2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/187098We use an analytic form for the Heisenberg-Euler Lagrangian to calculate the birefringent and dichroic properties of the vacuum for arbitrarily strong wrenchless fields. PACS : 12.20.Ds, 42.25.Lc 97.60.Jd, 98.70.Rz8 pages, 2 figures, to appear in Journal of Physics AHigh Energy Physics - PhenomenologyAstrophysicstext