Abstract
The scattering monochromatic light from a rough surface produces a speckle pattern. The speckle pattern from a moving rough surface is detected by a one-dimensional photo-diode array in order to measure the velocity of the rough surface. The output signal of the detector is a narrow band signal whose center frequency is proportional to the velocity of the surface.
The relation between the geometrical parameters of the optics configulation and the power spectrum of the output signal of the detector is dicussed with the help of Fresnel diffraction theory and spectrum analysis. Especially the relation between the diameter of the illuminated area and the spectral width of the narrow band signal is discussed in detail. A large diameter of the illuminated area is necessary to obtain a narrow band signal. The experimental results demonstrating the soundness of the theory are presented.
