ABSTRACT
Light sources are used for lighting, spectroscopy, and other technical applications. Light comes from many sources, although the most common sources are thermal. Other light sources include gas discharge lamps such as neon and mercury-vapor lamps, which emit light at discrete wavelengths characteristic of the atoms in the lamps, light-emitting diodes, and lasers that emit light at specific wavelengths. A thermal source produces electromagnetic radiation due to the thermal motion of charged particles in the source. Gas-discharge lamps generate light by an electrical discharge through an ionized gas. These lamps use noble gases such as argon, krypton, neon, and xenon. A light-emitting diode is a semiconductor p-n junction diode that emits light due to electroluminescence. Quantum confinement of electrons and holes also reduces the density of states, so less carrier injection is required to achieve lasing. The gain medium in a fiber laser is an optical fiber doped with rare-earth elements such as erbium, ytterbium, and neodymium.
