Three topics will be pursued with the aid of the Presidential Young Investigator award. 1. Nonlinear optical spectroscopy will be used to investigate the properties of solid-solid interfaces. The sum-frequency signal generated by shining two beams of light onto a heterojunction (e.g., nickel silicide/silicon) is to be measured in order to probe the interfacial electronic structure. 2. A new technique in dynamical light scatteirng (diffusing wave spectroscopy) will be employed to study particle motion and the transport of light in dense colloidal suspensions. 3. Processes associated with adsorbed molecules on clean metal surfaces (e.g., cobalt and platinum), such as energy transfer, dephasing, and molecular movements, are to be investigated by ultrafast infrared spectroscopic methods.