Electromagnetic field correlations near a surface with a nonlocal optical response
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- Henkel, C. & Joulain, K. Appl. Phys. B (2006) 84: 61. doi:10.1007/s00340-006-2219-9
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The coherence length of the thermal electromagnetic field near a planar surface has a minimum value related to the nonlocal dielectric response of the material. We perform two model calculations of the electric energy density and the field’s degree of spatial coherence. Above a polar crystal, the lattice constant gives the minimum coherence length. It also gives the upper limit to the near field energy density, cutting off its 1/z3 divergence. Near an electron plasma described by the semiclassical Lindhard dielectric function, the corresponding length scale is fixed by plasma screening to the Thomas–Fermi length. The electron mean free path, however, sets a larger scale where significant deviations from the local description are visible.