Femtosecond Photoelectron Imaging of N2 at 410 nm

Abstract

We experimentally measure the kinetic energy and angular distributions of photoelectrons of N2 as a function of 410 nm femtosecond laser intensity by using velocity map imaging technique. The strong-field multiphoton ionization of mole-cules shares many of the characteristics with those of atoms. Electron kinetic energies are nearly independent of laser intensities. The independence suggests that the electron peaks in the photoelectron spectrum actually result from a two-step process, indicative of the occurrence of real population in the intermediate states. The relative amplitudes of electron peaks indicate that in the two-step process, nonresonant population transfer dominates for low intensities, while reson-ant population transfer dominates for higher intensities