Controlling Orientation Of The OCS Molecule Using THz Laser Pulses

Molecular orientation,which is widely used in the fields of ionization dissociation,ultrafast molecular imaging and generation of higher harmonics,has been an important research topic in the field of ultrafast optics.In this paper,OCS molecules are used as models to control the molecular orientation by the combination of two terahertz laser pulses.When the laser pulse is over,the degree of molecular orientation is periodically changed and the period is equal to the rotation period of the molecule.Compared with one bunch of terahertz laser pulses,the combination of two terahertz laser pulses can effectively improve the orientation of the molecule.We have studied the effect of the center frequency of the laser pulse on the molecular orientation.When the center frequency of the first pulse is changed from 0.05 THz to 1 THz,both of the molecular orientations increases first and then decreases.When the center frequency is 0.1 THz,the negative orientation of the molecule is the largest.When the center frequency is 0.2 THz,the positive orientation of the molecule is the largest.The positive and negative orientations of the molecule present a periodic change with the delay time between the two terahertz laser pulses.The second terahertz laser pulse frequency also affects the molecular orientation degree.The THz laser pulses used in the calculation have few cycles,so changing the carrier envelope phase will affect the positive and negative asymmetry of the pulse electric field and will further affect the molecular orientation.In this paper,by adjusting the carrier envelope phase of two terahertz laser pulses,we get the maximum positive and negative degree of orientation were cos?_pmax=0.951 and cos?_nmax=-0.902.As the initial rotational temperature continues to increase,the molecular orientation will be reduced.However,the molecular orientation still has a large duration when T = 5 K.The combination of two terahertz laser pulses can obtain high orientation degree of the molecule.We can improve the positive and negative orientation of the molecule by changing the center frequency of the pulse,the delay time and the carrier envelope phase.