材料期刊网

KTiOPO4 is a positive biaxial crystal with very good nonlinear optical properties. According to the second-order nonlinear optical rule on a biaxial crystal, under the usual conditions of type II phase-matching, a slow ray (e(1)(omega)) and a fast ray (e(2)(omega)) at a fundamental frequency (the refractive index relationship is n(e1) > n(e2)) can only be transformed into a fast ray (e(2)(2 omega)) at a doubled frequency, i.e, e(1)(omega) + e(2)(omega) --> e(2)(2 omega). However, under a d.c. field applied along the c-axis of the crystal, not only is the e(2)(2 omega) ray generated, but a slow ray (e(1)(2 omega)) at the doubled frequency is also generated. The new e(1)(2 omega) ray is also linearly polarized. The 90 degrees angle between the polarization direction of the e(1)(2 omega) ray and that of the e(2)(2 omega) ray is independent of thickness in the transmission direction of the SHG element. KTiOPO4 is a typical quasi-one-dimensional ionic conductor. The phenomena investigated are caused by the quasi-one-dimensional ionic current, and can be explained using the quantum theory of photons.