Fringe Contrast characterization and optimization for Ring Laser Gyroscopes

Top sensitivity Ring Laser Gyroscopes based on a simple mechanical scheme, so called heterolithic, have shown to operate on a continuous basis; since the mirror positions are not fixed, unwanted signals can occur, and data selection is necessary. For this purpose, Fringe Contrast is very useful. It depends on output beams intensity, alignment, and polarization; the model of the alignment and polarization contributions to Contrast has been implemented, and tested on the GP2 prototype. Polarization changes are corrected by acting on the output beams with plates, in order to recombine linearly polarized light. Using such model, the GP2 prototype was characterized as for polarization of the beams, inside the cavity and at their interference, and for non-planarity; as a result, the interfering beams off-axis has also been measured.