Ernst Ruska

Ernst Ruska (1906–1988) was born in Heidelberg and studied electrical engineering in Munich and Berlin. His early research concerned high-voltage equipment, vacuum instruments and cathode-ray oscillographs. He approached microscopy through the practical problem of controlling an electron beam well enough to obtain reliable images.

Working under Max Knoll, Ruska investigated the optical behaviour of electron rays. Hans Busch had already developed a theory describing the focusing action of a magnetic coil. Ruska’s contribution included experimental investigation and the improvement of usable lens structures, not the independent invention of every physical principle involved.

His subsequent career moved between industrial development and academic research. This background is important: electron microscopy required calculations, careful experiments and manufacturable equipment. A successful account of the instrument must explain how those activities were connected.

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A magnetic electron lens uses a suitably shaped magnetic field to influence electron trajectories. Its name describes an imaging function analogous to that of an optical lens, rather than a piece of glass through which the electrons travel. Ruska investigated coils and iron-enclosed structures that could provide shorter focal lengths.

In 1931, the work with Knoll demonstrated that an electron image could be magnified through successive imaging stages. This apparatus is recognized as an early electron microscope because it established the feasibility of multistage electron imaging. It was not yet a convenient general research instrument.

The distinction between demonstration and practical use matters. Specimen heating and limited performance remained serious obstacles. Treating the 1931 apparatus as identical to a later commercial microscope would erase much of the engineering work that made the technique useful.

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In 1933 Ruska completed an improved microscope that surpassed the resolving performance of a light microscope. The development of polepiece lenses was an important part of this progression; he and Bodo von Borries also collaborated on a patent for an optimized magnetic-lens structure.

The short wavelength associated with electrons made finer resolution physically possible, but it did not guarantee the performance of an actual instrument. Beam damage, unwanted magnetic fields, vacuum conditions, contamination and specimen preparation all affected what could be observed.

Ruska’s retrospective account emphasizes this tension. Properties of electron beams that enabled improved imaging also produced practical difficulties. The history is consequently not just a sequence of larger magnification figures. It is a history of making fine detail distinguishable while keeping the specimen and the imaging conditions sufficiently stable.

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From 1937, Siemens supported further development by Ruska and von Borries. Turning a laboratory apparatus into a production instrument required more than reproducing the original experiment: the equipment had to accommodate specimen handling, consistent construction and sustained use. The first series-produced Siemens microscope was delivered in 1939.

Ruska’s brother Helmut, a physician, helped develop biological and medical applications. A visiting laboratory allowed researchers to explore what the instrument could reveal. Instrument development and applications therefore advanced through different but interacting kinds of expertise.

The roles should remain distinct. Ernst Ruska concentrated on electron optics and instrument development, while Helmut Ruska and other collaborators investigated biological specimens and methods. Early biological images cannot all be assigned to Ernst simply because his name is prominent in the history of the microscope. Nor should industrial delivery in 1939 be presented as the original invention of electron imaging.

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After the Second World War, Ruska continued work on rebuilding research and production. In 1949 he took up departmental responsibilities at what is now the Fritz Haber Institute. He later left Siemens and directed the associated electron-microscopy institute from 1957 until 1974. His career thus included sustained technical and institutional development after the original breakthroughs.

Ruska received the Nobel Prize in Physics in 1986 for work in electron optics and electron-microscope development. Gerd Binnig and Heinrich Rohrer were recognized in the same year for scanning tunnelling microscopy. They were not co-builders of Ruska’s 1930s instrument.

The shared award connected different approaches to investigating small structures. Keeping those approaches separate also preserves the stages of Ruska’s achievement: establishing an imaging principle, improving a prototype, developing production equipment and supporting its use as a research tool.

References: [2] [3]