Abstract
We propose to use a low-frequency radiation in addition to the basic pump to enhance the efficiency of high-order harmonic generation following atom tunnel above-threshold ionization. This enhancement can be achieved without an increase of basic pump intensity and, consequently, without additional saturation of ionization. A static field added to the basic pump modifies photoelectron trajectories in the continuum that leads to a high-frequency extension of harmonic spectrum. This is caused by an increase in the part of recombining photoelectrons, kinetic energy of such electrons, and recombination efficiency (owing to reduced electron wave-packet spreading). An experimental realization of this effect is proposed with use of the radiation of a powerful laser and ultrashort basic pump pulses. It is shown that the maximum-generated frequency can be tripled with this technique. Also, a multiplateau structure of the high-frequency region of the harmonic spectrum has been revealed and explained.
© 2000 Optical Society of America
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