The FCS and BIFL experiments are carried out with the confocal epi-illuminated setup depicted in Fig. 1. The fluorescent molecules under study are excited by a linearly polarized, active-mode-locked argon-ion-laser (528 nm or 496 nm, 73 MHz, 150 ps). The fluorescence is detected in a confocal microscope (objective: Olympus 60x, N.A. 1.2 immersion objective; pinhole: d = 100 µm). The collected fluorescence is divided into its parallel and perpendicular components via a polarizing beamsplitter and by dichroitic beamsplitters into wavelength ranges below (Detector 1+2) and above (Detector 3+4) 620 nm. All measurements are made on freely diffusing molecules in an open detection volume (v; = 0.5 µm, z0 = 1µm, I0 = 150 kW/cm2).