We find theoretically that an incident laser beam with a diverging (converg
ing) profile on the vacuum-plasma boundary turns out a converging (divergin
g) beam in the plasma when epsilon (3) < 0 as if there were a convex (conca
ve) lens at the boundary, <epsilon>(3) being the dielectric coefficient alo
ng the magnetic field. (C) 2001 Elsevier Science B.V. All rights reserved.