Irradiating the HeNe laser on a disc rotating at low speed, the speed of each location on the rotating surface
was measured by analyzing images captured by a high speed camera. The Doppler shift, which was generated when the
laser light was mixed with the Doppler-shifted light scattering signal generated at each position when the laser light was
irradiated on the rotating surface, was acquired by a high-speed camera to store in a memory. After performing FFT for
stored measurements of each location, the Doppler-shifted value was converted to the rotational speed. The maximum
measurable rotational speed was determined depending on a frame speed of the camera, and the speed distribution of
the rotating surface was measured.