Application of a two-color free-electron laser tocondensed-matter molecular dynamics

The possible applications of a free-electron laser (FEL), which would be modified to produce two synchronized, independently tunable picosecond pulses, are considered. At least one of the pulses would be available in thevibrational infrared region. Such an instrument would be more useful in the area of condensed-matter moleculardynamics than the conventional one-color FEL. We review briefly the dynamical processes of greatest interest incomplicated, condensed-matter molecular systems. We discuss how a one-color and a two-color FEL can be usedfor experimental measurements of these processes and the advantages that a two-color system would have overexisting technologies. We then provide a model calculation to determine the feasibility of these experimentalmeasurements. This calculation is based on the anlysis of two-color FEL's by Schwettman andSmith [J. Opt. Soc.Am. B 6, 973 (1989)]. Finally we examine the most promising applications of a two-color FEL and propose severalspecific experiments. The applications that are discussed include vibrational relaxation in molecular systems, dynamics of surfaces, photobiology and biophysics, and coherent optical measurements of intrinsically disorderedmaterials.