We show that high harmonic generation driven by an intense near-infrared
(IR) laser can be temporally controlled when an attosecond pulse train
(APT) is used to ionize the generation medium, thereby replacing tunnel
ionization as the first step in the well-known three-step model. New
harmonics are formed when the ionization occurs at a well-defined time
within the optical cycle of the IR field. The use of APT-created
electron wave packets affords new avenues for the study and application
of harmonic generation. In the present experiment, this makes it
possible to study harmonic generation at IR intensities where tunnel
ionization does not give a measurable signal.
http://iopscience.iop.org/1367-2630/13/3/033002/
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