The induced polarization enhanced birefringence in AlPS4 family: A first-principles investigation

As an important infrared nonlinear optical compound, metal-sulfur compounds have been widely used in various advanced optical systems. In this paper, the electronic structures, optical properties, and polarization under different external electronic field of AlPS4 (I222, P222,P42c) compounds have been investigated using the first-principles method. The obtained results show that all these compounds have relatively large birefringence which are 0.256, 0.096, and 0.079@1064 nm, respectively. The relatively large birefringence has relation with the induced polarization under external electronic field rather than distorted polyhedron and spontaneous dipole moment. Both AlS4 and PS4 tetragonal give main contribution to the birefringence and second harmonic gen-eration response.