Dynamical Casimir effect for surface plasmon polaritons
  Emission of photon pairs by an interface of asymmetric dielectric and thin metal film excited by a normally falling plane wave is considered. The excitation causes oscillations in time of the phase velocity of surface plasmon polaritons in the interface. This leads to the dynamical Casimir effect - the generation of pairs of surface plasmon polariton quanta, which transfer to photons outside the interface. In case of a properly chosen interface, the yield of two-photon emission may exceed that of usual spontaneous parametric down conversion. 
V. Hizhnyakov, A. Loot, S. Ch. Azizabadi
cond-mat.mes-hall cond-mat.mtrl-sci physics.optics