Postpulse alignment of molecules robust to thermal averaging

Alignment of molecules under field free conditions with negligible vibrational or electronic excitation is created by a short off-resonant low frequency laser pulse. Typically the global maximum in postpulse alignment occurs at a rotational wave packet revival close to half a rotational period after the short pulse. The alignment effect is robust to thermal averaging at the revivals, but averaging cancels the alignment in between. The permanent dipole-field interaction can be efficient for alignment with off-resonant frequencies between the rotational and the vibrational frequencies of the molecule. (C) 2001 American Institute of Physics.