RING LASER

摘要

A ring laser (10) incorporates a laser rod (R) with end faces (R1, R2). The first face (R1) is coated for high reflectivity at the laser wavelength and the second (R2) for high transmission at this wavelength. The first face (R1) provides one cavity end mirror, and a concave mirror (M1) spaced apart from the rod (R) provides the other. A rhombic prism (P) between the rod (R) and mirror (M1) defines differing (figure of eight) forward and return paths (14 to 17, 18 to 21) for cavity radiation passing from one end mirror (R1 or M1) to the other and returning. The prism (P) presents Brewster's angle refracting surfaces. The second rod face (R2) is tilted to produce an optical path in two planes. A magnetic field (B) along the rod axis (Ra) produces Faraday rotation of polarization. This counteracts rotation arising from non-coplanar optics for one direction of propagation around the laser cavity (10) but not the other. This produces unidirectional laser action.