Importance of quantum orbits in continuum-continuum harmonic generation

The ab initio trajectory analysis in the few cycle laser pulse presents a clear contribution of all quantum orbits in the continuum-continuum harmonic generation via interference of associated wave-packets. Based on the empirical formulas, the relative intensities of these harmonics are estimated which are in good agreement with the results of simulation. Using time-frequency analysis and by means of the classical model, the role of higher-order return trajectories in an intense infrared laser can clearly be seen in the barrier-suppression ionization regime.