Microscopic interactions governing phase matchability in nonlinear optical materials

Ab initio and group theoretical techniques have been used to investigate the microscopic interactions that govern phase matchability in nonlinear optical materials. Li2CdMS4 (M = Ge, Sn) diamond-like semiconductors (DLSs) have been considered as a case study for their peculiarity: despite the similar geometry and stoichiometry, the former is type I phase matchable unlike the latter. We disentangle the electronic and structural features that determine the dielectric tensor into contributions that can be singularly adjusted, in order to tune the refractive index, and thus the phase matching behavior. We suggest possible experimental routes to modulate the refractive index and hence the phase matchability in DLSs. Finally we propose a new DLS material with low phase matching threshold. Such approach can be extended to harness the optical response in other classes of nonlinear optical materials.