New Applications of very large Ring Lasers

摘要

Very large ring lasers have been constructed to monitor small variations of Earth rotation. After more than a decade of research, rings with areas of up to 367 square meters are outperforming gyros for navigation by several orders of magnitude. As a consequence periodic geophysical signals with periods around one day and half a day have become visible in the time-series of ring laser observations. These signals are introduced by variations in the orientation of the ring laser plane and currently limit the uncorrected sensor resolution to 2 parts in 10{sup}8 with respect to the Earth rotation rate. Sensor sensitivity however is not the only criterion for ring laser operation. Long term bias and area stability are critical demands for rotation sensors applied to the field of geophysics. In particular on ring lasers with an area of 367 square meters area strain is not negligible. Operating a large ring laser in split mode, that is on one single mode per sense of rotation with different longitudinal index, gives access to the quantity of area strain. In this talk we also compare the currently achieved performance of 3 of our rings with different size. Since large ring lasers are also sensitive to seismic signals, the data logging procedure was changed to allow the measurement of rotational velocities at rates of more than 5 Hz. The recent earthquake in France of Feb. 22, 2003 was successfully recorded with this new logging scheme which we consider a key technology for the GEOSENSOR, a hybrid system for the introduction of rotation measurement to seismic applications.