Generation of isolated sub-50-as pulses by quantum path control in the multicycle regime

We theoretically propose a method of producing single attosecond pulse by high-order harmonic generation with a two-color multicycle driver laser field. It is shown that this scheme can modulate the quantum paths by adjusting the relative phase. In the case of the short quantum path control, a broadband supercontinuum spectrum with a 93 eV spectral width can be produced which directly generates an isolated 46 as pulse without phase compensation. When the long quantum path is picked out, a harmonic continuum spectrum with a bandwidth of 101 eV appears, an intense isolated 39 as pulse with high-signal-to-noise ratio is generated successfully by superposing some properly selected harmonics, the phases of which are locked. In both cases, our simulations show that the value of the time delay between two lasers can be varied between $\ensuremath{-}0.2$ fs and 0.2 fs to keep the isolated sub-50-as pulse generation. In particular, these results are analyzed by using both classical and three-dimensional quantum-mechanical approaches.