Techniques
The primary techniques available include ‘pump-probe’ Transient Absorption (TA) and Femtosecond Optically Gated (FOG) fluorescence lifetimes.
In TA spectroscopy, a tuneable ca.100 fs ‘pump’ pulse is used to initially populate higher energy excited states. A second ‘probe’ white light pulse is then used to measure the differential absorption of these species. Detection wavelengths currently available span the Visible (420-810 nm) and Near Infra-Red (850-1600 nm) regions. Using a continuum based white light source, we are able to extend the detection time window from ~200 fs (FHWM IRF) to ~1 msec.
Alternatively, fluorescent samples can be analysed using Femtosecond Optically Gated (FOG) lifetime methods. A tuneable ca. 100 fs ‘pump’ pulse is used to excite the sample, and the resulting emission is mixed with a second ‘gate’ pulse in a non-linear crystal, yielding an upconverted signal and providing the best available time resolution. Using this technique, fluorescence lifetimes with femtosecond time resolution can be obtained. Longer lived samples (> 2 ns) can be analysed using more traditional Time Correlated Single Photon Counting (TCSPC) approaches.
Sample requirements
Samples may be provided either as solutions or deposited on transparent substrate as thin films.
Fluorescent samples may also be studied in the solid state.
