Experimental and Theoretical Studies of Bifurcations by Measuring the Optical Spectrum of a Ring Laser

We have conducted careful measurements of the changes in the output of a single-mode, inhomogeneously-broadened, unidirectional ring laser as the excitation and cavity detuning are varied. We are able to track the splitting of the optical spectrum as the laser makes a transition from stable cw operation to pulsed operation by heterodyning the laser output with a stabilized reference laser. For a resonantly tuned cavity, we see that with increasing excitation the laser makes an abrupt transition from a single optical carrier wave to two equally strong components in the optical spectrum. The splitting between these two components increases with increasing excitation above the instability threshold.