Controlling field-free molecular orientation with combined single- and dual-color laser pulses

Shian Zhang, Chenhui Lu, Tianqing Jia, Zugeng Wang, Zhenrong Sun
2011 Physical Review A. Atomic, Molecular, and Optical Physics  
We propose a scheme to achieve the field-free molecular orientation around the half rotational periods with the combination of single-and dual-color laser pulses. We show that the molecular orientation can be obtained and controlled by precisely controlling the time delay between the two laser pulses. Furthermore, we discuss the effect of the laser intensity and pulse duration of the single-color laser pulse on the molecular orientation created by the dual-color laser pulse, and show that the
more » ... and show that the molecular orientation depends on the change in the alignment degree between the odd and even rotational wave-packet contributions created by the single-color laser pulse. PACS number(s): 33.80.Wz, 33.15.Bh Molecular alignment and orientation have attracted both physicists' and chemists' interest because of their extensive applications in chemical reaction dynamics [1-3], highharmonic generation [4, 5] , surface processing [6], and attosecond science [7] . An intense linearly polarized laser field has been shown to be the most effective method to obtain the molecular alignment and orientation . For example, the molecular alignment can be realized with the single-color laser pulse [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] , and the molecular orientation can be achieved with the dual-color laser pulse [18] [19] [20] [21] , the half-cycle laser pulse [22] [23] [24] [25] , or the single-color laser pulse combined with a weak dc field [26] [27] [28] . The laser-induced molecular alignment and orientation can be obtained in both nonadiabatic and adiabatic regimes. Especially, the nonadiabatic alignment and orientation can be used to produce aligned and oriented molecules under field-free field conditions, and so are desirable for further applications in various related fields. Usually, the degrees of the molecular alignment and orientation are limited by the maximally applicable laser intensity before its intrinsic saturation and ionization. Recently, various techniques have been proposed to further enhance the molecular alignment and orientation, such as the laser-pulse trains, with the pulse separations being commensurate with the rotational period [12] [13] [14] [15] 19] , the slow turn-on and rapid turn-off laser pulse [20, 27, 28] , the shaped laser pulse [16, 17] , or the hybrid laser pulse [29] . The molecular orientation can be repeatedly obtained around the full rotational periods by applying the short two-color laser pulse [18] [19] [20] [21] . However, the odd and even wave-packet contributions around the half rotational periods cancel each other out, and so no molecular orientation for the total wave-packet contribution at these time delays is observed. In this paper, we present a scheme to obtain the molecular orientation around the half rotational periods that even exceeds that obtained around the full rotational periods. We employ two time-delayed laser pulses with the combination of the single-and dual-color laser pulses, and show that the molecular orientation around the half rotational periods can be obtained and controlled by varying the time delay between the two laser pulses. We discuss the dependence of the molecular
doi:10.1103/physreva.83.043410 fatcat:sjmotohyofh7pc7ttyq2yne4py