X-Message-Number: 3577
Date: Mon, 2 Jan 1995 13:52:55 -0800
From: John K Clark <>
Subject: SCI.CRYONICS Finding small objects with light

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  Wrote: 
               
             >Let me also remind them until recently scientist
             >thought is was impossible to resolve with light objects smaller
             >than the wave length  of light.
             
 (Perry E. Metzger)  Wrote: 
             
             >To my knowldege, it is still impossible to do so
             >- -- STMs and AFMs  don't use light.
             
More than 100 years ago Ernst Abbe proved that details smaller
than half the wavelength of the light used to illuminate a
specimen could not be resolved, but he made a hidden assumption,
namely that the distance between the specimen and the source of
light was large compared to the wavelength. In 1956 J.A. O'Keefe
proposed a "scanning near field microscope" that would break the
Abbe barrier. O'Keefe said that if light was emitted from a tiny
hole less than a wavelength away from the specimen the
resolution would be limited only by the size of the hole, the
wavelength would be irrelevant. In 1972 Eric Ash proved
experimentally that O'Keefe was correct.
             
It looks like this technique may soon be practical. In 1993 Eric
Betzig of ATT used visible light from a laser 10 nanometers
above a sample to reveal details of the skeletal scaffolding
inside a cell as small as 15 nanometers. Visible light is about 500 nm.
              
                                     John K Clark       

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