Multiple-acceleration in “W” waveform structure for high-order harmonic improvement

Abstract

Generally, high-order harmonic generation (HHG) from atoms and molecules can be explained by the “ionization-acceleration-recombination” model and the classical results are agreement with the quantum results. In this paper, we report a multiple-acceleration process in the “[Formula: see text]” waveform structure. It is found that due to the nonzero initial velocity in the multiple-acceleration process, the emitted photon energies from the quantum results are larger than those from the classical results. Moreover, with the optimization of this “[Formula: see text]” waveform structure, much more energy can be obtained for the accelerated electron, thus leading to the improvement of the HHG. Further, with the introduction of a half-cycle pulse, the effects of the two “[Formula: see text]” structures in the “[Formula: see text]” structure on the HHG are discussed. It shows that the latter “[Formula: see text]” structure plays the more important role in HHG modulation. Finally, through the Fourier transformation of the spectral continuum, a number of sub-40 as pulses with intensity enhancements of 1 order and 2 orders of magnitudes can be obtained, respectively.