Ring Laser Gyro

A laser gyroscope or active Sagnac interferometer is a ring laser sitting on a rotating stage. The two counter-propagating laser waves have the same frequency when the table is at rest. As soon as it rotates, however, the finite velocity of light leads to different effective lengths of the ring cavity and, as a consequence, to slightly different optical frequencies of the waves. Their superposition then generates a beat note, whose frequency is proportional to the angular velocity of the table. A ring laser can, therefore, be used as a sensitive detector for rotations.

At low rotation speeds, the precision of the measurement is deteriorated by the so-called lock-in effect. The frequency of the beat note deviates from the theoretical value and can even become zero. The origin of this effect is a nonlinear coupling between the two counter-propagating waves caused by light scattering at the mirror surfaces.

Our goal is to find ways of minimizing the lock-in effect.