  Laser-based searches of the yet unobserved vacuum birefringence might be
sensitive for very light hypothetical particles carrying a tiny fraction of the
electron charge. We show that, with the help of contemporary techniques,
polarimetric investigations driven by an optical laser pulse of moderate
intensity might allow for excluding regions of the parameter space of these
particle candidates which have not been discarded so far by laboratory
measurement data. Particular attention is paid to the role of a Gaussian wave
profile. It is argued that, at energy regimes in which the vacuum becomes
dichroic due to these minicharges, the transmission probability of a probe beam
through an analyzer set crossed to the initial polarization direction will
depend on both the induced ellipticity as well as the rotation of the initial
polarization plane. The weak and strong field regimes, relative to the
attributes of these minicharged particles, and the relevance of the
polarization of the strong field are investigated.
