Optical microscope angular illumination analysis

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 irradiance achieved by Köhler illumination. A correlation between the angular illumination asymmetry and the contrast in the image of a line grating target was demonstrated as the target is scanned through focus. 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. This ANILAS map is expected to be a useful method for assessing the illumination condition of optical systems.