High-Intensity Harmonic Generation with Energy Tunability Produced by Robust Two-Color Linearly Polarized Laser Fields

By using the numerical solution of the time-dependent Schrodinger equation, we theoretically explored the high-order harmonic generation process under the interaction of high-intensity two-color ultrashort driving laser pulses with atoms. The symmetry of the electric field of the laser pulse will be broken. The producing electric field was controlled at the subcycle level by an IR laser and its second harmonic, which has the unique characteristic that two sequential half-cycles become distinct, rather than merely opposite in sign. Compared with the case of the atom in the fundamental laser pulse, the harmonic efficiency showed an increase of 1 similar to 2 orders of magnitude at specific harmonic order with this combined pulse action. Through the theoretical analysis with the three-step model, it was demonstrated that the enhancement of the harmonic intensity is due to the fast ionization of electrons at the ionization moment and the short time from ionization to recombination of ionized electrons. In addition, effects of the peak field amplitude ratio, the full width at half maximum, the phase delay of the two-color pulses, the laser intensity and ionization probability on the harmonic efficiency enhancement were also investigated.

Automated summary

By using numerical methods, we theoretically explored the high-order harmonic generation process when atoms interact with high-intensity two-color ultrashort laser pulses. The symmetry of the laser pulse's electric field is broken in this process. Through controlling the electric field generated by an IR laser and its second harmonic, we were able to control the produced electric field at subcycle level, which showed significant enhancement in harmonic efficiency compared to fundamental laser pulses. The enhancement is attributed to fast ionization of electrons and short ionization-recombination time.