The Sagnac effect

A revived interest in the Sagnac effect, because of its navigational potentialities has recently resulted from the development of the self-oscillating laser version of the original Sagnac interferometer. Where the Sagnac interferometer or ring laser is an example of an electromagnetic sensor of absolute rotation, it was believed that some historical and theoretical background information might be useful in exploring and further evaluating the possibilities of electromagnetic sensing of absolute rotation. A critical literature study of the many experimental ramifications and the older kinematical theory of the effect is presented. This geometric optical theory is then complemented and compared with more recent work that is based on a physical optical analysis using a complete electromagnetic description of the phenomenon. (Author).