Time-resolving molecular vibration for microanalytics: single laser beam nonlinear Raman spectroscopy in simulation and experiment.

A single-beam implementation of coherent anti-Stokes Raman scattering (CARS) allows experimentally very much simplified and flexible approaches to time-resolved vibrational spectroscopy, with the additional benefit of microscopic spatial resolution. To achieve this, a broadband femtosecond laser is combined with a pulse shaper creating tailored pulse sequences by computer control. We discuss the theoretical foundations and technical issues of the technique in detail and show the successful implementation of different schemes for truly femtosecond time-resolved vibrational spectroscopy. Hereby, we elaborate all the details of the method shown earlier in a proof-of-principle study [Von Vacano and Motzkus, Opt. Comm., 2006, 264, 488] and greatly extend it by novel approaches relying on the use of identical double pulses or additional polarization control for background-free spectroscopy with superior robustness and signal-to-noise ratio. Perspectives and applications of the presented schemes for chemical microanalysis and high-contrast chemical imaging are examined.