Spatial distribution and quantum trajectory control of the molecular harmonic spectra from H[Formula: see text] are theoretically investigated through the combination of a few-cycle 800[Formula: see text]nm pulse and a half-cycle pulse. Results show that by properly adding the half-cycle pulse, the harmonic cutoffs from the recombination process are extended, and the harmonic intensities from the positive-[Formula: see text] direction are suppressed. Moreover, as the internuclear distance increased, the modulations on the harmonic spectra are reduced. The time-dependent wave function and the time-frequency analyses of the harmonic spectra are shown to explain the above physical mechanism. Further, by adding the laser pulse to the bowtie-shaped gold nanostructure separated by an air gap [Formula: see text][Formula: see text]nm, much higher harmonic cutoff order can be obtained in the positive-[Formula: see text] region. Finally, two isolated attosecond pulses with the full width at half maximum of 34as and 31as are obtained.
Half-cycle pulse acting on a one-dimensional Rydberg atom: Semiclassical transition amplitudes in action and angle variables
