Pulse delay time statistics in a superradiant laser with calcium atoms

Cold samples of calcium atoms are prepared in the metastable ${}^3$P${}_1$ state inside an optical cavity resonant with the narrow band (375 Hz) ${}^1$S${}_0{\to }^3$P${}_1$ intercombination line at 657 nm. We observe superradiant emission of hyperbolic secant shaped pulses into the cavity with an intensity proportional to the square of the atom number, a duration much shorter than the natural lifetime of the ${}^3$P${}_1$ state, and a delay time fluctuating from shot to shot in excellent agreement with theoretical predictions. Our incoherent pumping scheme to produce inversion on the ${}^1$S${}_0{\to }^3$P${}_1$ transition should be extendable to allow for continuous wave laser operation.