Strongly driven rotor: angular focusing, squeezing and rainbow formation

Summary form only given. A strong enough laser field can create the so called pendular molecular states that are hybrids of field-free rotor eigenstates. By adiabatically turning on the laser field, one may trap a molecule in the ground pendular state, thus leading to a certain molecular alignment. The only way to achieve a considerable angular squeezing in this approach is by increasing the intensity of the orienting field. Behavior of molecules in general strong time-varying fields is a much less studied problem. Here we found some generic features in the evolution of a strongly driven quantum rotor. We show that for strong enough fields a sharp peak in the rotor angular distribution can be achieved via time-domain focusing phenomenon. In the post-focusing regime, spectacular rainbow-like structures appear in the rotor angular distribution. Generation of multiple foci and angular rainbows due to quantum revival phenomenon is also found. The predicted coherent effects have much in common with the caustics formation in wave optics, and rainbow-type scattering in optics and quantum mechanics.