The optics of microscopy

Abstract

The optical microscope is a standard optical instrument that is used as an example to introduce the principles of optics. However, some of the assumptions that are used to describe image formation are highly suspect. Take the paraxial approximation, for example, which assumes angles are small when in practice they can be greater than 70°. Research into new microscope techniques and improvements in understanding quantitatively the image formation process has led to investigations in various areas of optics including diffraction theory, pupil filters, non-paraxial focusing, vectorial effects, finite Fresnel number, partial coherence, three-dimensional image formation, beam propagation, ultra-short pulse propagation and scattering theory. Some of these topics are reviewed, with particular emphasis on their applications in microscopy. Also, in addition to their intrinsic scientific interest, some of these areas have other applications, in optical information storage and lithography for example. This paper is based on a plenary presentation at Photonics06, Manchester UK, on the award of the Institute of Physics Optics and Photonics Division Prize 2006.