< 200 fs Transient Absorption (350 - 1600 nm) Spectroscopy

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.

To remove shot to shot laser instability the probe intensity is monitored with and without sample simultaneously by splitting the probe beam and passing it through two identical spectrometers onto two identical silicon (Si, UV - vis) or indium gallium arsenide (InGaAs, NIR) detector arrays. Real time processing of the spectra and data processing algorithms are used to maximise signal to noise further. Typical sensitivity approaches ΔA 10-5 in 1 second.

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).

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