An experiment to demonstrate the angular Doppler effect on laser light

Two simple and related experiments are outlined that allow the student to investigate the frequency shift experienced by a laser light beam when passing through a rotating half-wave retardation plate. The shift arises due to the energy exchange between a rotating optical element, in this case a half-wave plate, and a circularly polarized light beam. The shift is directly proportional to the rotation frequency of the optical element. The shift may be interpreted as an angular Doppler effect for light. (C) 1998 American Association of Physics Teachers.