Study On Second-order Nonlinear Optical Properties Of The GeS₂-Ga₂S₃-CdS System

With the coming of information times, second-order nonlinear optical materialswill have wide applications in the fields of optical information processing, opticalsensing, and telecommunications. Among these materials, chalcogenide glasses areone of the most promising because of their low phonon energy, high refractive index,ease of fabrication and processing, and large optical second-order coefficient.In this thesis, second-harmonic generation (SHG) of GeS₂-Ga₂S₃-CdSchalcogenide glasses after electrical, electron beam poling and thermal-inducedcrystallized processes were investigated by using Maker fringe technique, togetherwith the further study on its mechanism.Maker-fringes with good symmetry have been observed within70GeS₂·15Ga₂S₃·15CdS glass after electrical poling, and the maximum values ofrelative second-harmonic (SH) intensities appear at incidence angles about+(40-50)°.The SH intensity has tight relation with poling conditions and when the electricalpoling was conducted with 5kV, 280℃and 30min, a maximum second-ordernonlinear susceptibility with 4.36pm/V is obtained. The mechanism of SHG isexplained by model of dipoles.Prominent SHG have been also observed within 90GeS₂·5Ga₂S₃·5CdS glass afterelectron beam poling. The SH intensity increases with increasing electron-beamcurrent, accelerating voltage and irradiating time. The second-order nonlinearsusceptibility is smaller than the value obtianed after electrical poling. The poledregion is located at about ten micrometers under the glass surface. The SHG stemsfrom the formation of the space-charge electrostatic field by electron beam irradiatingTransparent crystallizing glasses with CdGa₂S₄ or CdS crystals were prepared inGeS₂-Ga₂S₃-CdS glasses by thermal treatment. Their properties were characterizedby XRD, UV-Vis spectrum and SEM. The experimental and testing results show thatit is easy to control crystallization in 70GeS₂·15Ga₂S₃·15CdS glass, and the best SHGis obtained by heat treatment at 405℃for 48 hours. The SHG comes from thenonlinear optical crystals of CdGa₂S₄ or CdS. The SH intensity and pattern of Makerfringe depend on the size and distribution of microcrystal. When the size of it is lessthan 500nm and it is dense, the fine Maker fringes were observed. Inversely, theyappear weak and broad fringes patterns.Contrasting of above three methods of poling by showed that the glass with muchdefect and the relaxation of structure is fit for electrical poling; the glass in sub stableglasses region is suitable for thermal treatment.