Oscillations, Waves, and Interactions - GWDG

282 Schreiber
These properties made them very welcome for applications in navigation. Compact
designs, made monolithically from blocks of Zerodur, were used to make ring lasers
of an area around 0.01 m 2 . They are widely used in aircrafts [6]. The sensitivity of a
ring laser gyroscope mostly depends on the scaling factor, i. e. the ratio of the area
and the perimeter. Today, 80 years after the outstanding experiment of Michelson
and Gale, a number of gyroscopes have been built, which exceed the performance
of the historic instrument by approximately two million, while the corresponding
sensors are a lot smaller at the same time. This does not only allow one to measure
the rotation rate of the Earth ΩE, but it also readily shows small variations of this
quantity. Apart from a response of the Earth to external forces, these fluctuations are
resulting from a momentum exchange between the atmosphere, the hydrosphere and
the lithosphere. Therefore perturbations of Earth rotation can be used as an indirect
indicator for the monitoring of global phenomena, such as variations in global ocean
circulation.
4 Ring laser design
Atmosphere and hydrosphere make up a very small portion of the entire Earth mass
only. Therefore an extremely high resolution for any type of gyroscope is required to
access the information contained in these geophysical signals at a level of well below
10 −7 . Apart from the actual sensitivity of the gyro also a remarkable sensor stability
is required. Some known periodic signals, such as the Chandler wobble, have periods
of around 432 days. Other such small-scale signals of interest are expected to be
aperiodic and one would wish to distinguish them clearly from sensor drifts. In order
to provide the required sensor stability it is desirable to make them mechanically as
rigid as possible. Furthermore the shape must not be affected by ambient temperature
and atmospheric pressure changes.
Figure 2. The C-II ring laser at the time of construction at Carl Zeiss (Oberkochen) at
the end of the year 1996. Photograph courtesy of Carl Zeiss GmbH, Oberkochen.