Scale-factor corrections in large ring lasers

The authors report on fluctuations of the geometric scale factor of a very large ring laser situated 30m underground in the Cashmere Cavern in Christchurch (New Zealand). Variations in temperature and atmospheric pressure cause thermoelastic deformations to the cavern, which lead to changes of the area and perimeter of the ring laser structure. In situ beam monitoring has been used to partially correct for these effects.