An efficient field-free molecular orientation in the ground electronic state of the LiH molecule is steered by the linearly overlapping two-color laser pulses of the fundamental frequency $\omega$ and its second harmonic $2\omega$ through the quasiresonant (three-photon) hyper-Raman transitions with negligible (final) vibrational excitations, where the vibrational state $v=1$ is selected as the intermediate state. A relatively large positive detuning is needed to trigger such nearly pure rotational excitations, and the required laser intensity becomes larger with the increase of the detuning. Interestingly, it is also found that either the relative phase or the delay time between the two harmonic pulses can be used to control well the degree and direction of the field-free molecular orientation, which is closely related to the periodical variations of the resulting maximal electric fields in the positive and negative directions and indicates the dominated hyper-Raman process near the maximal laser intensity. Of course, since more vibrational excitations may occur when the delay time between the two harmonic pulses becomes larger, a considerable overlap between them is also important. Finally, the effects of the intensity and duration of the second harmonic pulse on the degree of the field-free orientation are also discussed.

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• Atomic & molecular processes in external fields
• Molecules
• Electric moment
• Polarizability
• Coherent Raman in a low pressure gas
• Coherent control
• Dipole approximation
• Molecular dynamics
• Schroedinger equation