Photoelectron spectra for fullerenes C 60 and C 70 ionized using 800 nm laser pulses with pulse durations from 120 to 1000 fs show thermal electron kinetic energy distributions but they also exhibit angular anisotropy with respect to the laser light polarization. The effective temperature of electrons, measured along the laser polarization direction, is significantly higher than in the perpendicular direction. We explain this observation by considering that the emission of the thermal electrons is uncorrelated with the phase of the laser pulse, unlike directly ionized electrons, and, depending on the time of emission, they may experience an additional kick from the vector potential of the laser field when they are emitted from the molecule.
Bibliographical noteFunding Information:
This work has been supported by the Swedish Research council (VR), by the K. & A. Wallenberg Foundation, EaStCHEM and by a MC IEF fellowship to J.F.