Design and initial operation of a 367-m²rectangular ring laser

The design and operation of a proof-of-principle rectangular He–Ne ring laser resonator with a cavity perimeter of 77.0 m and an area of 367 m²are described. With unevacuated beam lines this device gave an Earth-induced Sagnac frequency of 1513 Hz, with a relative Allan deviation over 1000 s down to 3 parts per million. The Earth’s rotation provided a bias that eliminated the lock-in susceptibility. The use of increased pressure in the plasma tube facilitated single-mode operation by increasing the homogeneous pressure-broadened linewidth.