Biphotonic holographic grating recordings for different polarization configurations in spirooxazine-doped polymers

Spirooxazine-doped polymers exhibit a fast photochromism response and high polarization sensitivity after irradiation in the short-wavelength range. Based on such properties, holographic grating recordings accompanying a linearly polarized blue-violet beam (405 nm) in a photochromic film were performed by two coherent green beams (532 nm) for s-s, p-p, s-p left-to-right circular polarization and right-to-right circular polarization. Under the biphotonic action of 405 and 532 nm, the temporal evolution of the diffraction efficiency was strongly dependent on the polarization configuration of the recording beams. It was found that the blue-violet irradiation plays a dual role in holographic recordings: generation of merocyanine aggregation and induction of anisotropy. The experimental results were precisely fitted with a phenomenological model, assuming the simultaneous formation of one absorption grating induced by the 532 nm light and two coupling phase gratings generated from the refractive index changes by recording and auxiliary beams. The existence of absorption and phase gratings was proved by observing the florescence emission of holographic gratings and testing the dependence of the diffraction efficiency on the reading beam polarization state, respectively. The results provided a good deal of insight into the photochromic behavior of spirooxazine in polymers and created a new range of applications in the field of high-density optical storage.