At some point in physics class, we all learn that a light microscope cannot display details smaller than the wavelength of light. Objects closer to each other than about a quarter of a micrometer will therefore blur - no matter how perfect the microscope. In the late 19th century, physicist Ernst Abbe found an explanation for this phenomenon: light is a wave and therefore diffraction does not permit us to focus light onto an area smaller than on third of the wavelength of the light. The basic nature of this problem led to the development of the electron microscope, and, more recently, of the scanning tunneling microscope as well as the atomic force microscope. Today, these microscopes have an extremely high performance and a high enough resolution to display features on a molecular level. Such microscopes tend have one crucial drawback however, insofar as they are usually limited to viewing the surface of a specimen or to viewing a very thin layer. It is due to this fact that light microscopes have remained indispensable in biological and medical research. Not only do they provide three-dimensional images of live cells, they can also map out biochemical processes inside the cell.

For this reason, Stefan Hell's High Resolution Microscopy research group at the Max Planck Institute for Biophysical Chemistry in Gttingen, Germany, pursued the challenging goal of overcoming these century-old limitations - namely in the area of fluorescence. Fluorescence microscopy permits us to target as well as to mark specific sub-cellular components with dyes. After exposing them to light, they fluoresce, thereby disclosing their exact location to us. Recently, the research team demonstrated that it is possible to narrow the focal spot of the fluorescence microscope by applying stimulated emission, a phenomenon well known in laser physics. Immediately after being excited by a (green) light pulse, they are de-excited by a subsequent stimulating (red) light pulse (Stimulated emiss
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Contact: Priv.-Doz. Dr. Stefan Hell
shell@gwdg.de
551-2 01-13 66
Max-Planck-Gesellschaft
10-Apr-2002

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