Abstract
We review the current status of large ring laser gyroscopes having the potential to contribute to terrestrial measurements of general relativistic precessions. At this point in time, although these devices possess the raw sensitivity for such a measurement, they remain limited by long-term geometric instability, detection noise and imperfections in the physical models required to isolate geophysical effects. Furthermore, minute non-reciprocal biases provide a null-shift error and therefore no currently constructed laser system meets the requirement of absolute rotation rate sensing. Nevertheless, we are of the view that these are surmountable problems and the ability of ring laser gyroscopes to measure low frequency to DC signals has vastly increased in the last decade.
Highlights
Gyroscopic measurement of general relativistic precessions has long been proposed; it was never a realistic prospect until the advent of satellite technology [1], which, inspired the GravityProbe B experiment [2]
The Gravity Probe B experiment was a great success albeit that the science outcome with an error margin of 19% was not as definitive as one might have hoped
The mechanical gyros of Gravity Probe B placed in a μ-g environment of a near earth orbit at cryogenic temperatures performed at a remarkable drift rate of ωd < 3.2 × 10−11 ◦ /h
Summary
Gyroscopic measurement of general relativistic precessions has long been proposed; it was never a realistic prospect until the advent of satellite technology [1], which, inspired the Gravity. Ring laser gyroscopes capable of measuring Earth rotation came much later [8] and over the last twenty-five years have increased in size between 1 and 834 m2 [9]; more recently, these have employed short wavelength neon transitions in order to maximise the scale factor of the device via the optical frequency [10]. For quite practical reasons, large laser gyroscopes fall into two classes of construction; those having a heterolithic stainless steel design and those which are monolithic mechanical structures made from Zerodur This determines the usable sensitivity of a device of any particular geometric size; and so it is that the four by four metre G-ring [11] yields the highest usable sensitivity via its stability [12,13]. The unambiguous measurement of the Lense–Thirring effect requires a sensor capable of absolute rotation rate sensing [16] and this cannot be said to have been fully realised
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