Frequency-independent effective rest mass of photons in the 2TDLM model

A physically interesting {\it effective rest mass} of photons in electromagnetic media, which is independent of wave frequency $\omega$, is defined in the present paper. It is verified that this frequency-independent effective rest mass of photons can be easily read off from the optical refractive index squared $n^{2}(\omega) $ of commonly-seen electromagnetic media. As an illustrative example, we extract the frequency-independent effective rest mass of photons from $n^{2}(\omega) $ in the {\it two time derivative Lorentz material} (2TDLM) model. The connection between effective rest mass and electromagnetic parameters of electric permittivity ($\epsilon $) and magnetic permeability ($\mu $) in left-handed media is also briefly discussed.