Study of few-optical-cycles generation of high-order harmonics

The high-order harmonic generation process was studied using laser pump pul ses of different duration, down to 7 fs. The time profile of this kind of p ulse corresponds to a few optical cycles at the fundamental frequency, and therefore a cycle-to-cycle variation of the maximum amplitude occurs. These facts violate the adiabatic approximation of the generation process, givin g rise to new aspects of the physical process. The comparison of results wi th pulses in the two regimes are reported and discussed. The modeling of th e complete generation and propagation process in three dimensions is also p resented.