| Field-free molecular orientation induced by a laser field has attracted extensive attention of researchers due to its widespread applications in areas such as chemical reaction dynamics, high-harmonic generation and so on. In this thesis, the time-dependent Schrodinger equation was numerically solved by using the rigid rotor approximation and the fourth-order Runge-Kutta method. We take the molecules CO as an example and investigate the orientation dynamics of diatomic molecules induced by a laser or THz field theoretically. The main works of my thesis are as follows:(1) We make comparative analysis of the orientation behaviors of the CO molecules induced by a THz pulse with different time-domain waveform with the matlab software. Taking the few-cycle THz pulse as the example, the affects to the molecular orientation of parameters such as the electric field strength, the pulse width and the temperature have been studied. In addition, we analysis the molecular orientation induced by two THz pulses, the result shows that the orientation degree can breakthrough the limit of single pulse case.(2)We also use a novel chirped THz pulse to induce the molecules and prove that the feature of increasing frequency promotes the molecular transition to higher rotational quantum states from multiple perspectives, so the higher orientation degree can be achieved. In addition, the effect of the peak field and the linear chirp rate of chirped pulses has also been discussed.(3)We propose a method by utilizing a chirped terahertz pulse in combination with a femtosecond laser pulse. The result shows that the orientation degree induced by a weak chirped THz pulse can be enhanced greatly with the pre-excitation of the laser pulse. Changing the parameters of the pulses, we have investigated the affects to the orientation degree by the field strength of the THz/laser pulse and the linear chirp rate specifically. This work provides the theoretically guidance for implementation. |
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