Chemical Applications of Lasers: Pump and Probe Studies of Femtosecond Kinetics

Pump-probe spectroscopy is a ubiquitous time-resolved optical spectroscopy that has found application to the study of all manner of ultrafast chemical processes that involve excited states. The principle of the measurement is that a "pump pulse" usually an intense, short laser pulse impulsively excites a sample, thus defining the start time for the ensuing photophysical dynamics. A probe pulse interrogates the system at later times in order to capture "snap shots" of the state of the system. Many kinds of pump-probe experiments have been devised. The present article will mainly focus on transient absorption measurements.