2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/185670We consider the photon field between an unusual configuration of infinite parallel plates: a perfectly conducting plate $(ε\to\infty)$ and an infinitely permeable one $μ\to\infty)$. After quantizing the vector potential in the Coulomb gauge, we obtain explicit expressions for the vacuum expectation values of field operators of the form $<{\hat E}_i{\hat E}_j>_0$ and $<{\hat B}_i{\hat B}_j>_0$. These field correlators allow us to reobtain the Casimir effect for this set up and to discuss the light velocity shift caused by the presence of plates (Scharnhorst effect \cite{Scharnhorst,Barton,BarScharn}) for both scalar and spinor QED.Latex, 16 pages, no figuresHigh Energy Physics - Theorytext