New Sub-Surface Microscope allows depth viewing without damaging samples

From Omni Continuum, issue unknown

Nearly 20 years ago Czech scientist Mojmir Petran reported a major advance in optical-microscope technology....and then disappeared behind the Iron Curtain. Now news of the remarkable instrument developed by Petran and his colleague Milan Hadravsky has finally reached the West. Last March, the State University of New York at Stony Brook became the first American institution to receive one of the new microscopes.

Ordinary light microscopes give sharp images of the surface of an object only.

The lenses can be adjusted to focus on planes up to 180 microns ( a thousandth of a millimeter) below the surface of a translucent object, but the clear image coming back from the focal plane is swamped by out-of-focus images reflected from the surface and intervening planes. The result is a blur. To get a clear microscopic picture of a level below the surface, scientists have to damage the specimen by exposing the plane they want to look at.

For example, they grind away the outer layers of fossil-tooth enamel to study the inner ones.

The Petran-Hadravsky microscope overcomes the blurring problem. Scientists can just insert the specimen and peer through the surface at the layers below. Living tissue can be observed in action; the microscope has been used to look at people's eyes, fingers, and teeth.

The Czech researchers eliminated the blurring by placing a slowly rotating copper disc, punctured by a special arrangement of holes, between the light source and the microscope lens. Light from all the planes in the specimen is reflected, but only light returning from the plane of focus hits the holes in the disc and gets through to form an image.

In 1967, when Petran published a paper describing the new microscopy technique in the Western journal Science, no one noticed. Shortly thereafter the Soviet Union invaded Czechoslovakia, and Petran's contacts with the West were reduced. He and Hadravsky continued their work quietly at the Charles University in Plzen.

In 1983 Alan Boyde, an English anatomist, met them during a visit to Czechoslovakia and bought one of their microscopes for his London lab. 'The Petran-Hadravsky microscope would not have come to the attention of the world at this time had it not been for Boyde,' explains Lawrence Martin, a physical anthropologist at Stony Brook and a former colleague of Boyde's. 'He worked hard at publicising the fact that it's doing something totally different from other microscopes.' - Leah Wallach

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