ABSTRACT
The terms laser and fiber optics are modern and almost synonymous with modern technology. However, the phenomenon that defines their physical origin is known for a long time, since luminescence from inorganic materials was first observed in 1577 by Nicolas Monardes, who noticed a blue tint in water kept in a container made of a special kind of wood1. Three hundred years later, in 1852, fluorescence was introduced by Stokes as an emission of light. At that time the first spectroscopic principles were formulated2, and subsequently used in 1854 as an analytical tool. Four hundred years after the first observation of luminescence, laser light was used to warm up and cut through metals, alloys and organic tissues. Almost 420 years passed before a sample was cooled with laser light and when in 1997 an optical refrigerator was constructed. In this experiment, due to luminescent cooling, the temperature of Y b3+- doped fluoro-zirconate glass decreased by 16K !
