Control of Quantum Rotation and Molecular Alignment by Laser Pulses Driven rotor is a standard textbook model in the nonlinear dynamics research. Together with the harmonic oscillator, it is one of the most studied physical systems. Recently, we revisited the problem of a kicked rotor in order to find new mechanisms for laser control of molecular rotational states, and especially for the process of molecular alignment (orientation) by laser fields. Short and strong laser pulses (several hundred femtoseconds for typical diatomics) create molecular rotational wave packets that acquire aligned shape after the end of the pulse, i.e. at field-free conditions. Such a transient molecular alignment may find numerous applications in the problems of chemical reaction dynamics, surface processing and ultra-fast optics. We found that free evolution of any strongly kicked quantum rotor is subject to several semi-classical catastrophes manifested in the angular distribution singularities. The time-dependent wave function demonstrates spectacular phenomena that have analogs in atmospheric optics: focusing, rainbow and glory. How to choose excitation parameters? As a result of the new understanding of the kicked rotor dynamics, we solved the problem of dynamical alignment (orientation) by time-dependent fields, and suggested a strategy of "accumulative angular squeezing." In this scheme, a specially tailored aperiodic train of short kicking pulses gradually reduces the angular width of a rotational wave packet, and leads to an unlimited angular localization of a rigid rotor (even at finite temperature). Currently, we are applying the optimal control theory to designing laser pulses for efficient control of the molecular rotation. This research have already provided the guidelines and defined conditions for experiments on enhanced molecular alignment, which were performed by several experimental groups in 2003. Our method suggests a regular way for generating macroscopic samples of highly aligned (and, at certain conditions, oriented) molecules. Generation of ultra-short laser pulses, control of high harmonic generation and molecular lithography are only a few examples of applications that need such states.

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• I. Sh. Averbukh, R. Arvieu, and M. Leibscher, "Controlling quantum rotation with light", in “Coherent and Quantum Optics VIII” (Plenum, 2002); quant-ph/0201051.
• M. Leibscher, I.Sh. Averbukh and H. Rabitz, "Molecular alignment by trains of short laser pulses", Phys. Rev. Lett. 90, 213001-1 – 213001-4 (2003).
• M. Leibscher, I.Sh. Averbukh and H. Rabitz, "Optimal molecular alignment by laser pulses", Phys. Rev. A (in press) (2004).
• M. Leibscher, I.Sh. Averbukh, P. Rozmej, and R. Arvieu "Semiclassical catastrophes and accumulative angular squeezing of a kicked quantum rotor", Phys. Rev. A (in press) (2004), quant-ph/0306146.