The high harmonic generation from asymmetric molecules with an $\omega +2\omega /3$ multicycle bichromatic laser pulse has been investigated. It is shown that the ionization asymmetry in consecutive half optical cycles for asymmetric molecules is further enhanced since the $2\omega /3$ control laser pulse further enhances the amplitude of the ionization peak at the center of the laser pulse. The $2\omega /3$ control laser pulse also significantly enlarges the difference of the photon energies emitted from the ejected electron in the half optical cycle at the central laser pulse and its next half optical cycle. In addition, a broadband supercontinuum is produced in the plateau of the spectrum, from which an isolated 90-as pulse can be directly obtained.

• Received 10 February 2010

DOI:https://doi.org/10.1103/PhysRevA.81.053846