Laser-based deflection measuring method and apparatus

摘要

A laser beam is passed through a naturally birefringent or optically active device contained within the laser cavity. The device is oriented so that its optical axis is parallel to the laser beam, thus producing no birefringence or optical activity in the cavity in the steady state. The slightest tilting of the birefringent, or optically active, element causes significant changes in the modes of excitation of the optical cavity which are detected by a photosensitive beat detector. Thus the deflection angle of the optical axis is measured directly in terms of a beat frequency. By combining Faraday or Fresnel-Fizeau effects with optical activity, quadrature mode operation of a ring-laser embodiment is achieved, and is used to improve signal stability and noise rejection.