In an optical scanning system for detecting particles and pattern defects on a sample surface, a light beam is focused to an illuminated spot on the surface and the spot is scanned across the surface along a scan line. A detector is positioned adjacent to the surface to collect scattered light from the spot where the detector includes a one- or two-dimensional array of sensors. Light scattered from the illuminated spot at each of a plurality of positions along the scan line is focused onto a corresponding sensor in the array. A plurality of detectors symmetrically placed with respect to the illuminating beam detect laterally and forward scattered light from the spot. The spot is scanned over arrays of scan line segments shorter than the dimensions of the surface. A bright field channel enables the adjustment of the height of the sample surface to correct for errors caused by height variations of the surface. Different defect maps provided by the output of the detectors can be compared to identify and classify the defects. The imaging function of the array of sensors combines the advantages of a scanning system and an imaging system while improving signal/background ratio of the system.