Hannover 2013 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 18: Experimental Techniques

MO 18.3: Vortrag

Mittwoch, 20. März 2013, 14:30–14:45, F 102

Elimination of strong two-photon-excited fluorescence using a single-beam-CARS-setup — •Alexander Wipfler, Rehbinder Jean, Buckup Tiago, and Motzkus Marcus — Physikalisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, D-69120 Heidelberg, Germany

The absence of fluorescence is often claimed to be the major advantage of Coherent Anti-Stokes Raman Scattering (CARS) experiments compared to spontaneous Raman measurements. Using ultra-short laser pulses and therefore high peak intensities may cause a strong contribution of two-photon-excited fluorescence (2PEF), which overlays the CARS signal. Especially in single-beam-CARS experiments the use of short pulses with durations in the range of 10 fs is mandatory. In our talk we will present strategies to extract the CARS contribution from measurements where strong 2PEF is present. We harness the interference of the CARS field with a local oscillator that is intrinsically generated in single-beam-CARS experiments. A double-quadrature spectral interferometry (DQSI) scheme is used to extract Raman equivalent information by subtracting CARS signals for different excitation spectra. However, the phase-shaping necessary for single-beam-CARS also affects the two-photon-absorption and therefore 2PEF is not necessarily canceled out in the DQSI scheme although it is an incoherent process. We present two phase-shaping schemes that keep the 2PEF contribution constant and allow for the complete extraction of Raman-equivalent spectra. [1] Wipfler et al. J. Raman Spec. 2012 (accepted)