Intensity Correlations of a Cooperative System

We suggest that the intensity correlation function could be an important tool in the study of atomic cooperative behavior because it contains predominantly components at 0, $\pm 4\Omega$ in the limit of large Rabi frequency ($2\Omega$) and large cooperation number. This is in contrast with the single-atom prediction where the intensity correlation function contains only frequency components at 0, $\pm 2\Omega$. The master equation for the collective system is solved analytically in the secular approximation.