Transient absorption spectroscopy
using two pulses (strong pump and weak probe)
and capable of achieving a high temporal resolution. A pump
the sample and triggers the process under investigation. A second delayed pulse,
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
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 polarization
. The excitation intensity to create
the excited state
constitutes a two-field interaction and the determination of
the change in the time-dependent optical properties involves a third field monitoring
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 diffraction
pattern as a function of time.
PAC, 2007, 79, 293
(Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006))
on page 404
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook