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MO: Fachverband Molekülphysik

MO 18: Experimental Techniques

MO 18.2: Vortrag

Mittwoch, 20. März 2013, 14:15–14:30, F 102

On the Background Problem of Fluorescence Kerr Gating — •Ramona Mundt, Gerald Ryseck, and Peter Gilch — Institut für Physikalische Chemie, HHU Düsseldorf, Universitätsstr.1, 40225 Düsseldorf

Fluorescence decays in the femto- to picosecond time regime are usually traced by upconversion or optical Kerr gating [1].

Though Kerr gating commonly offers a larger spectral coverage than upconversion, it suffers from background light leaking through the gate. It consists of a pair of crossed polarisers through which a portion of fluorescence light leaks in the closed state. This becomes particularly problematic when studying long-lived fluorophores with lifetimes up to some hundred picoseconds or longer.

When employing large aperture optics to collect the fluorescence light, the leakage is predominantly due to the intrinsic depolarising properties of the optics. These properties will be presented for a gate consisting of Cassegrainian microscope objectives and wire grid polarisers [2]. Since the depolarisation is not uniform along the beam cross section, suitable apertures can reduce the background. As shown in a recent study [3] with such an aperture, measurements on long-lived fluorophores are possible. Further refinements will open the route to fluorophores with nanosecond lifetimes keeping 100 fs time resolution.

[1] G. Ryseck and P. Gilch, "Ultrafast Fluorescence Spectroscopy", Walter de Gruyter, in press [2] B. Schmidt et al., Appl. Phys. B, 2003, 76/8, 809-814 [3] T. Cordes et al., J. Photochem. Photobiol. A, 2009, 206/1, 10-17