A ring laser unlocked by the Earth's Sagnac effect has attained a frequency resolution of 1 part in 3 × 1021 and a rotational resolution of 300 prad. We discuss both theoretically and experimentally the sideband structure of the Earth rotation-induced spectral line induced in the microhertz–hertz region by frequency modulation associated with extra mechanical motion, such as seismic events. The relative sideband height is an absolute measure of the rotational amplitude of that Fourier component. An initial analysis is given of the ring laser record from the Arthur's Pass–Coleridge seismic event of 18 June 1994.
© 1995 Optical Society of America
Original Manuscript: April 19, 1994
Revised Manuscript: January 3, 1995
Published: August 20, 1995
G. E. Stedman, Z. Li, and H. R. Bilger, "Sideband analysis and seismic detection in a large ring laser," Appl. Opt. 34, 5375-5385 (1995)