Studies On The Optical Storage Characteristics Of Spirooxazine Doped Polymer Films

Spirooxazines (SOs) and spiropyrans (SPs) are typical organic compounds exhibitingphotochromism. Compared to SPs, SOs show better fatigue resistance and photostability andprovides a possibility of practical applications in lenses of variable optical density, displays, filtersand optical-memory devices. Photochromic feature of SOs and SPs arises from carbon-oxygen(Cspiro-O) bond cleavage of the colorless spiro form upon UV-light excitation and subsequentisomerization to colored open forms which are called photomerocyanines (PMCs). PMCs can revertto the initial spiro forms thermally or photochemically. SOs are transparent with low nonlinearoptical properties, while PMCs are blue and highly nonlinear because of their non-centre symmetryand electron conjugation. Photo-induced birefringence of spirooxazine (6'-piperidino-1,3,3-trimethylspiro[indolino-2,3'-[3H]naphtha-[2,1-b][1,4]oxazine]) (SO?p) in poly(methyl methacrylate) (PMMA)films pre-irradiated by ultraviolet light was investigated as a function of He-Ne laser (632.8nm)pumping-beam intensity. A phenomenological model, taking photo-orientation andphoto-isomerization into account, is in good agreement with the measurements. This materialexhibited a competing process between photo-orientation and photo-isomerization. Thephoto-orientation is predominant when the power density of He-Ne beam is lower; while thephoto-isomerization is dominant at relatively high power density of He-Ne beam. Photo-inducedbirefringence of spirooxazine-doped PMMA films was alternately pumped by s and p polarizedHe-Ne beams (632.8nm) of 10 mW. A dynamics of photo-induced birefringence was recorded by alinearly polarized double-frequency Nd:YAG laser (532 nm) of 0.1 mW as a probe beam. It wasfound that the transmittance signal was modulated by the polarization of the pumping beams andthe maximum of the transmittance signals in each period versus time dropped gradually to a steadyvalue. The equilibriums of photo-orientation and photo-isomerization induced by He-Ne laser werealso investigated. Real-time holographic gratings were optically recorded with a pair of interferential He-Nelaser beams (632.8 nm) in PMMA films containing SO?p pre-irradiated by ultraviolet light. Thetransformation from SO-p to photomerocyanine (PMC) was studied in detail. PMC was observed intwo forms. The holographic characteristics of the recorded gratings were dependent on thepolarization direction of the recording beams. Reversible holograms were recorded in the mediumby modulating UV light. Polarization holographic gratings were recorded in 6-cyano-1,3,3-trimethylspiro[indolino-2,3-[3H]naphtha-[2,1-b][1,4]oxazine] (SO-q) doped PMMA films. A photochemicalequilibrium was observed in holographic gratings recorded by (s,s) polarized He-Ne beams withaccompanying UV irradiation. For comparison, (s,p) polarization holographic recordings were alsoperformed. The observed maximum value of the diffraction efficiency of (s,s) gratings was higherthan that of (s,p) gratings for both SO-p and SO-q doped PMMA films. The mechanism of thephoto-dynamics of the two polarization holographic recordings for SOs was investigated in detail. Properties of lumination for spirooxazines were also studied in this paper. It was demonstratedthat the excited state of SO-p was steadier than that of SO-q in room temperature.