| Nonlinear optical?NLO?materials have attracted much attention due to their unique second-order frequency doubling?SHG?characteristics.Since the 1960s,in addition to the widely used infrared nonlinear optical crystals AgGaS2,AgGaSe2 and ZnGeP2,many infrared nonlinear optical compounds have been also obtained,such as Li3VO4,Pb17O8Cl8,BaGa4X7?X=S,Se?,ATeMoO6?A=Mg,Zn and Cd?,ABX3?A=Cs,Rb;B=Ge,Cd;X=Cl,Br and I?and so on.Unlike abundant UV/DUV nonlinear optical compounds,infrared nonlinear optical compounds are still relatively rare,which prompts scientists to design and synthesis more and more infrared nonlinear optical compounds to meet demand.In this paper,the macroscopic polarization,refractive index,birefringence and second-order nonlinear optical coefficients of the non-polar optical materials ATeMoO6?A=Mg,Zn and Cd?were calculated using the First-principle based software package ABINIT and Berry-phase method.The microscopic origin of the optical response is further studied by the change of atomic charge,the effective charge of Born and the Mulliken population analysis.The results show that the stable covalent bond plays an important role in determining the refractive index and SHG response,and the anisotropic electron distribution on the covalent Te-O and Mo-O bonds plays a major role in optical anisotropic birefringence.The linear and second-order nonlinear optical properties of CsGeX3?X=Cl,Br and I?compounds were also calculated using finite field combined with density functional theory.The atomic contribution of birefringence and SHG response are analyzed using Born's effective charge,atomic charge change and SHG density method.The results obtained are in good agreement with the experimental values,and the electron density distribution nearby the fermi level is the lobe-like lone pair electrons which make the germanium-halogen polyhedron distorted.The enthalpy and halogen atoms play a major role in optical anisotropic birefringence and SHG response. |
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