LASER TRIANGULATION - FUNDAMENTAL UNCERTAINTY IN DISTANCE MEASUREMENT

We discuss the uncertainty limit in distance sensing by laser triangul ation. The uncertainty in distance measurement of laser triangulation sensors and other coherent sensors is limited by speckle noise. Speckl e arises because of the coherent illumination in combination with roug h surfaces. A minimum limit on the distance uncertainty is derived thr ough speckle statistics. This uncertainty is a function of wavelength, observation aperture, and speckle contrast in the spot image. Surpris ingly, it is the same distance uncertainty that we obtained from a sin gle-photon experiment and from Heisenberg's uncertainty principle. Exp eriments confirm the theory. An uncertainty principle connecting later al resolution and distance uncertainty is introduced. Design criteria for a sensor with minimum distance uncertainty are determined: small t emporal coherence, small spatial coherence, a large observation apertu re.