Field-free molecular orientation by a multicolor laser field

We theoretically study the field-free molecular orientation by a multicolor laser field with a superposition of the fundamental wave and its harmonics. It is shown that the molecular orientation will be up to a maximum value pumped by the four-color laser field at the same laser intensity, and the molecular orientation direction and its degree can be controlled by varying the carrier-envelope phase of the four-color laser field. It is also indicated that the molecular orientation induced by a four-color laser field can be tremendously enhanced by applying another in-phase or out-phase four-color laser field at the beginning of the rotational wave-packet rephasing or the end of the rotational wave-packet dephasing.