Any device that emits light through the process of optical amplification based on the stimulated emission of electromagnetic radiation is a laser. The name laser is an acronym for "light amplification by stimulated emission of radiation". The main difference between a laser and other sources of light is that a laser emits light coherently. The ability of a laser to focus to a tight spot is due to the spatial coherence. For this reason, lasers can be used for cutting and lithography. In addition, spatial coherence allows a laser beam to stay narrow over a long distance.
A laser usually consists of a gain medium. This gain medium acts as a mechanism to supply the laser with energy and provide optical feedback. The gain medium also has certain characteristics that allow the amplification of light by stimulated emission. Therefore, whenever a light of any wavelength goes through the gain medium, it is amplified. However, for a gain medium to amplify light, it requires energy supply through a process called pumping. The energy supplied can either be in the form of a light at a different wavelength (from a flash lamp or another laser) or as an electric current. There is a pair of mirrors on either end of the gain medium, which enable most lasers to use feedback. Light is amplified each time it bounces back and forth on the mirrors in the gain medium.
The Theory Behind Lasers.
According to the classical view, the energy of an electron orbiting an atomic nucleus is larger for orbits further from the nucleus of an atom. In the quantum mechanical, electrons take on discrete positions in the orbital due to the effects force. Normally, electron receives incident quantum of energy when it absorbs energy, but transitions only takes place between discrete energy levels. As a result, lines are emitted and absorbed.
History of Lasers.
As early as 1917, Albert Einstein came up with the theoretical foundation for both the laser and maser.