Speckle Contrast Measurement with Low Light Levels and Imperfect Laser Illumination

摘要

The contrast of a speckle pattern, denned as the ratio of the standard deviation of intensity to the mean intensity, is an important parameter that can yield useful information in vibration analysis, and surface roughness measurement. It is also of inherent interest in the measurement of scattering by coherent X-rays. Under some circumstances, the light levels at which contrast measurements must be made are low, and the measurement of speckle fluctuations is complicated by the presence of noise associated with discrete detected photoevents. In addition, the measurements are made over a finite integration time and a finite integration area, so it is the contrast of the integrated intensity that is of interest.