Optical path length modulator

摘要

An optical path-length modulator which comprises a tube having at one open end a lens of which the focal length is equal to the distance between this lens and the surface of a concave mirror which is disposed at the closed end of the tube and which has a radius of curvature equal to the focal length of the lens. The tube is carried between and mounted on two spaced apart diaphragms which can flex in order that the tube may move axially. The tube constitutes an armature for an electromagnetic vibrator which includes also pole pieces surrounding the tube and a driving coil on one of the pole pieces. Energization of the driving coil causes to and fro axial movement of the tube. Collimated light entering the tube via the lens is brought to a focus at the surface of the mirror and is rereflected the way it entered.