Analog of cosmological particle creation in electromagnetic waveguides

We consider an electromagnetic waveguide with a time-dependent propagation speed $v(t)$ as an analog for cosmological particle creation. In contrast to most previous studies which focus on the number of particles produced, we calculate the corresponding two-point correlation function. For a small step-like variation $\delta v(t)$, this correlator displays characteristic signatures of particle pair creation. As another potential advantage, this observable is of first order in the perturbation $\delta v(t)$, whereas the particle number is second order in $\delta v(t)$ and thus stronger suppressed for small $\delta v(t)$.