Hi Everyone: I think some of you who familiar with quantum-optics know that the local photonic density of state can be calculated by the imaginary part of electromagnetic Green's function. The Green's function can be further presented by the dipole's mode pattern as G = E(r)*p0*ε(r)*c^2/ω^2 , where E(r) is the electric field profile, p0 is the dipole moment, ε is the dielectric function, ω is the frequency You can find these formulas in Lukas' book "Principle of nano-optics" However, I'm confused by the calculation's process. E(r) contain both the real and imaginary part, and so dose ε. Therefore, the final imaginary part of G will contain the cross-product item. The dielectric function will have a negative real part if there has metal material. But this will lead a negative imaginary part of Green's function in metal area, as also a "NEGATIVE DENSITY OF STATE"! Dose this reasonable?