Whereas the focussing in light optical microscopes is done by glass lenses, electron microscopes make use of rotational symmetric electromagnetic fields to put the electrons back on track. In 1936 Otto Scherzer showed that such lens fields exhibit unavoidable aberrations (spherical and chromatic) as long as the following conditions are fulfilled:
- the lens fields are rotationally symmetric
- the electromagnetic fields are static
- there are no space charges
These aberrations seriously degrade the performance of electron microscopes. They cannot be corrected by combining rotational symmetric lenses.
short vita of Otto Scherzer
He was born in Passau in 1909. He studied physics at the university of Munich from 1927 until 1931. His thesis under the supervision of Arnold Sommerfeld dealt with the quantum theory of bremsstrahlung. From 1932 to 1933 he was working for AEG dealing with electron optics and he habilitated in 1934. In 1935 he became associate professor at the Technical University of Darmstadt and director of the theoretical physics department. In 1936 he proved his famous theorem. In 1954 he was appointed professor in Darmstadt and he was co-founder of the GSI (Gesellschaft für Schwerionenforschung).