Monolayer studies by sum-frequency generation in the mid- and far-infrared using a free-electron laser

Summary form only given. Infrared-visible sum-frequency generation (SFG) has become a widely applied tool for the study of molecular monolayers. It combines the interface selectivity of a second-order nonlinear optical process with the specificity of a spectroscopic technique. A particularly attractive feature of IR-visible SFG is that by scanning the IR wavelength over the vibrational modes of the molecule one can independently probe its various subunits. We report here on monolayer IR-visible SFG in the largely unexplored spectral region beyond 6 /spl mu/m using a free electron laser.