Tunable ultrafast infrared/visible laser to probe vibrational dynamics

A tunable, ultrafast (~100 fs-~1 ps) laser system generating mid-IR (3-10 (mu)m) and UV/visible (392-417 nm, 785-835 nm) radiation is described and its output characterized. The system is designed to explore vibrational dynamics in the condensed phase in a direct, two-pulse, time-resolved manner, using Raman spectroscopy as the probe. To produce vibrational resolution, probe pulses are spectrally narrowed by use of a long doubling crystal. Frequency-resolved optical gating is used to evaluate beam characteristics. An effective method for determining the temporal overlap of the pump and probe pulses for a one-color, 400 nm configuration is illustrated. Representative results from studies of heme and para-nitroaniline vibrational dynamics illustrate the effectiveness of the visible pump-visible probe portion of the system in illuminating fast structure and energy dynamics.