MEASURING THE QUANTUM-LIMITED LINEWIDTH OF A LASER BY USING THE ZEEMAN-EFFECT

We explore Zeeman operation of a laser as a way to measure its quantum phase noise, We measure the differential phase diffusion of a sigma() and a sigma(-) mode; the degeneracy of these modes is lifted by a lo ngitudinal magnetic field, Experiments are performed on a high-gain He Xe gas laser, comparing quantum linewidths measured using this techniq ue with measurements on the same laser using the well-established self -heterodyne technique, The two methods are found to be equivalent when the magnetic field used in the Zeeman technique is sufficiently large , The advantages of the Zeeman technique as compared to the self-heter odyne technique are its extreme simplicity and very modest laser-power requirement.