Transient absorption spectroscopy using two pulses (strong pump and weak probe) and capable of achieving a high temporal resolution. A pump
pulse excites the sample and triggers the process under investigation. A second delayed pulse, the probe,
monitors an optical property. By varying the time delay between the pump and probe pulses, it is possible to assemble measurements as a function of time. The probe pulse is typically a UV, visible or infrared pulse in which case a snap-shot spectrum is taken as a function of the delay time. Often the probe pulse is generated from a portion of the excitation beam, but it can also be an independently generated electromagnetic pulse.
In the case of an optical probe, this interaction is formally a non-linear optical process that is third-order in @P04712@. The excitation intensity to create the @E02257@ constitutes a two-field interaction and the determination of the change in the time-dependent optical properties involves a third field @MT06831@ the induced time-dependent changes in the 'linear susceptibility'. Diffractive probes (e.g., electrons and X-rays) can also be used, in which case one measures a @D01711@ pattern as a function of time.
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 404 (https://doi.org/10.1351/pac200779030293)