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

We study optical second-harmonic generation by a layer of molecules ad sorbed on the hypotenuse face of a glass prism, excited from the glass side. We show that second-harmonic generation is particularly effecti ve when the angle of incidence exceeds the critical angle for total re flection. 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 ou t to be complex valued. We show that rotational intensity patterns, ob tained by plotting the second-harmonic intensity as a function of inci dent polarization angle at fixed angle of incidence, may be used to de termine 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 b y the Langmuir-Blodgett technique.