What are lasers?
How are lasers classified?

What are lasers?
A LASER (from the acronym of Light Amplification by Stimulated Emission of Radiation) is an optical source that emits photons in a coherent beam. Laser light is typically near-monochromatic, i.e., consisting of a single wavelength or color, and emitted in a narrow beam. Laser action is explained by the theories of quantum mechanics and thermodynamics. Many materials have been found to have the required characteristics to form the laser gain medium needed to power a laser, and these have led to the invention of many types of lasers with different characteristics suitable for different applications. The laser was proposed as a variation of the maser principle in the late 1950s, and the first laser was demonstrated in 1960. Since that time, laser manufacture has become a multi-billion dollar industry, and the laser has found applications in many fields including science, defense/aerospace, medicine, and consumer electronics.

Lasers benefit engineering applications because of their monochromatic, directional, and coherent characteristics. Being able to control a broad range of laser parameters precisely is what allows mechanical engineers to use lasers for manufacturing processes. Some laser manufacturing activities include cutting, welding, heat treating, cladding, vapor deposition, engraving, scribing, trimming, annealing, and shock hardening. Laser manufacturing processes compete technically and economically with manufacturing processes such as mechanical and thermal machining, arc welding, electrochemical and electric discharge machining, abrasive water jet cutting, and plasma spraying [1].


­But lasers play a pivotal role in our everyday lives, too. The fact is, they show up in an amazing range of products and technologies. You'll find them in everything from CD players to dental drills to high-speed metal cutting mac­hines to measuring systems. Tattoo removal, hair replacement, eye surgery -- they all use lasers. But what is a laser? What makes a laser beam different from the beam of a flashlight? Specifically, what makes a laser light different from other kinds of light? How are lasers classified?


http://web.princeton.edu/sites/ehs/laserguide/index.htm#components

http://www.sme.org/cgi-bin/communities.pl?/communities/ilc/what_are_lasers.htm&&&SME