Isolated short attosecond pulse generated using a two-color laser and a high-order pulse

An efficient method to generate an isolated short attosecond pulse is investigated theoretically. A broadband extreme ultraviolet supercontinuum harmonics can be generated when a model He+ ion is exposed to the combination of an intense few-cycle laser pulse and a low-frequency field. By properly adding a 27th harmonics pulse to resonantly excite the He+ ion, the intensity of the high-order harmonic generation (HHG) plateau is enhanced by 3-4 orders of magnitude. As a result, an isolated 24-as pulse with a bandwidth of 138 eV can be obtained directly from the supercontinuum around the cutoff of HHG.