Abstract
Large frame optical Sagnac gyroscopes, more commonly called ring laser gyroscopes, are considered the only device able to provide fast and very high sensitivity measurement of the length of the day (LOD), and of the Earth rotation axis variations. Several large frame Sagnac gyros are presently operative with high duty cycle and sensitivity well below fractions of nrad/s in 1 second measurement. At present other inertial angular rotation sensors are not competitive with ring laser gyroscopes. The feasibility depends on the so called hetero-lithic ring lasers. The present status of art is reported, and the feasibility of the main goals for geodesy discussed.
Highlights
More than 100 years ago, the French physicist Georges Sagnac, in his research aimed at the discovery of the ether, found an effect of special relativity: the interference of two beams counter-propagating in a closed path attached to a frame is proportional to the rigid rotation of the frame (Sagnac, 1913a,b; Post, 1967)
GINGERINO is operative on a continuous basis unattended and free running with 95% duty cycle and sensitivity better than fractions of nrad/s in 1 s measurement
This analysis has shown that the orientation of the apparatus of GINGERINO is stable at the level of μrad, indicating that the Gram Sasso laboratory it a good location for the installation of a RLG at the maximum signal
Summary
More than 100 years ago, the French physicist Georges Sagnac, in his research aimed at the discovery of the ether, found an effect of special relativity ( usually referred to as the Sagnac effect): the interference of two beams counter-propagating in a closed path attached to a frame is proportional to the rigid rotation of the frame (Sagnac, 1913a,b; Post, 1967). The family of inertial angular rotation sensors based on the Sagnac effect (SG) is rather large. These can be based on atoms or light; if the latter, there are devices based on optical fibers (FOG) and others based on resonant ring cavities. This last group is further divided in two: passive ring cavity (PRC) and active ring cavity, called ring laser gyro (ARC or RLG). PRC and RLG are based on the same apparatus: in one case the laser light is injected from the outside, while the other contains an active medium and operates as a laser with two counterpropagating modes. General Relativity is necessary to fully describe the Sagnac effect and, for that we refer to, the work of Tartaglia et al
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