Light-induced Soliton Waveguides And Optimal Phase-matching For SHG In Biaxial Crystals

In this thesis, two research subjects are involved: one is the theoretical and experimental investigation of one-dimensional PPS and their induced waveguides, and the other is the determination of the optimal phase-matching for SHG in biaxial crystals. The main work is as follows:(1) The photorefractive effect as well as the build-up mechanism of PPS is briefly introduced, and the linear electro-optic effect in two photorefractive crystals, that is, SBN and LiNbO3, is discussed. On the basis of Kukhtarev equations, the theory of one-dimensional PPS is studied in detail, and the solutions of PPS are presented in form of integrations.(2) The theory of one-dimensional PPS is solved by numerical computation, and to take it further, the dependence curves of the corresponding intensity full width at half maximum (FWHM) on the irradiance divided by dark irradiance are obtained. By employing the beam propagation method (BPM), the propagating properties of one-dimensional bright screening spatial solitons and their interactions are investigated.(3) The formation of one-dimensional dark photovoltaic spatial solitons (PVSS) is experimentally investigated in LiNbO3:Fe crystal. Planar and Y-junction soliton-induced waveguides are successfully fabricated by introducing phase perturbation and amplitude perturbation in uniform incident beams, respectively. Based on theoretical analysis and experimental investigation of the influence of the intensity gradient orientations on the formation of one-dimensional dark PVSS, a novel approach is proposed to fabricate channel waveguide in bulk crystals with one-dimensional solitons by twice exposures and experimentally demonstrated in LiNbO3.Fe crystal.(4) The phase-matching for second harmonic generation (SHG) in biaxial crystals and the corresponding effective nonlinear optic coefficients deff are discussed in detail and their accurate analytical expressions are presented. As an example, numerical treatments are performed on the phase-matching and the corresponding deff for SHG at fundamental wavelengths of 1.064μm and 0.808μm in benzophenone and accordingly, the optimal phase-matching angles are determined. Based on this, oriented growth of benzophenone for SHG is proposed, and satisfactory experimental results are achieved.