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Laser
A laser is an optical device that produces radiation. The term "laser" is a composition of Light Amplification by Stimulated Emission of Radiation. A typical laser emits light in a narrow, low-divergence beam with a well-defined wavelength. This is in contrast to a the incandescent light bulb, which emits into a large solid angle and over a wide spectrum of wavelength.
A laser consists of a gain medium inside an optical cavity, with a means to supply energy to the gain medium. The gain medium is a material (gas, liquid, solid or free electrons) with appropriate optical properties. In its simplest form, a cavity consists of two mirrors arranged in order that light bounces back and forth, each time passing through the gain medium. Typically, one of the two mirrors, the output coupler, is partially transparent. The output laser beam is emitted through this mirror.
Principal components:

1. Active laser medium
2. Laser pumping energy
3. High reflector
4. Output coupler
5. Laser beam
Light of a specific wavelength that passes through the gain medium is amplified. Therefore the surrounding mirrors ensure that most of the light passes through the gain medium. Part of the light that is between the mirrors goes through the partially transparent mirror and appears as a beam of light. The process of supplying the energy required for the amplification is called pumping and the energy is typically supplied as an electrical current.
Uses by typical output power
Lasers have many uses in today’s world. In May 1960 the first demonstration of a laser was made by Theodore Maiman. Throughout year it has become a multi-billion dollar industry. The most widespread use of lasers is in optical storage making laser operation. It also is use to make devices such as compact disc and DVD players, in which the laser scans the surface of the disc. Other common applications of lasers are bar code readers...