Photoinduced non centrosymmetry in organic polymer material

Quasi-permanent light-induced second-order susceptibility χ⁽²⁾ in 4-diethylamino-4´ nitrostilbene (DBANS) dye embedded in a polystyrene matrix and in an industrial red plastic used for application in optics is demonstrated. The method of all optical poling consists in a seeding-type process. In a first step two beams at fundamental and second harmonic frequencies are simultaneously incident on sample. Their coherent superposition results in selective polar excitation of the molecules: orientation hole burning. The induced nonlinearity in the stilbene-dye doped polymer is attributed to the angular hole burning effect due to the weakly reversible trans-cis photoisomerization. Growth of the induced χ⁽²⁾ is monitored in real time using frequency-doubling of the fundamental beam inside the sample. Maximum efficiency is achieved within 25 minutes preparation time for the two samples. This shows that the all-optical poling technique can easily be applied to almost all dye plastic material.