The long wavelength of a CO 2 laser produces significant speckle pattern effects with practical sized beams and detectors where a diffuser is used to scatter the light on to the detector. The authors found the percentage standard deviation of the signal from shot to shot to be described typically by 36/N where N is the Fresnel number defined by the beam and detector sizes. The polar diagram for normal incidence of a single rough surface such as sand blasted gold shows a strong central peak whilst in-depth diffusers such as stacked salt granules or flowers of sulphur are much more nearly Lambertian-salt being virtually perfect. Various absorbing paints and graphite are also assessed.
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Edwards et al. (1981) studied this question.
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