Radiative transfer with partial coherence in optically thick plasmas

A quantum transport model for atomic line radiation in plasmas is developed and analyzed. It is found that the Wigner phase space formulation of QED provides a consistent way to address the wave-particle duality in radiative transfer problems. If the photons' thermal de Broglie length is much smaller than all of the spatial scales of the problem under consideration (large-spectral-band limit), the radiation is not coherent and radiative transfer can be addressed with the usual treatments. In the general case, the Heisenberg uncertainty relation yields ambiguities in the description of the radiation-matter interaction mechanisms. We examine this issue and show that an accurate description of radiative transfer should involve a model with nonlocal interactions and requires an appropriate coarse-graining procedure. Calculations of transmission factors and absorption spectra in ideal cases are performed and indicate that significant misinterpretations can be made in spectroscopic diagnostics if the radiation coherence is not well accounted for. Applications to laser physics are also discussed.