Alignment control of molecules has attracted much attention for a couple of decades because it enables us to observe and manipulate molecular wave functions in a molecule-fixed frame. One of the promising applications is to make so-called molecular movies as the alignment control can initialize molecules before triggering chemical reactions. To align molecules, laser pulses are often used because of the abilities to impose controlled strong electric fields on molecules. There were, however, controversial discussions about the effective polarization conditions, right irradiation timings and so on. To answer the questions, we have applied optimal control simulation, which has been developed in our group, to best achieve the three-dimensional alignment of asymmetric-top molecules. We have found that the optimal solution is a set of mutually orthogonal, linearly polarized pulses, in which the last pulse is much more intense than the others. We also found that each pulse can be replaced by an experimentally feasible simple pulse without reducing the degrees of alignment. Thus, the present method derived by the optimal control simulation can be a powerful tool to suitably initialize molecules for many applications including molecular movies.
Locally optimized control pulses with nonlinear interactions, Y. Ohtsuki, T. Namba, J. Chem. Phys. 151, 164107 (2019).
Three-dimensional alignment of asymmetric-top molecules induced by polarization-shaped optimal laser pulses, M. Yoshida, N. Takemoto, Y. Ohtsuki, Phys. Rev. A 98, 053434 (2018);