High-order harmonic generation and attosecond extreme-ultraviolet source generation have been theoretically investigated by controlling the two-color polarized gating field combined with the unipolar pulse. The results show that by properly optimizing the polarized two-color field as well as the unipolar pulse, not only is the harmonic cutoff remarkably extended, but the single short quantum path has also been selected to contribute to the harmonic spectrum, resulting in a 313 eV less modulated supercontinuum. Classical and quantum analyses are shown to explain the harmonic emission process. Finally, the proper superposition of harmonics, a series of isolated sub-50 as pulses, can be obtained.
High-order nonlinear dipole response characterized by extreme ultraviolet ellipsometry
