A new approach for determining the roughness of engineering surfaces that is applicable to industrial in-process measurements is introduced. Laser speckle patterns, arising from light scattered from rough surfaces that are illuminated by polychromatic laser light, are detected in the far-field region. The incoherent superposition of these light intensities and the angular dispersion cause the effect of speckle elongation. This is characterized by increasing speckle widths and leads to a radial structure of the speckle patterns. With increasing surface roughness, the elongation is replaced more and more by the decorrelation of the monochromatic speckle patterns for the different wavelengths. Such effects were detected with the CCD technique and analyzed by local autocorrelation functions of intensity fluctuations that were calculated for different areas of the speckle patterns. The results of surface-roughness determination by means of the speckle elongation effect are presented.

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Inspection of the scattered light by two photodetectors makes it possible to investigate the velocities of droplets as well as their size in disperse systems and has some advantages against related methods. When this method is used, the size of the droplets can be derived from the phase difference of the signals from the first and the second photodetector. Special problems of this method are discussed in the paper. A system with fast signal processing facilities, working mostly digitally, was developed in order to solve these problems. This system derives several digital signals from the signals of high frequencies that are gained from the photodetectors. These digital signals are combined by digital circuits of the ECL-type. The resulting pulse series are fed into several digital counters. The data from the counters and from some other inputs are further processed by a real time computer that was developed for this special task, using an 8088 micro processor. This real time computer is connected to an ordinary personal computer by a parallel interface.

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