Research On Light-induced Charge Transport Process And Holographic Recording In Near-stoichiometric LiNbO₃:Fe Crystals

Because of the benefits of large storage capacity, high density, parallel transmission, highredundancy, fast addressing and so on, the optical volume holographic storage techmology show moreand more advantages in competition with other data storage technology and have a bright future,therefore it is widely concerned. The proposed of the two-color holographic storage made thenonvolatile readout come true. The main influencing factor of holographic storage is the storagematerials, so researchers focus on looking for superior storage materials. Since the photorefractivenonlinear effect of LiNbO₃crystals was found, LiNbO₃crystals have been studied widely in theapplication of holographic storage, and become one of hot research fields. Optimizing of LiNbO₃crystals becomes one of the top priorities of the research current holographic research.The doped near-stoichiometric LiNbO₃:Fe crystals are grown by TSSG method with theconcentration of Fe are0,3,5,10,25,50and100ppm in the melt. Firstly, the spectral characteristicsand Curie temperature of the crystals were measured, then the crystal composition and impuritiesoxidation/reduction status were analyzed. The characteristics of the time-evolution process andsteady-state of the ultraviolet-light-induced absorption are investigated by the pump-probe （365nmand632.8nm） method in undoped and Fe-doped near-stoichiometric LiNbO₃crystals. The relaxationtime of the light-induced absorption may be varied with different concentration of Fe in the crystals,and the relaxation processes were fitted with the different functions. The results show that the darkdecay process of light-induced absorption corresponds a stretched-exponential behavior, the variationof the decay time constant and the stretching factor following the pumping intensity were measured.According to the electronic equations, were solved numerically by forth order Runge-Kutta method tosimulate the whole process and properties of the light-induced absorption in the LiNbO₃:Fe crystals,and the results accord with the experimental data well.Next, we investigate the holographic storage properties by the two-color holographic storagemethod with the sensitizing light of365nm and the recording and reading beams of632.8nm. As theintensity of recording light stay the same, the lower the sensitizing intensity （Irec/Isenincrease） is, thelower the recording sensitivity is, however the saturated diffraction efficiency changes inversely. Thesaturated diffraction efficiency and the recording sensitivity increase with the increase of theconcentration of Fe. However, we found that when the concentration of the doped Fe is50ppm and100ppm respectively, LiNbO₃crystals have different behaviors and we made the theoretical analysisand gave a reasonable explanation. In this essay, we have performed experimental studies for the light-induced absorption andholographic storage properties of near-stoichiometric LiNbO₃:Fe. These results are of great use inunderstanding the charge transport process of light-induced absorption and physical mechanism oftwo-color holographic storage, optimizing characteristic of holographic materials, and choosingrecording scheme of holographic storage.