Quantum path control and isolated attosecond pulse generation in the combination of near-infrared and terahertz pulses

We present an efficient and realizable scheme for the generation of an ultrashort single attosecond (as) pulse from H atom with a 800-nm fundamental laser field combined with a terahertz (THz) field. The high-order harmonic generation (HHG) can be obtained by solving the time-dependent Schrodinger equation accurately and efficiently with time-dependent generalized pseudo-spectral (TDGPS) method. The result shows that the plateau of high-order harmonics is extended and the broadband spectra can be produced by the combined laser pulse, which can be explained by the corresponding ionization probability. The time-frequency analysis and semi-classical three-step model are also presented to further investigate this mechanism. Besides, by the superposition of the harmonics near the cutoff region, an isolated 133-as pulse can be obtained.