Speckle imaging for surface measurement with low-cost laser diodes

Speckle patterns can be generated by partially coherent illumination of surfaces. In laser optics, such speckles can reduce the image quality dramatically and thus they are not welcome here. On the other hand, it is possible to use speckle patterns for characterization rough surfaces. Very simple laser diodes (1 … 10 mW) are qualified in a set of miniaturized demonstrators. The surface roughness characterization is basing on speckle contrast, speckle modulation, a mean speckle size and the fractal dimension of the speckle pattern. The technique is applied for characterization of human skin. For example melanoma speckle imaging and diagnostics works well and by using high frame rates of up to 300 Hz, the pulse caused pressure variation in blood vessels is measured to visualize the microcirculation in skin. This is done for different skin depths by using different wavelengths (400 … 635 nm).