  Elastic scattering of laser radiation due to vacuum polarization by spatially
modulated strong electromagnetic fields is considered. The Bragg interference
arising at a specific impinging direction of the probe wave concentrates the
scattered light in specular directions. The interference maxima are enhanced
with respect to the usual vacuum polarization effect proportional to the square
of the number of modulation periods within the interaction region. The Bragg
scattering can be employed to detect the vacuum polarization effect in a setup
of multiple crossed super-strong laser beams with parameters envisaged in the
future Extreme Light Infrastructure.
