THERMAL-RADIATION AND AMPLIFIED SPONTANEOUS EMISSION FROM A RANDOM MEDIUM

We compute the statistics of thermal emission from systems in which th e radiation is scattered chaotically, by relating the photocount distr ibution to the scattering matrix-whose statistical properties are know n from random-matrix theory. We find that the super-Poissonian noise i s that of a blackbody with a reduced number of degrees of freedom. The general theory is applied to a disordered slab and to a chaotic cavit y, and is extended to include amplifying as well as absorbing systems. We predict an excess noise of amplified spontaneous emission in a ran dom laser below the laser threshold.