Pulse Delay Time Statistics in a Superradiant Laser with Calcium Atoms

Cold samples of calcium atoms are prepared in the metastable P-3(1) state inside an optical cavity resonant with the narrow band (375 Hz) S-1(0) -> P-3(1), intercombination line at 657 nm. We observe a 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 P-3(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 S-1(0) -> P-3(1) transition should be extendable to allow for continuous wave laser operation.