Apparatus for optical assessment of a sample includes a radiation source, adapted to generate a beam of coherent radiation, and traveling lens optics, adapted to focus the beam so as to generate first and second spots on a surface of the sample and to scan the spots together over the surface. Collection optics are positioned to collect the radiation scattered from the first and second spots and to focus the collected radiation so as to generate a pattern of interference fringes. A detector detects a change in the pattern of the interference fringes as the spots are scanned over the surface.
A method for imaging a surface includes generating a traveling lens in an acousto-optic material and incorporating a traveling mask into a portion of the traveling lens so as to produce a composite traveling lens. The method further includes irradiating the composite traveling lens so as to produce a composite focused beam having a spatial variation across the composite focused beam. The composite focused beam is directed onto a region of the surface so as to generate radiation characteristic of the region from the region. The radiation is imaged onto a detector so as to generate a signal characteristic of the region, responsively to the spatial variation.
