Formation mechanisms of multiple holographic gratings in spirooxazine-doped polymer films

Multiple holographic gratings were stored in the same location of spirooxazine doped polymer films using peristrophic multiplexing techniques. Accompanied by UV irradiation, three sets of holographic gratings with different directions were recorded and readout by the He–Ne laser (632.8 nm) and the Nd:YAG laser (532 nm), respectively. Diffraction efficiency of each grating was controlled almost uniform by adjusting recording time. It was found that the growth rate of the holographic grating recorded later was lower than that of the earlier one, resulting from the weakened anisotropic distribution and the decreased population of photomerocyanine molecules. A kinetics description of isomerization gratings, competing with orientation gratings, agrees well with experimental results. Due to the thermal stability of the isomerization grating, multiple interference fringes in the photochromic film were reserved and observed by Confocal Laser Scanning Microscope.