An active ring laser gyroscope is a highly sensitive interferometer for the direct measurement of instantaneous inertial rotation via the optical beats generated from two frequency-shifted beams counterpropagating along a common enclosed path. In this thesis, the two He-Ne gas lasers called ’Physics Ring 1’ (PR-1) and ’Ernest Rutherford 1’ (ER-1) are utilised as large ring laser gyroscopes. They are designed for applications in the geosciences and civil engineering field as well as for tests of fundamental physics.

The research presented in this thesis focuses on several possible schemes for improving gyroscopic performance regarding rotational sensitivity and long-term stability. Feasible techniques include geometrical-upscaling of the ring cavity, the use of higher optical frequencies, implementation of a perimeter stabilisation system, and correction of systematic errors were utilised to maximise the useful resolution of the ring laser gyros.

A multi-wavelength laser gyro that can operate at 611.8, 604.6, and 593.9 nm has been developed. The initial results predict that simultaneous stable operation on multiple neon transitions having dissimilar gains is achievable when the intra-cavity supermirrors provide appropriate, unequal loss for each wavelength output. The success of stable multi-wavelength operation would ultimately benefit schemes for systematic calibration of dispersion-induced null-shift errors. In particular, the 611.8 nm laser yielded stable optical beats having frequencies of about 117.4 Hz due to the Earth rotation and obtained a usable resolution of 8.8 nrad/s (1.2 10−4ΩE, where ΩE is the Earth’s rotation rate of 7.2921159 10−5 rad/s) for an optimised gas fill and a cavity Q of 1.2 1011. Furthermore, the 2.56 m2 PR-1 laser has been configured with commercially sourced standard laser mirrors to operate at 1152.3 nm. The outcome demonstrates that this rotational sensor can unlock on Earth’s rotation.

A new ring laser (denoted as ER-1) having a perimeter of 10 m and beam paths which enclose an area of 6.25 m2 has been developed and used to demonstrate sensor functionality using operation on three different neon transitions in the visible region. It is found that the 632.8, 611.8, and 543.4 nm operating wavelengths can offer the highest rotational resolutions of 36 prad/s (4.9 10−7ΩE), 80 prad/s (1.1 10−6ΩE), and 226 prad/s (3.1 10−6ΩE) respectively in Earth rotation measurement. Various excitation systems (gain tube, RF transmitter) and mirror configurations have been applied and compared to identify the optimal operational conditions for frequency-upscaled gyroscopic operation. The average sensor resolution of ER-1 is two orders of magnitude higher than that of PR-1. The critical factor which accounts for this improvement is the increase in the cavity size and geometric stability.

Other significant measurements using ER-1 include the successful detection of marine microseisms and precise measurement of earthquake-induced ground rotational motions. The ocean-generated microseismic signals observed were in the 150 - 250 mHz frequency band. Two earthquakes (epicentres at a similar distance to the ER-1 site) of different magnitudes (M) at 5.4 and 5.8 have generated the highest local ground rotation rate at 78 and 254 nrad/s, respectively. The phase velocities for the S-waves and Love waves inferred from the observation were calculated at about 4.3 km/s and 3.4 km/s, respectively. These measured values fit into the expected range provided by common seismology.