Study On The Nonlinear Optical Properties Of A Few Metal Oxides

Metal oxide materials have received a lot of attention because of their uniqueoptical, electric, and magnetic properties. It is very promsing for using oxidematerials in device applications in the future. But oxides often have complex crystalstructures, they are more difficult to fabricate than metals and semiconductors. Theimpurities and defects inside the materials obstruct wide-spread applications of metaloxide. In this thesis we optimized the growth conditions and defects of several metaloxides, improved the material quality and modified the physical properties.In Chapter1, we briefly introduced several metal oxides and the growthprocesses adopted in this thesis.In Chapter2, LiNbO₃:Zr crystals were grown and investigated. LiNbO₃:Zr wasknown to be one of the best photo damage resistant crystals in the visible region. Bystudying the ultraviolet （UV） photorefractive properties, we found that the ultravioletphotorefraction was restricted effectively. The diffraction efficiency of2mol%Zrdoped lithium niobate was only0.1%. The corresponding refractive index changewas one order of magnetitude smaller that that of normally pure lithium niobate, theintensity threshold of resistance to UV optical damage was10⁵W/cm². Zr dopedcrystals was the first reported UV photo damage resistant crystal. Through analyzingthe erasing curve, we found that there were two kinds of UV photorefractive centers,one model of light induced charge transport was proposed under ultraviolet lightillumination.In Chapter3, we designed and grew triply doped LiNbO₃:Zr,Fe,Mn andLiNbO₃:Zr,Cu,Ce crystals, and investigated the nonvolatile holographic storageproperties. By doping Zr elements into doubly doped lithium niobate crystals, theresponse time of LiNbO₃:Zr,Fe,Mn was shortened very much, being less than onesecond; The sensitivity was1.31cm/J，which was tens of times larger than that ofLiNbO₃:Fe,Mn. The sensitivity of LiNbO₃:Zr,Cu,Ce crystal was also improved toabout0.099cm/J, equivalent to that of near stiochrometric LiNbO₃:Cu,Ce crystal.The ligh induced scattering were also studied for these two kinds of triply doped crystals, our experimental results indicated that triply doped lithium niobate crystalswere the promising candidate for nonvolatile holographic data storage.In Chapter4, we grew CuScO₂thin films using plused laser deposition （PLD）method. CuScO₂is an excellent wide band gap semiconductor, the band gap ofwhich is4.35eV，the binding energy of exciton is about0.4eV. The transmissionchange was investigated under exciaton of4.6eV photons, the time race included adelayed raise-up and exponential decay component, the thermalization andrecombination time were10ps and0.75ns, respectively. These features could bedescribed within the framework of generalized many-body Elliott model.In chapter5, The EuO thin films were grown on YAlO₃substrate by PLDmethod. The optical and magnetic properties were investigated. We found that afterfemtosecond laser pulse exciation, the magnetization was first enhanced and thenbecame demagnetized. Throug studying the magnetization dyanmcis under differenttemperatures, we thought that the magnetization enhancement was due to f-dexchange interaction via free electrons generated by optical pulses, thedemagnetization was related to the thermal effect of laser exciation, these two effectswere competing with each other. We also found precession dynamics and inverseFaraday effect in EuO, achieving non-thermal control of magnetization.In Chapter6, we summarized the work of this thesis, and prospected the futurefor the research and device applicaton of metal oxide.