, Volume 96, Issue 2-3, pp 215-231
Date: 18 Jun 2009

Sub-50 fs broadband absorption spectroscopy with tunable excitation: putting the analysis of ultrafast molecular dynamics on solid ground

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We give a full description of a state-of-the-art femtosecond transient spectrometer. The setup has been put together under full consideration of all technical and conceptual developments that became available in the last few years. Particular care was taken to avoid any unneeded components and modules.

The spectrometer is operated at 1 kHz and based on a commercial Ti:sapphire amplifier. A noncollinear parametric amplifier and frequency doubling are used to provide pump tuning from the UV to the NIR. A CaF2 based single filament white light allows for 290 to 720 nm probing. The multichannel detection is operated at the full 1 kHz rate and chopping of the pump light avoids the use of a reference channel. The resulting high detection sensitivity of better than ΔOD=10−4 allows for the simultaneous recording of the spectral features of electronic states and species with differing transition strengths.

A prism-based polychromator is employed to avoid the order sorting problem with the more than octave wide probe spectrum and to enhance the throughput. Flow cells with 200 μm windows and down to 120 μm sample thickness reduce the coherent artifact and the group velocity mismatch. This results in an overall sub-50 fs temporal resolution.