Interactive Tutorials - Spinning Disk Fundamentals

Interactive Tutorials

Basic Microscopy

Conoscopic Images of Periodic Structures

The conoscopic image seen at the objective rear focal plane is either the diffraction pattern of the specimen (line grating or grid), or in the case of this tutorial, the image of the condenser iris aperture diffracted by periodic spacings in the specimen. When the specimen is illuminated with monochromatic light (by using the appropriate radio button), the diffraction patterns are transformed into periodically repeating sharp images of the condenser iris opening. As the wavelength of monochromatic light is increased (towards yellow and red colors), images of the iris opening become spaced further apart, proportionately with the increased wavelength of light. The opposite occurs when wavelengths are decreased into the green and blue regions of the visible light spectrum, where the iris images are brought closer together.

The purpose of this tutorial is to explore the reciprocal relationship between line spacings in a periodic grid (simulating a specimen) and the separation of the conoscopic image at the objective aperture plane. When the line grating has broad periodic spacings, several images of the condenser iris aperture appear in the objective rear focal plane. If white light is used to illuminate the line grating, higher order diffracted images of the aperture appear with a blue fringe closer to the zeroth order (central) image and with a green-yellow-red spectrum appearing further out towards the objective aperture periphery.

Contributing Authors

Rudi Rottenfusser - Zeiss Microscopy Consultant, 46 Landfall, Falmouth, Massachusetts, 02540.

Tadja Dragoo and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.

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