Simple laboratory demonstration of the Doppler shift of laser light

The edge of a smoothly rotating turntable was used as a reflecting surface in a Michelson interferometer configuration to demonstrate the Doppler effect on laser light. Attached to the edge of the turntable was reflective tape which greatly enhanced the backscattered light. Spectrum analysis of the detected signal indicated that all of the signal and noise components were contained in a frequency range of about 15% of the central Doppler frequency. As a quantitative test of the method, the wavelength of the laser source, known to be 633 nm, was measured to be (612±43) nm using an oscilloscope as the output device and (634±12) nm using a spectrum analyzer for the output. All components that were used with the exception of the spectrum analyzer are commonly available items. The techniques described in this paper provide a quantitative demonstration of the Doppler effect of light and overcome the usual problems caused by motional instabilities associated with the moving mirror.