<title>Surface profile acquisition using dynamic speckles</title>

Abstract

In this work we present the novel technique for z-distance measurement to an optically rough surface using dynamic speckles. The technique is based on the continuous frequency measurements ofthe power modulation ofthe spatially filtered scattered light. The dynamic speckle pattern is created when the laser beam scans the surface under study. The complete optical-electronic system was designed and fabricated for fast measurement of the speckles velocity, its recalculation into the distance, and further data acquisition into computer. The measured surface profile is displayed in a PC monitor in real time. Main advantage of the proposed technique is high scanning speed providing an extremely short response time below 1 js. Important parameters of the system such as accuracy, range of measurements, and spatial resolution are analyzed. Limits of the spatial filtering technique used for continuous tracking ofthe speckle-pattern velocity are shown. Possible ways of further improvement of the measurements accuracy are demonstrated. Due to its extremely fast operation the proposed technique could fmd applications in such areas as online quality control of materials (paper thickness, rolled metal roughness, etc.) moving on production lines with high velocities (up to 20 mIs) or online control of the 3D-shape of complex objects (e.g., electronic circuits) during their assembling.