Kerr-gated broadband femtosecond fluorescence spectroscopy is a powerful alternative to femtosecond fluoresence up-conversion. The fluorescence of the molecules in the sample solution in a 1 mm cuvette is excited by a femtosecond pump pulse and detected by a CCD detector after passing through two crossed linear polarizers and a grating spectrograph. The Kerr gate is positioned between the polarizers. Under normal conditions, the emission is nulled. However, a short near-IR gate pulse polarized at 45o with respect to the first polarizer creates an optical anisotropy in the Kerr medium, leading to a rotation of the fluorescence polarization and thereby a partial transmission through the second polarizer. The Kerr switch is open, when the gate pulse is on, and shut, when the gate pulse is off. The advantage compared the fluorescence up-conversion technique is that the entire fluorescence spectrum is detected at each pump-probe delay step. Using CCl4 as Kerr medium, we routinely reach a time resolution of ~120 fs.
- U. C. Stange, M. C. Stuhldreier, M. Malicki, C. Schüler, J. Kleber, T. Muskat, F. Temps, Manuscript in preparation.