Sum-frequency generation spectrometer
Sum-frequency spectroscopy is a powerful second-order non-linear optical technique with submonolayer sensitivity and high surface selectivity, that has been widely used as an in situ surface analytical method for probing buried interfaces. In a sum-frequency experiment the temporal and spatial overlap of two beams on the sample surface leads to the generation of a third light beam with frequency corresponding to the sum of the frequencies of the exciting beams. In our spectrometer one of the beams is tunable in the infrared region, and by scanning the IR frequency the vibrational spectra of interfacial molecules can be obtained. The analysis of sum-frequency spectra makes it possible to characterize the ordering, orientation and conformation of molecular species in the interfacial region, as well as the changes in these properties.