When organic or inorganic specimens absorb and subsequently reradiate light, the process is typically a result of fluorescence or phosphorescence. Fluorescence emission is nearly simultaneous with the absorption of the excitation light as the time delay between photon absorption and emission is typically less than a microsecond. When the emission persists long after the excitation light is exti...

The human eye requires contrast to perceive details of objects. Several ingenious methods of improving the contrast of microscopy images have been designed, and each of them opened new applications of optical microscopy in biology. The simplest and very effective contrasting method is ‘‘dark field.’’ It exploits the scattering of light on small particles that differ from their environment in re...