Time-resolved UV-NIR absorption spectra provide information on molecular dynamics by interrogating electronic structure following photo-initiation of some chemical process. The pump-probe technique uses a pump pulse to initiate the reaction, the dynamics of which are probed by a second time-delayed pulse. The formation and depletion of species is observed by measuring absorption changes as a function of time. Typically, a white light continuum (WLC, 350-1500 nm) is used as the probe beam.
The WLC, passes through a spectrometer before detection on either silicon (Si, UV-vis) or indium gallium arsenide (InGaAs, NIR) detector arrays. Typical sensitivity approaches ΔA 10-5 in 1 second.
The high speed (512 channel readout at up to 20 kHz) DAQs and 512 element Si and 256 element InGaAs detectors have been developed within STFC (Technology Department) and are now available commercially (Quantum Detectors).
Schematic of the Ultra transient absorption setup. The 800 nm output (red) of the titanium sapphire amplifier is used to pump the tuneable OPA for generation of the pump beam (purple) and to generate the WLC (green) using either a CaF2 or sapphire window.