4 research outputs found
High-order harmonic generation with a strong laser field and an attosecond-pulse train: the Dirac Delta comb and monochromatic limits
In recent publications, it has been shown that high-order harmonic generation
can be manipulated by employing a time-delayed attosecond pulse train
superposed to a strong, near-infrared laser field. It is an open question,
however, which is the most adequate way to approximate the attosecond pulse
train in a semi-analytic framework. Employing the Strong-Field Approximation
and saddle-point methods, we make a detailed assessment of the spectra obtained
by modeling the attosecond pulse train by either a monochromatic wave or a
Dirac-Delta comb. These are the two extreme limits of a real train, which is
composed by a finite set of harmonics. Specifically, in the monochromatic
limit, we find the downhill and uphill sets of orbits reported in the
literature, and analyze their influence on the high-harmonic spectra. We show
that, in principle, the downhill trajectories lead to stronger harmonics, and
pronounced enhancements in the low-plateau region. These features are analyzed
in terms of quantum interference effects between pairs of quantum orbits, and
compared to those obtained in the Dirac-Delta limit.Comment: 10 pages, 7 figures (eps files). To appear in Laser Physic