Prototype of a large ring laser for geoscientific applications

Optical ring cavities to measure rotation in geoscientific applications require quality factors 10/sup 10/10/sup 10/. The line center due to the Sagnac effect of the Earth rotation (about 70 Hz) has at present an error of about 5 /spl mu/Hz, i.e. a relative precision of 1.0/spl times/10/sup -20/ is achieved, using the 633 nm HeNe laser line.<>