Self-Organization, Broken Symmetry, and Lasing in an Atomic Vapor: The Interdependence of Gratings and Gain

We describe a novel optical gain mechanism observed in a strongly driven Doppler-broadened atomic vapor. Gain and self-stabilizing laser oscillations are observed in a direction which is counterpropagating with respect to the traveling wave pump. Using Bragg diffraction, we show that the underlying gain-lasing mechanism is directly tied to a spontaneously formed optical wavelength grating. We suggest that this grating arises from a self-organization or self-bunching of the atoms, an effect which is mediated by recoil just as in the free electron laser.