Optical Second Harmonic Generation for Surface Studies

The progress of surface science relies heavily on our ability to probe surfaces and interfaces. For this purpose, many techniques have been developed in the past [13.11. Recently, laser methods for material studies have advanced to a highly sophisticated level; one therefore wonders if they can also be applied to surface studies. Indeed, there have been a number of very interesting recent discoveries in this area. It is found that laser-induced fluorescence or resonant ionization can be used to probe angular, velocity, and internal energy distributions of molecules scattered or desorbed from a surface [13.21. Coherent Raman spectroscopy [13.3], laser-induced desorption [13.4], photoacoustic spectroscopy [13, 5], and photothermal deflection spectroscopy [13.6] can be used to study surface states and molecular vibrations of adsorbates. Lately, we have shown that surface second harmonic generation (SHG) is also an effective tool for surface studies [13.7]. We describe here some of our recent work on this topic.