Frequency stabilization of a gas laser

The frequency of a gas laser was stabilized by making use of the competition between the oppositely circularly polarized components of a single cavity mode of a laser in an axial magnetic field. For appropriate transitions the coupling between the polarizations leads to a sharp crossover in their intensities as the cavity is tuned across the center of the atomic line. The difference of the intensities of the two polarizations is used as the discriminant for a feedback loop which keeps the cavity tuned to the atomic line center. This discriminant is at least an order of magnitude more sensitive than those previously reported. Two identical lasers and control systems were constructed utilizing the 1.52-microm transition of Ne (2s(2) ? 2p(1), J = 1 ? J = 0), and their relative stability was determined by measurements of their difference frequency. The very short term frequency fluctuations were essentially determined by the free-running stability of the laser and were of the order of +/-2 parts in 10(9) per laser. The longterm fluctuations were considerably reduced by the control loop, and over times of the order of 10 min, the average frequencies (10-sec averages) had standard deviations of 1 part in 10(10) per laser.