Enhanced high-order harmonics and an isolated short attosecond pulse generated by using a two-color laser and an extreme-ultraviolet attosecond pulse

An efficient method to generate an isolated short attosecond pulse is presented theoretically. We show that, by adding a 0.5 fs, 62.3 nm extreme ultraviolet (xuv) attosecond pulse to a synthesized two-color field at a proper time, the harmonic intensity is effectively enhanced by 1-3 orders of magnitude compared with the two-color case and the harmonic spectrum higher than 260th order reveals an ultrabroad xuv supercontinuum. In addition, the short quantum path is selected to effectively contribute to the high order harmonics, and an isolated 40 as pulse is obtained. Our calculated results also show that, by adding a 0.5 fs, 29.6 nm xuv attosecond pulse to the synthesized two-color field at a proper time, the enhancement of the high-order harmonics and an ultrabroad xuv supercontinuum is observed, and the selection of the long quantum path can be achieved, then an isolated attosecond pulse as short as 39 as is generated.