Measurement of field-free molecular alignment by cross-defocusing assisted polarization spectroscopy.

We demonstrate the measurement of field-free molecular alignment of nitrogen by a cross-(de)focusing assisted polarization spectroscopy technique, allowing us to distinguish the transient orientation of prealigned molecules on the basis of the relative ratio of the adjacent revival peaks of the measured signal. For impulsive excitation with high pump intensities, the involved orientation-dependent ionization of the neutral molecules contributes to the signal.