Speed measurement of a rotating diffuser by means of the Doppler shift of the scattered light

G. G. ROMERO; E. E. ALANÍS; A. C. MONALDI; H. J. RABAL

Lat. Am. J. Phys. Educ.

Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada del Instituto Politécnico Nacional and the Latin American Physics Education Network.

Año: 2011 vol. 5 p. 423 - 427

1870-9095

An experiment designed to detect the Doppler shift frequency of light scattered by a moving diffuser when the speed of the scatters has a component in the line of sight direction is described. The device proposed is similar to a Michelson interferometer, in which the mirrors have been replaced by two diffuse surfaces, one of them moving with constant angular speed, while the other remaining at rest. The coherent superposition of the light dispersed in both surfaces results in a dynamic speckle pattern, whose intensity fluctuation contains the beat frequency between the component frequencies. The intensity fluctuations are recorded by means of a photodetector which signal is digitized with a sound interface of a PC multimedia system. The spectral distribution of the signals shows peaks centered in the corresponding beating frequency of the light dispersed by the moving diffuser. These frequencies are correlated with the tangential speed of the diffuser at several distances from the axis of rotation.