  A substantial increase in local laser intensity is observed in the near field
behind a plasma shutter.This increase is caused by the interference of the
diffracted light at the relativistic plasma aperture and it is studied both
analytically and using numerical simulations. This effect is only accessible in
the regime of relativistically induced transparency and thus it requires a
careful choice of laser and target parameters. The theoretical estimates for
the maximum field strength and its spatial location as a function of target and
laser parameters are provided and compared with simulation results. Our full 3D
Particle-in-Cell simulations indicate that the laser intensity may be increased
roughly by an order of magnitude improving the feasibility of strong field QED
research with the present generation of lasers.
