Field-free alignment dynamics of FCN molecule induced by a terahertz half-cycle pulse

The molecular alignment induced by external fields is of significance in manipulating a chemical reaction. In this paper, the field-free alignment of a FCN molecule steered by a terahertz (THz) half-cycle laser pulse (HCP) is investigated by solving the density matrix equation. It is shown that a high degree of molecular alignment can be achieved by adjusting the carrier envelope phase (CEP) of the THz HCP. The appearance of a saturation threshold for the molecular alignment by a THz HCP when the field amplitude is increased arises from the 1st-order dipole moment interaction. The effect of the central frequency on the molecular alignment, which is manipulated by a THz HCP, is discussed in detail. By changing the matching number of the THz laser pulse at different CEPS, it is found that under the same conditions, a THz HCP has a certain advantage over a few-cycle laser pulse in improving the FCN molecular alignment. Comparing with a double THz HCP, a better result of the molecular alignment can be obtained by a single THz HCP at the same rotational temperature of molecules. Copyright (C) EPLA, 2019