The time-resolved visible pump/mid-IR probe setup
A Ti:-sapphire amplified laser system operating at 1 kHz (Hurricane, Spectra-Physics) in combination with a collinear optical parametric amplifier of superfluorescence (TOPAS, Light Conversion, Vilnius, Lithuania) and a home-built noncollinear OPA provide excitation pulses tunable between ~ 300 nm and 900 nm and probe pulses tunable between 3500 nm and 800 cm-1. The probe pulses, having a spectral width of ~180 cm-1, are dispersed in a spectrograph and imaged onto a 32-element array of MCT detectors. The cross correlation between pump and probe pulses is 150-180 fs, a delay line provides the opportunity to vary the delay between pump and probe to up to 6 ns. The setup is excellently suited for experiments on proteins, since a Lissajous sample scanner is available that provides a fresh sample shot for each laser shot, but returns to the same position after ~2 minutes. Typically in 1 minute of data collection the noise level in a single spectrum is 10-5 OD, implying a noise level of 30 micro-OD for a full data set in a few hours. There is also the possibility to simultaneously measure the absorption changes in the visible part of the spectrum. A more elaborate description of the capabilities of the setup can be found in (Photochem. Photobiol. Sci., 2007, 6, 501 : Femtosecond time-resolved and dispersed infrared spectroscopy on proteins). For experiments in the midIR on longer time scales a step-scan and rapid scan FTIR setup (Bruker), with a 6-ns OPO laser source, is available.
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