A Sagnac experiment with electron waves in vacuum is reported. The phase shift caused by rotation of an electron biprism interferometer placed on a turntable has been measured. It was found to agree with prediction within error margins of about 30 %. A compact ruggedized electron interferometer of novel design was used. It is based on a high precision optical bench of 36 cm length. This interferometer is less sensitive to mechanical vibrations and electromagnetic stray fields than conventional electron interferometers by orders of magnitude. A low energy (150--3000 eV) electron beam emitted by a field emission electron source was used. For the most part, electrostatic electron optical components were employed. The magnified interference fringe pattern was intensified by a dual stage multi-channel plate intensifier, recorded by a charge-coupled device (CCD) video camera, transmitted from the turntable to the laboratory system via a slip ring, and evaluated by an image processing system. Both the rotation rate and the area enclosed between the two partial waves were varied (up to values of 0.5 sec exp-1 and 3.9 mm exp2, resp.). Fringe shifts on the order of 5 % of a fringe period were attained. Some historical aspects of the Sagnac effect as well as some aspects of its interpretation are mentioned. A brief informal discussion is included of the interpretation of the Sagnac phase shift as a geometric phase (``Berry phase'') caused by the global anholonomy of the local phase factor that is produced by the gauge field induced by rotation.
For more information about experiments with electrons click here.
For more information about the interferometry group click here.