Field-free molecular orientation enhanced by tuning the intensity ratio of a three-color laser field

Abstract

We theoretically study the field-free molecular orientation induced by a three-color laser field. The three-color laser field with a large asymmetric degree can effectively enhance the molecular orientation. In particular, when the intensity ratio of the three-color laser field is tuned to a proper value of I 3 : I 2 : I 1 = 0.09 : 0.5 : 1, the molecular orientation can be improved by ∼ 20% compared with that of the two-color laser field at intensity ratio I 2 : I 1 = 1 : 1 for the same total laser intensity of 2×10 13 W/cm 2 . Moreover, we investigate the effect of the carrier-envelope phase (CEP) on the molecular orientation and use the asymmetric degree of the laser field to explain the result. We also show the influences of the laser intensity, rotational temperature, and pulse duration on the molecular orientation. These results are meaningful for the theoretical and experimental studies on the molecular orientation.

Field-free molecular orientation steered by combination of super-Gaussian and THz half-cycle laser pulses*

“…[7] Initially, the single intense laser field was used to realize the molecular alignment/orientation based on the anisotropic polarization and hyperpolarization interaction. [8][9][10] However, the interaction between the field and the molecular permanent dipole moment is relatively weak, which limits the improvement of orientation. To make up the deficiency of a single field, researchers designed the combination of multiple fields to enhance the molecular orientation.…”

Influence factor analysis of field-free molecular orientation

“…[18,19] Although this method can effectively improve the molecular orientation, the presence of dc field may affect the measurement of orientation. In later studies, a two-color laser field [20][21][22] and a multi-color laser field [23][24][25] have been subsequently utilized to control the field-free molecular orientation via their interaction with molecular hyperpolarizability. However, because of the weak interaction between the laser and the molecular hyperpolarizability, improving the orientation degree needs high intensity of laser pulses, which may lead to the molecular ionization and dissociation.…”