Study On The Photorefractive And Nonvolatile Storage Properties Of Ruthenium-ferrum Series Co-doped Lithium Niobate

The holographic volume storage is recognized as the next-generation storagetechnology due to its high storage density, fast parallel access and transfer speed.Lithium niobate （LiNbO₃, short for LN） crystal is believed to be one of the mostimportant holographic storage media because of its excellent photorefractiveproperties, such as long storage lifetime and high diffraction efficiency. However,slow response speed, weak light-induced scattering resistance and volatile duringreadout which exist in pure LiNbO₃crystal limit the practical application. Soimproving and optimizing the holographic properties of LiNbO₃crystal becomesmore and more significant in recent years. In this dissertation, a series of Ru and Fecodoped LiNbO₃crystals is grown and studied. The photorefractive kinetics formulawas proposed based on two-centered Ru and Fe codoped LiNbO₃crystal. Theinfluencing factor of photorefractive effect were studied and discussed in detail. Atlast, the nonvolatile holographic storage properties were measured by two-wavelength technology.Ru and Fe series codoped LiNbO₃crystals were grown by Czochralski method,and the crystals had no macroscopic defect and exhibited good optical homogeneity.In the process of crystal growth, optimum parameters （temperature gradient, pullingspeed and rotating speed） were selected to maintain the flat solid-liquid interface,and the nonuniform component which origined from the solute segregation wasdecreased. The defect structure and ion occupying of Ru:Fe:LiNbO₃crystals wereinvestigated by means of X-ray diffraction, OH-absorption spectra, ultravioletvisible absorption spectra. The results showed that the segregation coefficient of Zrwas close to one. The optical homogeneity of Ru:Fe:LiNbO₃and Zr:Ru:Fe:LiNbO₃crystal was measured via birefringence gradient. The results showed that Zr dpoingwould lead to the decrease of optical quality. The OH-infrared absorption spectrawere measured and fitted by means of Lorentzian function to analysis the Zr ionoccupition. The absorption edge of Zr doped Ru:Fe:LiNbO₃crystal shifted to shortwavelength compared with Ru:Fe:LiNbO₃crystal, which manifested that Zr ionswould enter the lattice by replacingNb4+Li. With the increase of Li-composition, theabsorption edge exhibited blue shift then red shift. When the doping concentrationof Zr ions exceeded its threshold Zr4+would occupy Li and Nb at the same time,Zr3+-Zr-Li Nbcomplex could form and maintained charge balance. The ions replacingmodel was proposed.The photorefractive performance of Ru-Fe series codoped LiNbO₃crystals were investigated by means of conventional two-wave coupling experiment. Thefactors which could affect the photorefractive properties of the crystals such as theincident light wavelength, Zr doping concentration, oxidation or reduction treatmentand Li/Nb ratio in the crystals were discussed. The results showed that forRu:Fe:LiNbO₃crystal, the photorefractive parameters including diffractionefficiency, response time, recording sensitivity and dynamic range at blue light（476nm） were all better than those at red light （633nm）. In addition, doping Zr ionsinto Ru:Fe:LiNbO₃crystals could dramatically enhance the blue photorefractiveproperties. When the Li/Nb ratio in Zr:Ru:Fe:LiNbO₃crystal was close tostoichiometric proportion, the response time would be further shortened. Theimprovement mentioned above was attributed to the decreasing concentration ofintrinsic defects （antisite Nb and Li vacancy）.The light-induced scattering resistance ability of Ru-Fe series codoped LiNbO₃crystals was studied by means of transmitted beam pattern distortion and light-induced scattering exposure energy flux. The influence of Zr doping, oxidation orreduction and Li/Nb ratio in the crystals on the light-induced scattering resistancewas investigated systematically. The results showed that light-induced scattering inas-grown Ru:Fe:LiNbO₃crystal was weaker than that in oxide Ru:Fe:LiNbO₃crystal.Additionally, Zr doping and increasing Li-composition could suppress the light-induced scattering in LiNbO₃crystals.The nonvolatile holographic storage of Ru:Fe:LiNbO₃crystal was measured bymeans of two-wavelength and two-color nonvolatile technology. The dominantcarries of as-grown Ru:Fe:LiNbO₃and oxide Zr:Ru:Fe:LiNbO₃crystal at476nmirradiation was holes, while the dominant carries at633nm irradiation was electrons.The nonvolatile experimental results showed that enhanced nonvolatile storageproperties were obtained in two-wavelength nonvolatile storage. This was attributedto the merits of direct writing, being in the same phase between deep trap centersand shallow trap centers as well as stronger absorption at476nm wavelength than633nm wavelength. Then the nonvolatile properties of Zr doped Ru:Fe:LiNbO₃crystals were studied via two-wavelength nonvolatile technology. Compared withthe properties of two-wavelength and two-color nonvolatile technology crystal, Zrdoping could greatly improve the nonvolatile storage properties, andZr:Ru:Fe:LiNbO₃crystal was outstanding medium for holographic storageapplication.