Oxygen dependent hologram writing and fixing in conjugated polymers storage media

Hologram writing and fixing mechanisms are examined in disordered conjugated polymer/glass composites. The conjugated polymers used were alkoxy substituted poly(phenylenevinylene) analogs and the glass matrices were zirconia-organosilica xerogels. Hologram formation mechanism is shown to be a photochromic process consisting of light induced photo-oxidation (bleaching) of the embedded conjugated polymer resulting in the formation of an absorption grating and a phase grating. IR and Raman spectroscopy show that the chemical transformations upon photo-bleaching involve chain scission and oxidation of the polymer at the vinylic position of the conjugated polymer. Oxygen removal increases hologram formation time by more than an order of magnitude and halves the total hologram efficiency. The oxygen dependence was also highly correlated with photo-bleaching of the samples and beam interaction of the writing beams. Light sensitivity was compared for several polymer/glass composites showing that the new composites and film preparation techniques are promising for blue and ultraviolet sensitive holographic materials. A hologram fixing method based on a PMMA coating, applied on the film alter hologram formation is demonstrated and shown to increase hologram erasure times by four. These important findings show that conjugated polymer/glass composites based storage media can be manufactured and fixed efficiently for a long term based on this method.