Large ring lasers: beyond the Macek and Davis experiment.

Large-scale ring laser gyroscopes are highly sensitive rotation sensors whose operating principle is based upon the Sagnac effect. They are constructed for direct measurement of Earth rotation and offer applications in geodesy, geophysics, seismology and tests of fundamental physics. Motivated by the fact that the scale factor of a ring laser gyroscope is dependent upon the operating wavelength as well as the geometric size; in this thesis, we report on the gyroscopic performance of PR-1, a vertically mounted 2.56 m2 ring laser gyroscope, operating on different neon transitions other than the standard 632.8 nm (3s2 → 2p4) helium-neon laser wavelength. State-of-the-art GaAs/AlGaAs crystalline coated, fused silica supermirrors have been employed to operate the laser on the 2s2 → 2p4 transition of neon at a wavelength of 1152.3 nm. The gyroscope is readily observed to unlock on Earth rotation, having a Sagnac beat note at approximately 60 Hz and demonstrated comparable performance to that achieved for operation with the industry standard ion beam sputtered (IBS) dielectric multilayer mirrors at 632.8 nm. Our results suggest a high potential for the implementation of crystalline coatings mirrors in the development of large-area ring laser gyroscopes along with other highly sensitive optical interferometric systems. Earth rotation sensing on the shortest helium-neon laser wavelength at 543.4 nm (3s2 → 2p10) was achieved by employing latest generation IBS mirrors that provide an extremely low transmission loss of 0.2 parts per million (ppm) at 543 nm, yielding a stable Sagnac frequency of 132.8 Hz. The gyroscope also exhibits frequency non-degenerate, bi-directional laser operation under the bias provided by Earth rotation while running on the 611.8 nm (3s2 → 2p6) of neon transition, having an operational Sagnac frequency of 117.2 Hz. Our initial assessment of operation at 543.4 nm suggests significant potential in improving the performance of ring laser gyroscopes especially for underground operations where the size of the laser will be limited by the laboratory space. Finally, we report on preliminary work towards the development of a cavity stabilisation scheme that employs two piezo-actuators acting on two diagonally opposite cavity mirrors to control the laser cavity perimeter. The feedback mechanism was achieved by operating the laser on multiple phase-locked longitudinal modes configuration, yielding a stable Sagnac beat frequency. The frequency difference between adjacent longitudinal modes is heterodyned with a reference frequency generated by a GPS-locked Radio Frequency (RF) generator, and the resulting beat note provides a feedback signal to the piezo-actuator controller. Using this method, the gyroscope achieved a frequency stability of 4.8 ×10−5 relative to Earth rotation, for over 100 s of averaging time