We demonstrate here a method of measuring the position or speed of an object using photoacoustic beam deflection. Two laser beams are utilized: a pulsed one focused normally on the object and a continuous one parallel to the surface of the object. An acoustic wave generated by the pulsed laser is launched from the surface of the object and propagates through the air to the other beam where it deflects the beam. This deflection is measured by a position sensitive detector. The timehyphen;ofhyphen;flight of the acoustic wave is determined from the zero crossing of the beam deflection signal. Multiplying this by the speed of sound gives the distance of the object from the probe beam.
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