Coherence Properties of Blackbody Radiation. I. Correlation Tensors of the Classical Field

This paper is concerned with the extension of some recently reported results, especially those of Bourret (1960), relating to coherence properties of blackbody radiation. An explicit expression for the complex electric correlation tensor ${\mathcal{E}}_{\mathrm{ij}}(\mathrm{r}, \tau )$ of blackbody radiation is derived, and on the basis of it spatial coherence ($\tau =0\mathrm{}$) is discussed in detail. The behavior of diagonal as well as nondiagonal components is illustrated by contour diagrams. In particular, it is found that the nondiagonal components of the correlation tensor, even though being zero for zero-space separation (r=0), acquire, in general, nonvanishing values when r ≠ 0. The magnetic and mixed correlation tensors are also discussed.