Field-free one-dimensional alignment of ethylene molecule

We report an experimental study of nonadiabatic laser-induced molecular alignment of ethylene (C₂H₄) using a linearly polarized short laser pulse of moderate intensity. The information about the confinement of the CC bond axis along the direction of the applied electric field is obtained by measuring the depolarization of a second short pulse of weak intensity interacting with the molecules after they have been exposed to the first pulse. The experimental data are compared with the numerical simulation of the Schr\"odinger equation written for the nonresonant interaction of an asymmetric top rigid rotor with a linearly polarized electric field. The field-free alignment is described by analyzing the time evolution of the angular distribution of the molecular axes together with the expectation value of the relevant squared direction cosine matrix elements.