An ultra-fast distance sensor based on dynamic speckles generated by acousto-optic deflection

In this paper, we analyse the applicability of dynamic speckles for distance measurement to any rough surface. The technique is based on spatial filtering of a speckle pattern generated when the object surface is scanned by a laser beam deflected from an acousto-optic device. An extremely short response time was achieved because of the high scanning speed provided by the acousto-optic deflector. We have developed a prototype of the distance-measuring system and studied its performance. The measurement setup has a very simple configuration. The distance can be measured within as short a time as 50 ns, but with rather high inaccuracy caused by the stochastic nature of the speckle effect. The data averaging is easily implemented within a single scan and allows us to achieve an accuracy of 110 mu m within the time window of 2.5 mu s. An analysis of the factors affecting the performance of the proposed technique is carried out. It is shown that the response time can be diminished by an order of value using an acousto-optic crystal with higher acoustic speed. The proposed technique may be useful for monitoring the geometrical parameters of fast moving or rotating surfaces in various industrial applications.