Resonant second harmonic generation study of Rhodamine B adsorbed onto fused silica. Models of the surface optics for calculation of the molecular orientation of adsorbate

Abstract

A resonant second harmonic generation (SHG) response of Rhodamine B dye is studied on fused silica in the geometry of total internal reflection. This response shows an extreme behaviour with surface concentration of the dye. All models of the surface optics published so far fail to explain this behaviour. The proper model must account for the Fresnel optics at the surface and absorption of the second harmonic light by the dye owing to the resonant character of SHG. The polarization dependence of the SHG signal provides a picture of the average molecular orientation of the dye molecules. Disordering in the dye layer is shown to increase with increasing distance from the surface. The spatial scale of this disordering appears to be ca. 0.6 nm.