  The transition between a Minkowski space region and a parity breaking medium
domain is thoroughly discussed. The requirement of continuity of the field
operator content across the separating boundary of the two domains leads to
Bogolyubov transformations, squeezed pairs states and squeeze operators that
turn out to generate a functional SU(2) algebra. According to this algebraic
approach, the reflection and transmission probability amplitude across the
separating boundary are computed. The probability rate of the emission or
absorption of squeezed pairs out of the vacuum (generalization of the
Sauter-Schwinger-Nikishov formula) is obtained.
