TRANSIENT PHASE-CONJUGATION IN DYE-DOPED POLYMER SATURABLE ABSORBERS

Dye-doped polymer saturable absorbers are an important class of nonlin ear optical materials when nonlinear interactions like four-wave mixin g and two-wave mixing can be observed even at low laser intensities. T he modulation of the nonlinear absorption coefficient of the dye mediu m by an appropriate interaction of laser radiation can be utilized to generate a large phase conjugate (PC) signal in degenerate four-wave m ixing geometries. By probing this population grating at time scales le ss than the dye relaxation times very high transient PC signals can be observed. Here we report on the generation of transient PC signals us ing azo dye-doped polymer films, by delaying the arrival time of the b ackward propagating pump beam with respect to the grating writing beam s. A theoretical analysis of this delayed four-wave interaction is giv en to explain the large transient gain in the phase conjugate intensit y. Experimental observations on the magnitude of the transient gain al ong with its dependence on various parameters like the intensity of th e interacting beams, the number density of the saturable absorbers, th e read beam time delay, etc. are also presented. (C) 1997 Elsevier Sci ence B.V.