Dynamics of thermal electron emission from highly excited C₆₀

Gas-phase fullerenes emit thermal electrons after femtosecond laser excitation in the wavelength range 400-800 nm. We have used angular-resolved photoelectron spectroscopy (PES) to study the influence of the laser's electric field on the dynamics of the thermally emitted electrons. The laser field introduces an asymmetry in the thermal electron distributions with respect to the laser polarization direction, which was confirmed by carrying out experiments at different wavelengths. A simple model could reproduce the trends in measured apparent temperatures in the PES. The asymmetry effect was exploited in a pump-probe experiment to estimate the time scale for thermal electron emission. It was found that, when 400 nm, 120 fs laser pulses of 2 TW cm-2 intensity are used, thermal electrons are emitted up to ca. 300 fs after the peak of the laser pulse. The pump-probe scheme should be applicable to a wider range of complex molecules and clusters showing thermal electron emission on a femtosecond time scale.