  We theoretically demonstrate a scheme for tomographic reconstruction of
asymmetric molecular orbitals based on high-order harmonic generation with a
two-color multicycle laser field. It is shown that by adjusting the relative
phase of the two fields, the returning electrons can be forced to recollide
from one direction for all the orientations of molecules. Thus the
reconstruction of the asymmetric orbitals can be carried out with multicycle
laser field. This releases the stringent requirement of a single-cycle pulse
with a stabilized and controllable carrier-envelop phase for the tomographic
imaging of asymmetric molecular orbitals.
