Classical effect for enhanced high harmonic yield in ultrashort laser pulses with a moderate laser intensity

摘要

We study the influence of the pulse duration on high harmonic generation(HHG) with exploring a wide laser-parameter region theoretically. Previousstudies have showed that for high laser intensities near to the saturationionization intensity, the HHG inversion efficiency is higher for shorter pulsessince the ground-state depletion is weaker in the latter. Surprisingly, oursimulations show this high efficiency also appears even for a moderate laserintensity at which the ionization is not strong. A classical effect relating toshorter travel distances of the rescattering electron in shorter pulses, isfound to contribute importantly to this high efficiency. The effect can beamplified significantly as a two-color laser field is used, suggesting aneffective approach for increasing the HHG yield.