Photochemistry and Ultrafast Laser Spectroscopy
The UQ-PULSE laboratories were commissioned in May 2014, facilitating the study of molecular excited state dynamics on very short timescales. Our system is based on a 1 kHz 4W amplified Ti:Sapphire laser (Spectra Physics - Spitfire ACE) and Optical Parametric Amplifier (Light Conversion – Topas Prime) providing gap free sample photoexcitation from 240-2600 nm. Various detection systems are available allowing transient absorption (Ultrafast Systems – HELIOS) and time resolved fluorescence (Ultrafast Systems – HALCYONE) measurements.
The two 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.
Ultrafast spectroscopy is used to measure the kinetics for a variety of important photophysical processes in chemical and biological research, including electronic structure, photoisomerizations, energy and/or electron transfer, charge transport, optical non-linear effects, and many other processes.
Types of experiment
- Femtosecond Transient Absorption
- Sub-nanosecond Flash Photolysis
- Femtosecond Optically Gated (FOG) fluorescence
- Time Correlated Single Photon Counting (TCSPC) lifetimes
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.
Dr Evan Moore
Room 838, Chemistry Building (#68)
Phone: +61 7 336 53862
Available on application