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Optical microscopy in the dark-field (OM-DF) configuration yields images that are produced specifically via large-angle scattering of light by specimens because the image generated by light transmitted and light scattered at the small scattering angles by the specimen is formed beyond the angular field of view of the microscope objective. This is a form of spatial filtering of the image (analog Fourier filtering). OM-DF is rather sensitive to particulate contaminants of the specimen or the microscope slide which can significantly contribute to the large-angle scattering. Aside from the dependence on the scattered light for the image formation, the OM-DF has the same optical resolution limitations as the light-field optical microscopy. When used with an imaging device, such as a CCD camera, the image resolution is the smaller of the resolutions of the optical microscope and the camera.
Boustany et al (2001) report on a novel variant of the OM-DF, termed optical scatter imaging (OSI), for examining optically-thin specimens. OSI permits to characterize components of a specimen with sizes smaller than the resolution of the camera that is coupled with the optical microscope. It also enables observing morphological changes in the specimen that are difficult to discern with the conventional optical microscopy.
Briefly, the angular distribution of light scattered by the specimen is sampled sequentially at two angular ranges: 2° to 10° and 2° to 67° yielding two images of the specimen. As the angular distribution of light scattered by the specimen components depends on both their refractive indices and particle sizes, the ratio of the two images is a sensitive indicator of these parameters of the specimen components. Thus, OSI is an imaging form of laser diffractometry. See also a more recent review of this technique by Boustany and Thakor (2003).
| CITATION: Jonasz M. 2006. Optical scatter imaging (OSI) (www.tpdsci.com/Tpc/OSI.php). In: Top. Part. Disp. Sci. (www.tpdsci.com). |
HISTORY: Published: 12-Jan-2006 Modified: 21-Jun-2006 Peer-reviewed: PENDING |
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