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Defocusing microscopy
Author(s) -
Agero U.,
Mesquita L.G.,
Neves B.R.A.,
Gazzinelli R.T.,
Mesquita O.N.
Publication year - 2004
Publication title -
microscopy research and technique
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.536
H-Index - 118
eISSN - 1097-0029
pISSN - 1059-910X
DOI - 10.1002/jemt.20117
Subject(s) - microscopy , optics , curvature , digital holographic microscopy , optical microscope , phase (matter) , phase contrast imaging , microscope , refractive index , phase contrast microscopy , optical path , physics , bright field microscopy , intravital microscopy , differential interference contrast microscopy , materials science , mathematics , biology , geometry , scanning electron microscope , microbiology and biotechnology , quantum mechanics , in vivo
Abstract Transparent objects (phase objects) are not visible in a standard brightfield optical microscope. In order to see such objects the most used technique is phase‐contrast microscopy. In phase‐contrast microscopy the contrast observed is proportional to the optical path difference introduced by the object. If the index of refraction is uniform, phase‐contrast microscopy then yields a measure of the thickness profile of phase objects. We show that by slightly defocusing an optical microscope operating in brightfield, phase objects become visible. We modeled such an effect and show that the image contrast of a phase object is proportional to the amount of defocusing and proportional to the two‐dimensional Laplacian of the optical path difference introduced by the object. For uniform index of refraction, defocusing microscopy then yields a measure of the curvature profile of phase objects. We extended our previous model for thin objects to thick objects. To check our theoretical model, we use as phase objects polystyrene spherical caps and compare their curvature radii obtained by defocusing microscopy (DM) to those obtained with atomic force microscopy (AFM). We also show that for thick curved phase objects one can reconstruct their thickness profiles from DM images. We illustrate the utility of defocusing microscopy in biological systems to study cell motility. In particular, we visualize and quantitatively measure real‐time cytoskeleton curvature fluctuations of macrophages (a cell of the innate immune system). The study of such fluctuations might be important for a better understanding of the engulfment process of pathogens during phagocytosis. Microsc. Res. Tech. 65:159–165, 2004. © 2004 Wiley‐Liss, Inc.