Electromagnetic vacuum energy for two parallel slabs in terms of   surface, wave guide and photonic modes
  The formulation of the Lifshitz formula in terms of real frequencies is reconsidered for half spaces described by the plasma model. It is shown that besides the surface modes (for the TM polarization), and the photonic modes, also waveguide modes must be considered. 
M. Bordag
quant-ph math-ph math.MP physics.plasm-ph