Molecular orbital tomography from multi-channel harmonic emission in N ₂

High-order harmonic generation in aligned molecules can be used as an ultrafast probe of molecular structure and dynamics. By characterizing the emitted signal, one can retrieve information about electronic and nuclear dynamics at the attosecond timescale. In this paper, we discuss the theoretical and experimental aspects of molecular orbital tomography in ^N2 and investigate the influence of multi-channel ionization on the orbital imaging. By analyzing the harmonics' spectral phase as a function of the driving laser intensity, we address two distinct cases, which in principle allow the orbital reconstruction. First, the contributions from two molecular orbitals could be disentangled in the real and imaginary parts of the measured dipole, allowing to reconstruct both orbitals. Second, by decreasing the driving laser intensity, the transition from a multi-channel to a single-channel ionization regime is shown. The latter approach paves the way towards the generalization of tomography to more complex systems.