Nonadiabatic quantum path analysis of the high-order harmonic generation in a highly ionized medium

The nonadiabatic saddle-point method is used to investigate the process of high-order harmonic generation in a gas, driven by few-optical-cycle pulses with above-saturation intensity and controlled electric field. The peculiar effects produced on the generation process by temporal reshaping of the driving field, induced by propagation in a highly ionized gas cell, can be used to control the electron quantum paths, which contribute to the harmonic generation process. It is shown that complete spectral tunability of the harmonic peak position over the entire extreme-ultraviolet spectrum, obtained by changing the carrierenvelope phase of the driving pulses, can be understood by considering the effects of driving pulse distortions on the phase of the relevant electron quantum paths. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.