Spectral line-shape measurement of an extremely weak amplitude-fluctuating light source by photon-counting-based second-order correlation spectroscopy

We demonstrate line-shape measurement of an extremely weak amplitude-fluctuating light source by using photon-counting-based second-order correlation spectroscopy combined with the heterodyne technique. The amplitude fluctuation of a finite bandwidth introduces a low-lying spectral structure in the line shape, and thus its effect can be isolated from that of the phase fluctuation. Our technique provides extreme sensitivity suited for single-atom-level applications. (c) 2006 Optical Society of America.