Measurements of a mode-competition discriminant in a single-frequency argon ion ring laser

We have built a single-frequency argon ion ring laser using a coupled-cavity mode selector. Utilizing the gain asymmetry caused by the drift velocity imparted to the argon ions by the dc field used to excite the discharge, we have obtained a narrow discriminant centered on the argon laser line. This discriminant could be used to stabilize the laser to the center of the atomic line. We have measured discriminant widths of less than 200 MHz for the argon 4880-Å resonance line. The sensitivity of this discriminant is compared with other laser stabilization systems described in the literature, and it is shown that our system appears to be the most sensitive of the systems currently available for stabilizing the argon ion laser.