Long Holographic Lifetimes in Bacteriorhodopsin Films

The D85N genetic variant of bacteriorhodopsin displays a nearly permanent lifetime of the photochromic P490 state. We present pump-probe measurements that demonstrate this behavior. However, experimental diffraction efficiency measurements made from holograms recorded in a hydrated D85N film show markedly different decay behavior, suggesting a molecular diffusion process occurring in the film. Holograms recorded with different grating frequencies display correspondingly different decay times which support this hypothesis. A thin D85N film was then fabricated which was chemically crosslinked, resulting in the elimination of diffusion of BR molecules within the polymer matrix. This film exhibits a grating lifetime on the order of weeks or more, thus allowing the long term holographic storage of information in a BR film.