Chevron error correction method and autofocus optical system for laser scanner

摘要

In a light raster scanning system imaging a medium located on a movable stage and using bidirectional scanning, i.e. scanning during stage movement in two opposing directions, the problem of chevron artifacts (angle errors), due to the different stage movement directions, is overcome by a system of reflective optics including two optical elements dynamically movable relative to one another. One of the optical reflective elements is tilted or rotated relative to the other to compensate for the angle error causing the chevron artifacts. The amount of this tilt is dynamically altered depending on the direction of stage travel and also may be dynamically adjusted to maintain linearity of the scan pattern in spite of any other irregularities in stage velocity. Also an autofocus feature is provided, whereby the two reflective elements are moved relative to one another to dynamically alter the focus of the light beam onto the medium and hence overcome any defocus problems due to irregularities in the medium surface.