Research On Photochromic Effect And Holographic Recording In Doubly-doped LiNbO₃ :Fe:Mn Crystals

Holographic data storage using photorefractive effect has been extensively investigated since it was proposed by Chen, et al., in 1968. The researches focus on storage materials, recording methods, light sources and fixing hologram. Two-color holographic storage realized the all-optical nonvolatile readout, which offers the probabilities of the application of holographic storage. Recently, with the development of crystal growth method, researchers pay more attention to near-stoichiometric LiNbO₃ with good optical properties. In this thesis, we systemically investigate the photochromic effect and holographic storage properties of the doubly-doped near-stoichiometric LiNbO₃, and explain the results in principle.The doubly-doped near-stoichiometric LiNbO₃:Fe:Mn crystals are grown by TSSG method with the ratios of Mn:Fe=50ppm:100ppm, 50ppm:250ppm, 50ppm:500ppm, respectively. The crystals are annealled in the oxygen atmosphere for 6hrs, 10hrs, and 18hrs, respectively. The photochromic effect of the samples is studied by comparing the transmission spectra before and after the illumination of the light of 405 nm, and the dynamic processes of the photochromic effect are investigated by using the pump （405nm）-probe （633nm） method. The higer the pump intensty is, the faster the absorption change is, and the more the absorption coefficient changes. Both the absorption change speed and the saturated absorption change increase with the increase of the Fe concentration. In our experiments, the oxidizing time seems no obvious effect on the photochromic effect, because after 6hrs oxidization, the oxidization states of the crystals have been saturated. The experimental results are reasonably explained by electron transport equations with two-center model.Next, we investigate the holographic storage properties by the two-color holographic storage method with the sensitizing light of 405nm and the recording light of 633nm. As the recording light fixed, the lower the sesitizing intensity （Irec/Isen decreases） is, the lower the recording sensitivity is, however the saturated diffraction efficiency changes inversely. The saturated diffraction efficiency and the recording sensitivity increase with the increase of Fe concentration. The annealling time in oxygen atmosphere still has no effect on the holographic storage properties, such as happenned in the photochromic effect. The results are qualitatively explained with photochromic effect.The above results of photochromic effect and two-color holographic recording of SLN:Fe:Mn crystals are very useful for understanding physical mechanism of two-color holographic storage, optimizing characteristic of holographic materials, and choosing storage method.