FREE-ELECTRON LASER SPECTROSCOPY OF SURFACES AND INTERFACES

Synchrotron-radiation sources have become, since the late 1960's, one of the fundamental experimental tools for surface and interface resear ch. Only recently, however, a related type of photon sources - the fre e-electron lasers (FELs) - has begun to make important contributions t o this field. For example, FELs have been used to reach unprecedented levels of accuracy and reliability in measuring semiconductor interfac e energy barriers. We review some of the present and proposed experime nts that are made possible by the unmatched brightness and broad tunab ility of infrared FELs. Practical examples discussed in the review are supplied by our own programs at the Vanderbilt Free-Electron Laser. W e also briefly analyze the possible future development of FELs and of their applications to surface and interface research, in particular, t he possibility of x-ray FELs.