Spontaneous down conversion of surface plasmon polaritons: strong-field   consideration
  A non-perturbative theory of the spontaneous down conversion (SDC) of surface plasmon polaritons at a metal-dielectric interface is presented. It is shown that the process is resonantly enhanced for the characteristic power of excitation, typically of the order of tens of watts. At a stronger excitation the yield of SDC decreases rapidly. At a stronger excitation the yield of SDC decreases rapidly. The reason for this decrease is the high rate of the change of surface plasmon polaritons by the laser field, exceeding the rate of the zero-point fluctuations responsible for the SDC process. The obtained results may help one to construct miniature sources of entangled photons for quantum communication. 
Vladimir Hizhnyakov and Ardi Loot
physics.optics quant-ph