1. Ultrafast Laser and Spectroscopy Laboratory, Department of Chemical Physics, Materials Science Centre, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands, BIOSON Research Institute, Department of Biophysical Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands, and European Laboratory for Nonlinear Spectroscopy (LENS), University of Florence, Largo E. Fermi 2, 50125 Florence, Italy