An investigation of field-free molecular alignment produced by ellipticallypolarized laser pulses is reported. Experiments are conducted in CO$_2$ at roomtemperature. A non invasive all-optical technique, based on the crossdefocusing of a probe pulse, is used to measure the alignment along twoorthogonal directions that is sufficient to provide a 3 dimensionalcharacterization. The field-free molecular alignment produced by a laser ofelliptical polarization is in good agreement in terms of amplitude and shapewith theoretical predictions. It turns out to be almost equivalent to thesuperposition of the effects that one would obtain with two individualcross-polarized pulses. The investigation highlights notably the occurrence offield-free two-direction alignment alternation for a suitably chosen degree ofellipticity. The analogy between this specific ellipticity and the well known"magic angle" used in time resolved spectroscopy to prevent rotationalcontributions is discussed.
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