The Study On The Fabrication And Properties For β-BBO Nonlinear Optical Material

The low temperature phase of barium borate (β-BaB₂O₄, so called β-BBO) is a novel nonlinear optical (NLO) crystal, especially in ultraviolet (UV) wavelength. It has widespread application market. Recently, with the integration and miniaturization of laser techniques, in order to meet the demand of the development of femtosecond laser techniques and integration optics, to resolve the problems of group velocity mismatching, pulse spreading and so on in the β-BBO crystal which caused by the thickness, ultra-thin β-BBO crystals are needed. Since β-BBO is one of soft crystals with low mechanical strength, it is difficult to prepare micro magnitude or ultra-thin β-BBO specimen. There do exist the problems of cracking, distortion and so on in the course of grinding and polishing the sample. In order to solve these problems, preparation, properties and application of thin films of β-BBO is a subject of intense research. The aim of our current work is to search for a novel substrate and new techniques for the formation of crystalline β-BBO films. In this paper, we use Sr -doped α-BBO crystals which have been grown by Czochralski method as substrate and report the growth and the characterization of β-BBO/α-BBO composite nonlinear optical membrane material by vapor transport equilibration (VTE) techniques. β-BBO/α-BBO composite nonlinear optical membrane materials have been successfully prepared using VTE technique. This is the first attempt of fabricating β-BBO layer on Sr²⁺-doped α-BaB₂O₄ substrate by VTE. The effect of powder ratio, orientation of substrate, VTE treatment temperature and VTE treatment time in the control of orientation quality and microstructure of the films is discussed.The experimental results show that it is promising to fabricate β-BBO/α-BBO composite nonlinear optical membrane materials by optimizing the parameters of VTE techniques.