Oscillations, Waves, and Interactions - GWDG

Oscillations, Waves and Interactions, pp. 279–310
edited by T. Kurz, U. Parlitz, and U. Kaatze
Universitätsverlag Göttingen (2007) ISBN 978–3–938616–96–3
urn:nbn:de:gbv:7-verlag-1-11-4
High-resolution Sagnac interferometry
K. U. Schreiber
Technische Universität München, Forschungseinrichtung Satellitengeodäsie,
Fundamentalstation Wettzell, 93444 Bad Kötzting
Email: ulrich.schreiber@bv.tum.de
Abstract. Ring lasers are the most important sensors for the measurement of rotation
when it comes to high stability and high sensor resolution. Their scale factor and hence their
sensitivity increases with the area enclosed by two counter-propagating laser beams. Over
the last decade a number of extremely large ring lasers were built, improving the sensitivity
and stability of the measured rotation rate by several orders of magnitude over previous
commercial developments. This progress has opened the door for entirely new applications
of ring laser gyroscopes in the fields of geophysics, geodesy and seismology. Ring lasers for
example are currently the only viable measurement technology, which is directly referenced
to the instantaneous rotation axis of the Earth. This document reviews the research carried
out by our international working group over the last decade and describes the current state
of the large-scale ring laser technology.
1 Introduction
Highly sensitive rotation sensors have many applications. They reach from applications
in robotics over navigation up to high-resolution measurements in seismology,
geodesy and geophysics. The field of these applications is very broad and therefore a
wide range of different sensor types and specifications exists to satisfy these demands.
In order to understand the importance of rotation sensors one should keep in mind
that there are in total six degrees of freedom of movement, three for translations
and three for rotations, respectively. While the measurements of translation are
usually based on the determination of accelerations relative to an inertial test mass,
rotations can be established either by mechanical gyroscopes or they can be measured
absolutely by exploiting the Sagnac effect. Today fibre-optic gyros are the most
prominent representatives for passive optical Sagnac interferometers, while ring laser
gyroscopes represent the group of active Sagnac devices. They characterize the most
sensitive and most stable class of gyroscopic devices.
2 History of Sagnac interferometers
In 1881 A. Michelson set up an L-shaped optical interferometer and showed subsequently
that no ether could exist, provided the ether is assumed to be at rest and is