vTransient absorption is a well-known and well-established measurement technique in the femtosecond domain, and was extended into the attosecond regime using high harmonic generation in 2010. Transient absorption measures the probe pulse spectrum transmitted through the sample as a function of pump-probe delay.

vTransient absorption spectroscopy helps study the mechanistic and kinetic details of chemical processes occurring on the time scales of few picoseconds to femto-seconds. These chemical events are initiated by an ultrafast laser pulse and are further probed by a probe pulse. With the help of TA measurements, one can look into non-radiative relaxation of higher electronic states (~femtoseconds), vibrational relaxations (~picoseconds) and radiative relaxation of excited singlet state (occurs typically on nanoseconds time scale).