Multiphoton Ionization from Multiple Orbitals of N₂ in Strong Laser Fields

We investigate multiphoton ionization (MPI) of N₂ exposed to femtosecond laser fields at 400 nm and 800 nm experimentally. Photoelectron energy spectra are measured with a high resolution photoelectron spectrometer at laser intensities up to 10¹⁴ W/cm². Prominent resonant peaks observed at 400 nm can be attributed to the resonance with molecular Rydberg states corresponding to different molecular orbitals, revealing the importance of the multiple orbitals contribution in strong field molecular dynamics.