OPTICAL 2ND-HARMONIC GENERATION FROM ADSORBATE LAYERS IN TOTAL-REFLECTION GEOMETRY

We study optical second-harmonic generation by a layer of molecules adsorbed on the hypotenuse face of a glass prism, excited from the glass side. We show that second-harmonic generation is particularly effective when the angle of incidence exceeds the critical angle for total reflection. The second-harmonic intensity is calculated as a function of angle of incidence and polarization of the fundamental wave. In total reflection the necessary linear and nonlinear Fresnel factors turn out to be complex valued. We show that rotational intensity patterns, obtained by plotting the second-harmonic intensity as a function of incident polarization angle at fixed angle of incidence, may be used to determine second-order susceptibility components of isotropic adsorbate layers. We verify the theoretical predictions for experimental samples prepared as thin organic films of highly nonlinear hemicyanine dyes by the Langmuir-Blodgett technique.