Field-free orientation of CO molecule by combining two-color femtosecond laser pulse with time-delayed positively chirped laser pulse

The orientation of CO molecule controlled by two-color femtosecond laser pulse and positively chirped laser pulse is investigated theoretically. Compared with the single two-color or positively chirped laser pulse, the combination of two laser pulses with an optimized delay time can greatly improve the degrees of the positive and negative molecular orientation, respectively. The effects of intensity of two-color femtosecond laser pulse on molecular orientation are discussed, and the molecular orientation can be achieved by a calculated intensity. Additionally, the delay time between two-color femtosecond laser pulse and positively chirped laser pulse can significantly enhance the molecular orientation. Furthermore, by varying the carrier frequency and the chirp value of the positively chirped laser pulse, it is shown that the molecular orientation can be changed to some degree. The positive and negative molecular orientation can also be manipulated by adjusting the relative amplitude of the second harmonic field with respect to the fundamental.