SINGLE-VALUED DETERMINATION OF 2ND-ORDER NONLINEAR SUSCEPTIBILITIES BY QUARTER-WAVE-PLATE ROTATION

We present a new technique to determine the complex-valued tensor comp onents of the nonlinear surface susceptibility chi(S)((2)) of isotropi c adsorbate layers. It is based on a change of the state of the fundam ental polarization by rotation of a quarter-wave plate. We verify the theoretical predictions by measurements on a Langmuir-Blodgett film of a highly nonlinear hemicyanine dye in total reflection geometry. The obtained second-harmonic rotation pattern is analyzed in Fourier compo nents, which are related to the absolute value and relative phase of t he tensor components of the surface susceptibility. We compare the obt ained results with separate measurements in which a half-wave plate is used to rotate the fundamental polarization. Our results are confirme d by an additional interference experiment. The method presented here allows the single-valued determination of chi(S)((2)) with measurement s at only one angle of incidence, in contrast to the half-wave-plate t echnique.