Quantum path control using attosecond pulse trains via UV-assisted resonance enhance ionization

We theoretically investigate the quantum path selection in an ultraviolet (UV)-assisted near-infrared field with an UV energy below the ionization threshold. By calculating the ionization probability with different assistant UV frequencies, we find that a resonance-enhanced ionization peak emerges in the region E_uvp, where E_uv is the photon energy and I_p is the ionization energy. With an attosecond pulse train (APT) centered in the resonance region, we show that the short quantum path can be well selected in the continuum case. By performing the electron trajectory analysis, we have further explained the physical mechanism of the quantum path selection. Moreover, we also demonstrate that in the resonance region, the harmonic emission from the selected paths is more efficient than that with the APT energy above the ionization threshold.