Gyroscopic performance and some seismic measurements made with a 10 meter perimeter ring laser gyro housed in the Ernest Rutherford building

We describe the construction and operation of a large ring laser whose beam paths enclose an area of 6.25 m². The gyroscopic performance of this large laser interferometer was determined using laser operation at a wavelength of 632.8 nm. The laser cavity Q was inferred to be 1.1 × 10¹² via a measured ring-down time of 375 µs, and the measured Sagnac frequency is 198.40 Hz due to Earth’s rotation. The measured experimental sensitivity to rotation achieved is 7.9 × 10⁻¹² rad/s/^√Hz at an averaging interval of 512 s (being limited primarily by ambient building noise). The observation of microseismic activity in the 200 mHz region as well as local earthquakes is discussed.