Daniel W. Costanza

Development of a precision high-speed flying spot position detector

The theory design and performance of a fast precision flying spot laser scanner position detector are described. Using Fourier analysis a sampling requirement has been derived that assures sufficient information is contained in the samples of the flying spot profile for accurate calculation of its centroid. The derivation shows that for accurate geometric moment determination sampling can be done at a rate lower than that required by the Whittaker-Shannon sampling theorem which applies to complete reconstruction ofthe distribution. A formula for the calculation of moments from the samples is given. A numerical analysis is performed to quantify the accuracy of the calculated first moment for non-ideal sampling conditions. The theory is applied to a laser beam position detector taking into account the irradiance profile the sampling aperture the number of samples required quantization and noise. The predicted performance is compared with experimental results. 1.