optical lever
optical lever
[′äp·tə·kəl ′lev·ər] (optics)
A device for measuring small angular displacements of a rotating body in which a narrow fixed beam of light is directed onto a small mirror attached to the body and the reflected beam is directed onto a screen, producing a spot of light whose position is measured.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.