History Of The Laser Gyro

The ring laser gyro had its beginning with the observation that rotation removed the degeneracy between the clockwise and the counterclockwise traveling waves in a resonant cavity, and that the frequency difference was directly proportional to the angular rotation rate l. The measurement of rotation by the interference of electromagnetic waves in non-resonant or non-reentrant structures was recognized more than a half century earlier in 1897 by Oliver Lodge2. His research apparatus which is shown in Figure 1 consisted of mirrors at the corners of a 1 m x 6 m rectangle, light source, semi-transparent plate, and telescope, and was used in his study of the drag of the ether by rotating steel discs. In his negative comments concerning ether drag, he included the following comment. "Hence if, --, the whole apparatus, lantern, optical frame, telescope, observer and all were mounted on a turntable and caused to rotate, a reversible shift of the bands should be seen. ----The effect would be of an aberrational kind, the opposite light beams being accelerated and retarded by the motion appropriately.----My present optical apparatus mounted on a turntable revolving 4 times a minute should show something, viz.: 1/100th band shift each way. A certain amount of discomfort during the accelerative stages of any speed could hardly be avoided, and even