2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/91180A two-photon emission of a medium with periodically time-dependent refractive index is considered. The emission results from the zero-point fluctuations of the medium. Usually this emission is very weak. However, it can be strongly enhanced if the resonant condition $ω_0$ = 2.94 $c/l_0$ is fulfilled (here $ω_0$ and $l_0 $ are the frequency and the amplitude of the oscillations of the optical length of the medium, respectively). Besides, a medium with resonant oscillations of the optical length performs the phase conjugated reflection with high efficiency. A similar resonant enhancement of the two-quantum emission of other bosons is also predicted.7 pages, two figuresQuantum Physicstext