Abstract

Sum-frequency (SF) generation has developed into a convenient tool to investigate molecular layers at interfaces. One commonly associates this nonlinear optical technique with the use of tunable high-power laser sources. In the near IR such sources are easily available; consequently, in almost all studies to date the molecular system is probed through its high-frequency vibrational modes. Radiation in the mid- or far-IR is required to study the lower-frequency modes by SF spectroscopy. Powerful tunable sources in that spectral region are rare and the advances in this area result from the use of a free-electron laser.^1,2

© 1999 Optical Society of America