In transient absorption spectroscopy, a sample is first excited with a laser pulse (pump), promoting molecules to higher energy states. A second, time-delayed light pulse (probe) then measures the absorbance changes as the molecules return to their ground state or transition to other excited states. By varying the delay time between the pump and probe pulses, the time evolution of transient species can be monitored. The technique is essential for studying non-emissive states and photochemical reaction intermediates. It is extensively used to study new solar energy harvesting systems and photocatalysts.
Transient absorption spectrometers can be split into two types; ultrafast and nanosecond. Ultrafast transient absorption spectrometers use a femtosecond laser as the pump and the probe and study dynamics on the femtosecond to short nanosecond timescales. Nanosecond transient absorption spectrometers use a nanosecond laser as the pump and a flashlamp as the probe and study longer timescale dynamics.
