcohol) are presented. Self-enhancement, the increase in diffraction efficiency of the holographic gratings in the dark after recording, is also presented. The influence of the recording parameters (pH, exposure energy, dichromate concentration) on the self-enhancement gain is shown. Maximum gain was 6, and self-enhancement occurred during the 3 days following the exposure. The results and a model for the reduction of chromium ions corresponding to the formation of the grating are discussed.