Femtosecond Fluorescence Spectroscopy

In most institutions working in the field of femtosecond spectroscopy transient absorption set-ups in UV/Vis range are the “workhorses”. They feature very high time resolution and sensitivity and provide information on ground and excited states. Yet, often spectroscopic signatures overlap and discrimination between processes in ground or excited states is difficult. Here, time resolved fluorescence spectroscopy comes in handy since it exclusively reports on excited (singlet) states. We have, thus, decided to complement our spectroscopic tools with a femtosecond fluorimeter. Commonly, femtosecond fluorimeter rely on the up-conversion principle which has certain drawbacks when it comes to simultaneously acquiring complete fluorescence spectra. We have employed the Kerr effect and constructed a set-up (see Figure (a)) which is capable to record fluorescence spectra in the range of 350 to 950 nm with a time resolution of down to 70 fs. The fluorimeter has proven its capabilities in studies on a large variety of systems (see e. g. refs. [1, 2, 3]) and thereby also turned into a “workhorse”.

In Düsseldorf, we have a built a “second generation” instrument with even better characteristics. With this set up we are able to resolve even extreme fast processes like the fluorescence decay of dipicolinic acid – DPA (see Figure (b)), with a time constant of 100 fs. Due to the improvement of the optical components we can observe a spectral range down to 260 nm.