For high precision applications of optical microscopes, it is critical to achieve symmetrical angular illumination intensity at the sample plane, in addition to uniform spatial intensity achieved by Köhler illumination. In this paper, first we demonstrate a correlation between the contrasts in the image of a line grating target as the target is scanned through-the-focus, and the angular illumination asymmetry. Using this correlation we present a novel yet simple method of experimentally evaluating the angular illumination asymmetry (ANILAS) at the sample plane of an optical microscope across the field of view, which is called ANILAS map and is expected to be a useful method of assessing the illumination condition.
Citation: Optics Express
Pub Type: Journals
Kohler illumination, angular illumination analysis, optical microscope