Nonlinear Optical Studies of Molecular Adsorbates

Abstract

In recent years, the possibility of employing laser interaction with surfaces as a surface diagnostic tool has attracted a great deal of attention. Optical second harmonic generation (SHG) and sum-frequency generation (SFG) have been proven to be most effective and versatile for surface and interfacial studies.¹ By symmetry, these processes are forbidden in media with centrosymmetry, and can therefore be highly surface-specific. They have the advantages of being capable of high spatial, temporal, and spectral resolutions, suitable for in-situ, remote sensing of samples in hostile environment, and applicable to all interfaces accessible to light. Indeed, they have been applied with great success to a large variety of surface and interfacial problems¹: probing adsorption and desorption of molecules from surfaces, measuring average molecular orientation of adsorbates, monitoring surface symmetry and surface phase transitions, conducting surface microscopy and spectroscopy, and many others. Here, we shall describe a few experiments recently carried out in our laboratory using these techniques.