Abstract

We report on an investigation of widely tunable frequency-response conversion of signals and images based on the three-photon noil-resonant processes of sum- and difference- frequency generation (SFG, DFG) under conditions of noncritical phase-matchings (PM) in a series of uniaxial crystals (e.g., LiIO₃, AgGaS₂, HgGa₂S₄, CdSe) aud biaxial ones (e g., KTP, LBO and others). Peculiarities of the conversion process have been analysed in the vicinity of the singular points on the PM surface where double noncriticality of nonlinear processes both in frequency and in the angular divergence of the signal (ω_s) radiation (the “group center (GC))^1,2 or in the angular divergence of the interacting waves (the “tangeutial center” (TC)) are realized.

© 1996 IEEE