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We investigated the Autler-Townes splitting in photoelectron spectra of Li 2 molecules steered by ultrashort laser pulses using the time-dependent wave-packet method. Structure of the Autler-Townes splitting was presented to analyze the information of a selective population of the dressed states. It was found that population transfer process, structure of photoelectron spectrum and pattern of Autler-Townes splitting can be controlled by adjusting the intensity, wavelength and delay time of laser pulses.

We theoretically study the field-free molecular orientation by the combination of a two-color femtosecond laser pulse and a time-delayed terahertz (THz) laser pulse, with LiH as the prototype molecule. It is shown that the molecular hyperpolarizability is a vital parameter in achieving molecular orientation according to the pre-excitation created by an intense twocolor femtosecond laser pulse. The relative amplitude of the two-color femtosecond pulse is discussed. In addition, the center frequency of the THz laser pulse is chosen on the basis of the pre-excited population distributions. The carrier-envelope phase of the THz laser pulse as well as the delay time between the femtosecond laser pulse and THz laser pulse are adjusted to achieve a high orientation degree. In addition, the effect of temperature on molecular orientation is also discussed. Finally, according to the population distributions at room temperature, the parameters of the THz laser pulse are re-optimized, and the achieved maximal orientation degree is 0.221 at 300 K.

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