  An investigation of field-free molecular alignment produced by elliptically
polarized laser pulses is reported. Experiments are conducted in CO$_2$ at room
temperature. A non invasive all-optical technique, based on the cross
defocusing of a probe pulse, is used to measure the alignment along two
orthogonal directions that is sufficient to provide a 3 dimensional
characterization. The field-free molecular alignment produced by a laser of
elliptical polarization is in good agreement in terms of amplitude and shape
with theoretical predictions. It turns out to be almost equivalent to the
superposition of the effects that one would obtain with two individual
cross-polarized pulses. The investigation highlights notably the occurrence of
field-free two-direction alignment alternation for a suitably chosen degree of
ellipticity. The analogy between this specific ellipticity and the well known
"magic angle" used in time resolved spectroscopy to prevent rotational
contributions is discussed.
