Co-located permanent photochromic and erasable photorefractive holographic images

The dual nature of Lemke-e allow us to write both permanent and erasable holographic gratings in the same storage volume. In the presence of a triplet excited sensitizer, Lemke-e undergoes a photochemical reaction allowing the storage of permanent photochromic holographic gratings. At wavelengths longer than the triplet state of the sensitizer, the composite behaves photorefractively, allowing the storage of erasable holograms in the same location as previously stored permanent photochromic holograms. Photochromic gratings can be written in less than one minute while photorefractive gratings can be written in less than one second. The photochromic gratings have a dark lifetime of several days. Storage times, write times, read cycles and multiplexing results are also presented.