Molecular orientation in monolayers from variation of nonlinear optical generation with incident angle

Summary form only given. Second harmonic generation (SHG) has been measured in transmission from a Langmuir-Blodgett monolayer of hemicyanine as the angle of incidence of the fundamental is varied. Attempts to match the observed behvior of the SHG with predictions from the model of B. Dick et al. (Appl. Phys. B, vol. 38, pp. 107-116, 1985), which assumes that the refractive index of the monolayer is the most important parameter, were not successful. It was concluded that the refractive index of the monolayer is not the major facator in determining the form of the nonlinear signal vs incident angle. An alternative analysis where orientation of the molecular dipoles in the monolayer is the most important parameter has been used. Rotational invariance about the surface normal is assumed, and dispersion in the monolayer is ignored. With these assumptions, good agreement has been obtained between the observed and calculated dependence of the SHG on the angle of incidence when the inclination angle of the hemicyanine molecular dipoles measured from the surface normal is 40° ± 5°.