  The relationship between thermal light and coherent pulses is of fundamental
and practical interest. We now know that thermal light cannot be represented as
a statistical mixture of single pulses. In this paper we ask whether or not
thermal light can be represented as a statistical mixture of sets of pulses. We
consider thermal light in a one-dimensional wave-guide, and find a convex
decomposition into products of orthonormal coherent states of localized,
nonmonochromatic modes.
