Asymmetric molecular harmonic assisted generation of the attosecond X-ray pulse

In this paper, we theoretically investigate the asymmetric molecular high-order harmonic emission and the attosecond X-ray pulse generation when the asymmetric molecular HeH2+ ion is exposed to an intense chirped pulse. It is found that the molecular harmonics are strongly dependent on the internuclear distance R as well as the chirp parameter, showing a smooth and intense harmonic plateau at R = 8.0 a.u. and beta = 0.4. Further, by adding a subharmonic controlling pulse with the optimised conditions, a supercontinuum with a bandwidth of 602eV can be obtained. Finally, by properly superposing the selected harmonics in the supercontinuum region, a series of isolated X-ray pulses with durations of sub-80 as are directly generated