Theoretical Study of Infrared Nonlinear Optical Crystal BaGa4Se7 Tetragonal System

Abstract

The electronic structure and optical properties of BaGa4Se7 tetragonal crystals are systematically studied by first principles of density functional theory. The band gap (2.918 eV) of the tetragonal system of BaGa4Se7 is 1.12 times that of the orthorhombic system by using the Heyd-Scuseria-Ernzerh (HSE06) method. The band structure showed that the top of the valence band was largely contributed by Ga 4s, 4p and Se 4p states, while the bottom of the conduction band was mainly comprised of Ga 4s, 4p, Se 4p, and Ba 5d states. This wide band gap effectively avoid the two-photon absorption during laser pumping and increase the laser damage threshold of the material. The orbital coupling between Ga and Se atoms determines the optical properties of BaGa4Se7 tetragonal crystals, while Ba atoms make little contribution to the optical properties. The calculation of optical properties shows that the static birefringence (0.076) of the BaGa4Se7 tetragonal crystal is 1.2 times that of the orthorhombic crystal system. It shows that the BaGa4Se7 tetragonal crystal material has excellent phase matching performance in a wide range of wavelengths. BaGa4Se7 crystal shows strong absorption and reflection characteristics in the ultraviolet region, and strong transmittance in the infrared region. Theoretical results indicate that BaGa4Se7 is a very promising nonlinear optical crystal in the infrared region.