Digital Speckled-Speckle Interferometry And Its Application To Surface Roughness Measurement

This paper experimentally investigates the spatial correlation properties of the doubly-scattered speckled speckle intensity patterns produced from a cascade of two transparent diffusers. The experiments are conducted by using the digital speckle intensity interferometer under illumination of the speckle pattern. The experimental results show that the fringe visibility depends not only on the rms surface roughness of the diffuser used for producing the speckle illumination but also on the distance between the two diffusers. As a result, we propose the new surface roughness measuring method which has the advantages that the measurable range of the surface roughness and the sensitivity of the measurement are controllable by changing the distance between the two diffusers.