Maximum Attainable Field-free Molecular Orientation of a Thermal Ensemble with Near Single-cycle THz Pulses

Recently single-cycle THz pulses has been demonstrated in the laboratory to successfully induce field-free orientation in gas-phase polar molecules at the room temperature. We examine for the first time the maximum attainable field-free molecular orientation with optimally shaped linearly polarized near single-cycle THz laser pulses of a thermal ensemble. Large-scale benchmark optimal control simulations are performed, including rotational energy levels with the rotational quantum numbers up to J=100 for OCS linear molecules. The simulations are made possible by an extension of the recently formulated fast search algorithm, the two-point boundary-value quantum control paradigm (TBQCP), to the mixed-states optimal control problems in the present work. It is shown that a very high degree of field-free orientation can be achieved by strong, optimally shaped near single- cycle THz pulses.\\[4pt] [1] S. Fleischer, Y. Zhou, R. W. Field, and K. A. Nelson, Rev. Lett. 107, 163603 (2011).\\[0pt] [2] T.-S. Ho and H. Rabitz, Phys. Rev. E 82, 026703 (2010)\\[0pt] [3] S.-L. Liao, T.-S. Ho, H. Rabitz, and S. -I Chu, Phys. Rev. A xx, xxxxxx (2013).(accepted)