  We consider the polarization of thermal emission in the near-field of various
materials including dielectrics and metallic systems with resonant surface
modes. We find that at thermal equilibrium, the degree of polarization exhibits
spatial oscillations with a period of approximately half the optical
wavelength, independent of material composition. This result contrasts with
that of Setala, Kaivola and Friberg [Phys. Rev. Lett. 88, 123902 (2002)], who
find monotonic decay of the degree of polarization for systems in local thermal
equilibrium.
