A New Microscopic Principle

IT is known that the spherical aberration of electron lenses sets a limit to the resolving power of electron microscopes at about 5 A. Suggestions for the correction of objectives have been made ; but these are difficult in themselves, and the prospects of improvement are further aggravated by the fact that the resolution limit is proportional to the fourth root of the spherical aberration. Tnus an improvement of the resolution by one decimal wotild require a correction of the objective to four decimals, a practically hopeless task. The spherical aberration of electron lenses has long been the bane of electron microscopy. Enter Dennis Gabor in 1948 with a proposal for an 'electron interference microscope', which did not rely on traditional optical principles. Instead, interference between the illuminating and scattered electron wavefronts was used to record a three-dimensional representation of the object under investigation. This principle is now known as holography.