Time-Resolved Vibrational Spectroscopy with Subpicosecond Tunable Infrared Radiation

Seeded optical parametric amplification using amplified 350 fs visible dye laser pulses has been used to generate short pulses in the mid-infrared. These infrared pulses are angle tunable from 2.5-5.5microns (with ~500 cm sup -1 bandwidth), and are used to probe a sample's transient infrared absorption following visible photoexcitation. By monitoring probe transmission through a monochromator, transform limited resolution (~15 cm sup -1) for vibrational spectroscopy can be obtained. Since the visible and infrared radiation are both derived from a single femtosecond pulse, they are synchronized. Using a variable pathlength delay, we are able to map out the evolution of the vibrational spectra of biological and organometallic species following photoexcitation.