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Photon Statistics and Spectra of Single Atom Lasers

Perry Rice, Bobby Jones**, and Shohini Ghose*

The basic model considered in this paper is a single atom inside an optical cavity. We consider both three- and four- level atomic systems and use incoherent pumping for both. We present numerical results the laser linewidth, and the second-order intensity correlation function, g(2) (t). These results are obtained using the quantum trajectory method, using the formalism of Carmichael. Previous work has shown that a single-atom laser is tenable if the atom-field coupling strength g is large enough. We have examined the behavior of such a device as b, the fraction of spontaneous emission into the laser cavity, is altered. It was found that for small b (< 0.1) the laser could be well described by a semiclassical theory with no amplitude squeezing and a well-defined threshold, while for larger values of b the fully quantum theory was needed.

In this work, we have used the quantum trajectory approach to investigate the linewidth of a single four-level atom laser, and compare our results with the results of the birth-death process and standard Scully-Lamb theory. We find that the linewidth can be significantly broader than the Schawlow-Townes limit, and that this width is related to the amount of amplitude squeezing.