Observation of the rotational Doppler effect for optical beams with helical wave front using spiral zone plate

A rotating spiral zone plate was used to implement and measure the rotational Doppler effect for plane-polarized optical beams with helical wave front (optical vortices). The frequency shift was analyzed in terms of energy exchange between the beams and moving optical elements. (C) 2002 MAIK Nauka/Interperiodica.