Mar 15 – 18, 2011
Europe/Rome timezone

An array of ring-lasers to measure the Frame Dragging of the Earth

Mar 16, 2011, 7:46 PM


Angela Di Virgilio (INFN, Pisa)


It has been well known for many years that ring lasers, angular velocity inertial sensors, can be used to measure the Frame Dragging (Lense-Thirring effect) of the Earth provided that the sensor drift can be controlled sufficiently. The ring Laser G in Wettzell (Germany) has shown that a sensitivity of 20nrad/s/sqrt(Hz) can be achieved routinely. Both, sensitivity and accuracy improvements are expected in the near future due to tighter control loops on the system and improvements in mirror making. The 3 groups (NewZealand, Germany and Italy) who work on this kind of devices, have been sharing their experience in order to improve the instrument as much as possible. As a result of this joint effort a new prototype ring will be built in NewZealand in 2011. The Italian group runs the middle size ring G-Pisa, which operates in the central area of Virgo gravitational waves antenna at the moment . Based on the results of G, we have worked out that a system of 6 large gyros will be able to reconstruct the Lense-Thirring effect with a precision of at least 10% in about a month of integration. Improvements in the accuracy of the device would improve the results and 1% of accuracy seems feasible with measurements summing over a few years. Essential for our test is the comparison with the Earth angular rotation as provided by the IERS. In order to reach this ambitious goal, our project requires the construction of a sensor of 2 components, each consisting of two parallel ring lasers, collocated, and oriented along two different axis of orientation, making 4 rings in total. Each ring will be built using the economic modular design, pioneered in the GEOSENSOR project. It is actively controlled using a servo system. The perimeter will be around 24 m, and the geometry should be close to a square with an accuracy of the order of 1 part in 105. We plan to install and test our system in an underground laboratory, such us Laboratori Nazionali del GranSasso (LNGS), in order to reduce the top soil perturbations seen in our other sensors and to achieve very high thermal stability. Beyond fundamental physics, this experiment would be very important for geodesy and geophysics.

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