ABSTRACT
The electromagnetic spectrum spans wavelengths of many orders of magnitude from long radio waves down to those of atomic dimensions. Electromagnetic radiation can be considered to have the properties of a stream of particles, photons, waves. The former is the basis of geometrical optics theory which is the approach adopted when discussing, for example lens aberrations, whereas the latter tends to physical optics which is used for discussing, polarising microscopy. Specimens are usually prepared by a mechanical lapping sequence followed, in certain special circumstances, by final chemical, electrochemical polishing to remove the ‘flowed’ surface layer. In the electronics industry, the development requirements for thin films have been stimulated by the use of optical systems such as transparent dielectric coatings on optical filters. Photoluminescence relates closely to Raman microscopy and is usually considered in terms of the initial excitation of an electron from the valence band to the conduction band by the absorption of a photon of a particular wavelength.
