ABSTRACT
The word laser is an acronym for ‘‘light amplification by the stimulated emission of radiation,’’ a phrase that
covers most, though not all, of the key physical processes inside a laser. Unfortunately, that concise definition
may not be very enlightening to the nonspecialist who wants to use a laser and cares less about its internal
physics than its external characteristics. From a practical standpoint, a laser can be considered as a source of a
narrow beam of monochromatic, coherent light in the visible, infrared, or ultraviolet parts of the spectrum.
The power in a continuous beam can range from a fraction of a milliwatt to around 25 kilowatts (kW) in
commercial lasers, and up to more than a megawatt in special military lasers. Pulsed lasers can deliver much
higher peak powers during a pulse, although the power averaged over intervals while the laser is off and on is
comparable to that of continuous lasers.
