Laser is the abbreviation of the term "light amplification by stimulated emission of radiation." It is an apparatus that emits a special form of light. The emission of light by a laser is known as stimulated emission.

The essential parts of a laser are a gain medium and an optical cavity. There should also be an external source of energy to be supplied to the gain medium. Gain medium is a material that has got the characteristics to amplify light. The gain medium in a laser can be a material in any form (solid, liquid, gas or plasma). The commonly used gain materials as gain media in the lasers are glass, crystals and various gases that can amplify light.

Optical cavity in a laser is made by using mirrors arranged in a particular angle so that they can reflect light to and fro. Normally the cavity between the two mirrors used in this arrangement is filled with gain medium material so as to achieve stimulated emission of light.

Stimulation of light or amplification is achieved by a method called pumping. Pumping is in fact the supply of an external source of energy to the gain medium. The source of energy can be electric current or any other external mode of energy source.Laser

Normally the lights that come from laser appear in a narrow low divergent beam. Laser light is converted to a narrow low divergent form with the help of optical lenses or other optical components. Lasers can also create broader light beams. In any form, light produced by a laser is not natural and is an artificial product of human technology.

Unlike natural lights that come in different wave length and colors, laser light come in a single color or wavelength. For this reason scientists call it "monochromatic" which means single color. Another peculiar feature of a laser light is that it is coherent. The light beams of laser will not vary its time and position and therefore will not spread into other directions. The natural light sources produce incoherent light which usually spread in different directions without keeping a single phase.

Laser light waves travel parallel to each other in a single direction. This peculiar nature of laser light makes it possible to be very narrow to be concentrated even on a tiny spot. Scientists use the term "collimated" to refer this characteristic of a laser light beam. The monochromatic, coherent and collimated nature of laser light makes it a tool to be used for cutting and welding requirements. The highly concentrated nature of the laser lights are also used to examine the minute details of an object. Laser technology is most successfully used in surgical instruments and DVD players.

Laser lights in concentrated form can cause biological damage. Based on its capacity to cause biological damage, laser lights are classified into four classes. Class I, Class IA, Class II, Class IIIA, Class III B and Class IV are the different labels given by the scientists to classify laser lights.