Flow orientation and super-quadratic dependence of second harmonic intensity on the film thickness in hemicyanine Langmuir–Blodgett multilayers

Abstract Substantial in-plane optical anisotropy in Y-type Langmuir–Blodgett multilayers of a hemicyanine dye interleaved with inert material arachidic acid due to dipping-induced and “substrate”-enhanced molecular orientation was demonstrated by polarized UV-visible absorption and rotation-angle second harmonic generation techniques. We gave the first direct evidence for a super-quadratic enhancement of the second harmonic intensity with increasing film thickness due to the additional in-plane polarization.