  The quantization of a real massless scalar field in a spacetime produced in a
collision of two electromagnetic plane waves with constant wave fronts is
considered. The background geometry in the interaction region, the
Bell-Szekeres solution, is locally isometric to the conformally flat
Bertotti-Robinson universe filled with a uniform electric field. It is shown
that before the waves interact the Bogoliubov coefficients relating different
observers are trivial and no vacuum polarization takes place. In the non-
singular interaction region neutral scalar particles are produced with number
of created particles and spectrum typical of gravitational wave collision.
