A quasi-continuous superradiant Raman laser with < 1 intracavity photon

¹ JILA, University of Colorado and NIST, and Dept. of Physics, University of Colorado, Boulder, Colorado 80309, USA
² Current Affiliation: Tech-X Corp., 5621 Arapahoe Ave. Ste. A, Boulder, Colorado 80303, USA

^a e-mail: jkt@jila.colorado.edu

Abstract

Steady-state collective emission from ensembles of laser cooled atoms has been proposed as a method for generating sub-millihertz linewidth optical lasers, with potential for broad impacts across science and technology. We have built a model system that tests key predictions for such active oscillators using a Raman laser with laser cooled atoms as the gain medium. The laser operates deep in the bad-cavity, or superradiant, regime of laser physics, where the cavity decay rate is much greater than the atomic coherence decay rate. Specifically, we demonstrate that a system of 10^6 87Rb atoms trapped in a 1D standing wave optical lattice can spontaneously synchronize and collectively emit a quasi-continuous coherent optical output, even when the intracavity field contains on average < 1 photon.