Observation of second-harmonic generation form Langmuir-Blodgett multilayers of a hemicyanine dye

Abstract Second-harmonic generation (SHG) from hemicyanine dye Langmuir-Blodgett multilayers has been investigated. Both centrosymmetric and non-centrosymmetric (alternating) structure samples were prepared and tested. Values of the second-order molecular polarizability β and its average polar angle ψ are deduced from measurements on the non-centrosymmetric films. The results are discussed with reference to the structure of the films. In particular it is noted that the unexpected observation of SHG from a nominally symmetrical bilayer must indicate a difference between the two layers.