STUDIES OF INTERFACIAL REGIONS BY SUM-FREQUENCY GENERATION WITH A FREE-ELECTRON LASER

The use of a Free-Electron Laser (FEL) allows the study of (non)linear optical properties of materials over unsurpassed large spectral inter vals. As an example, we report on the use of a FEL as the infrared sou rce in spectroscopic infrared-visible Sum-Frequency Generation (SFG). Employing the extremely wide tunability of the Free-Electron Laser for Infrared eXperiments (FELIX) at Rijnhuizen, we have studied the frequ ency dependence of the nonlinear susceptibility for sum-frequency gene ration in gallium phosphide between 20 and 32 mu m in great detail. We have developed a short-pulse visible laser system that is highly sync hronous with FELIX thereby creating a two-color setup that can be broa dly applied. Resonantly enhanced SFG in alpha-quartz has been used to study the relative timing stability of FELIX and the synchronized pico second-laser system.