Picosecond diode lasers can be used for two-photon excitation of typical fluorophores used in biomedical spectroscopy. A 10 mW, 785 nm, 300 ps pulse width, 50 MHz repetition rate ps diode laser was focused into a dye cell by an NA = 0.4 microscope lens. The fluorescence was detected by a cooled GaAs-cathode PMT and recorded by time-correlated single photon counting (TCSPC). A count rate of 4500 photons per second was obtained from a 10-3 mol/l Rhodamine 6G solution.
