Imaging Characteristics of the Partially Coherent Optical System under Linear Approximation

Abstract

Features of image formation in an optical system under partially coherent illumination are investigated for the case where the imaging process due to a nonlinear system can be assumed to be linear. It is shown that such condition is fulfilled in cases that (1) a small object in the bright background is imaged, (2) an object is imaged by an optical system illuminated with the light radiated from annular source with very narrow width and (3) a low amplitude and phase contrast object (Gabor-Zernike object) is imaged, in a microscope under partially coherent illumination. It is further shown through the evaluation of spatial frequency response in the linear system and observation of computer simulated images that a low phase contrast object becomes highly visible in coherent and near coherent illumination in an ordinary microscope in the presence of defocusing.