Probing the Purcell effect without radiative decay: lessons in the frequency and time domains

The effect of cavities or plates upon the electromagnetic quantum vacuum are considered in the context of electro-optic sampling (EOS), revealing how they can be directly studied. These modifications are at the heart of e.g. the Casimir force or the Purcell effect such that a link between EOS of the quantum vacuum and environment-induced vacuum effects is forged. Furthermore, we discuss the microscopic processes underlying EOS of quantum-vacuum fluctuations, leading to an interpretation of these experiments in terms of exchange of virtual photons. With this in mind it is shown how one can reveal the dynamics of vacuum fluctuations by resolving them in the frequency and time domains using EOS experiments.