Intensity Enhancement in Attosecond Pulse Generation

We present an efficient method to enhance the attosecond pulse intensity when either a model He
⁺
ion or a neutral He atom is exposed to the combination of a synthesized two-color field (800 and 1600 nm) and a high-order harmonic pulse. The results show that, by properly adding an ultrashort 13th (61.5 nm), 27th (29.6 nm), or 6th (125.2 nm), 13th (62.6 nm) harmonic pulse (corresponding to an 800 nm pulse) to the synthesized two-color field, the harmonic yields from the He
⁺
ion or the He atom are effectively enhanced by two to five or one to two orders of magnitude compared with the original two-color field case. Finally, by properly superposing the harmonic spectrum in the supercontinuum region, we can obtain an intense attosecond pulse as short as 41as (He
⁺
) and 46as (He) from our 1-D simulations.