A method for scanning a surface, consisting of focusing an array of optical beams using optics having an axis, so as to illuminate a region of the surface intercepted by the axis, such that each optical beam illuminates a portion of a respective sub-region within the region. The method further includes moving at least one of the array and the surface so as to cause a translation of the surface relative to the axis in a first direction. During the translation in the first direction, each of the optical beams is scanned over the respective sub-region in a second direction, which is different from the first direction.