[en] We propose a scheme for achieving molecular orientation steered by the combination of a nonresonant two-color femtosecond laser pulse and a time-delayed THz laser pulse. It is shown that the molecular negative and positive orientation can be significantly enhanced by applying this scheme compared to the single femtosecond or THz laser pulse. The effects of the intensity of the two-color femtosecond laser pulse and the delay time between the femtosecond laser pulse and the THz laser pulse on molecular orientation are discussed. The molecular orientation also depends on the carrier-envelope phase of the THz laser pulse and the initial rotational temperature of the molecule. The maximal negative and positive orientation degrees calculated are ${⟨<!--\; ???\; -->\text{cos}\mathrm{\theta <!--\; ??\; -->}⟩<!--\; ???\; -->}_{\text{nmax}}=0.828$ and ${⟨<!--\; ???\; -->\text{cos}\mathrm{\theta <!--\; ??\; -->}⟩<!--\; ???\; -->}_{\text{pmax}}=0.755$, respectively. (paper)

[en] We investigated the Autler–Townes splitting in photoelectron spectra of $\text{L}{\text{i}}_2$ 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. (paper)

[en] The orientation of CO molecule controlled by two-color femtosecond laser pulse and positively chirped laser pulse is investigated theoretically. Compared with the single two-color or positively chirped laser pulse, the combination of two laser pulses with an optimized delay time can greatly improve the degrees of the positive and negative molecular orientation, respectively. The effects of intensity of two-color femtosecond laser pulse on molecular orientation are discussed, and the molecular orientation can be achieved by a calculated intensity. Additionally, the delay time between two-color femtosecond laser pulse and positively chirped laser pulse can significantly enhance the molecular orientation. Furthermore, by varying the carrier frequency and the chirp value of the positively chirped laser pulse, it is shown that the molecular orientation can be changed to some degree. The positive and negative molecular orientation can also be manipulated by adjusting the relative amplitude of the second harmonic field with respect to the fundamental. Graphical abstract: .

[en] The population transfer of a NaH molecule from the ground state $X^1{\mathrm{\Sigma <!--\; ??\; -->}}^{+}$ to the target state $A^1{\mathrm{\Sigma <!--\; ??\; -->}}^{+}$ via stimulated Raman adiabatic passage (STIRAP) is investigated. The results show that the intensity, delay time and detuning have a significant effect on population transfer. A large population transfer is observed with increased pump and Stokes intensity, especially when the pump and Stokes intensity match. Population transfer also depends on the delay time between the pump laser pulse and the Stokes laser pulse. The detuning of the two pulses influences the population transfer. Efficient population transfer can be realized under the resonant or two-photon resonant condition. (paper)

[en] Field-free orientation of OCS molecule is studied theoretically by utilizing two THz laser pulses. The effects of the center frequency of THz laser pulses and the delay time between two THz laser pulses on molecular orientation are discussed. The molecular positive and negative orientation degrees can be changed to some extent by adjusting both the carrier envelope phases of two THz laser pulses. The maximal positive and negative orientation degrees obtained are ${⟨<!--\; ???\; -->\cos <!--\; ???\; -->\mathrm{\theta <!--\; ??\; -->}⟩<!--\; ???\; -->}_{\text{pmax}}=0.951$ and ${⟨<!--\; ???\; -->\cos <!--\; ???\; -->\mathrm{\theta <!--\; ??\; -->}⟩<!--\; ???\; -->}_{\text{nmax}}=-<!--\; ???\; -->0.902$, respectively. Furthermore, the influence of the initial rotational temperature on molecular orientation is also investigated. (paper)

[en] We theoretically investigate the complete population transfer among quantum states of the ${\mathrm{N}\mathrm{a}}_2$ molecule using ultrashort pulse trains using the time-dependent wave packet method. The population accumulation of the target state can be steered by controlling the laser parameters, such as the variable pulse pairs, the different pulse widths, the time delays and the repetition period between two contiguous pulses; in particular, the pulse pairs and the pulse widths have a great effect on the population transfer. The calculations show that the ultrashort pulse train is a feasible solution, which can steer the population transfer from the initial state to the target state efficiently with lower peak intensities. (paper)