Laser is an acronym standing for Light Amplification by Stimulated Emission of Radiation, describing a device that produces an intense, highly concentrated beam of coherent light - meaning light in which all the waves are of the same wavelength and travel in precisely the same direction and phase. This combination of properties gives laser light its distinctive characteristics of extreme brightness, tight collimation, and the ability to be focused to an extraordinarily fine point, distinguishing it fundamentally from the diffuse, multi-wavelength light produced by conventional light sources.
The principle of laser operation is based on the stimulated emission of photons from an excited medium - which may be a gas, liquid, solid crystal, or semiconductor material depending on the type of laser - when energy is supplied to it in a process known as pumping. When the atoms or molecules of the medium are excited to a higher energy state and then stimulated by incoming photons of the correct wavelength, they release additional photons of identical wavelength, phase, and direction in a cascading chain reaction that produces the amplified, coherent light beam characteristic of laser output.
In photography and imaging, lasers have found a wide range of important and specialised applications. Laser light sources are used in film recorders and laser printers to expose photosensitive media with exceptional precision and resolution, producing output of the highest quality. Laser scanners use finely focused laser beams to digitise film originals, artwork, and three dimensional objects with great accuracy. In the printing industry, laser imagesetters use laser exposure to produce the high resolution film separations and printing plates required for commercial reproduction of photographic images.
Lasers are also used in holography - the production of three dimensional photographic images - where the coherent nature of laser light is an essential requirement for creating the interference patterns that encode the three dimensional information of a holographic image. In scientific and technical photography, high powered pulsed lasers serve as extremely brief and intense light sources for capturing ultra high speed phenomena that would be impossible to photograph with conventional illumination.
In more recent developments, laser technology underpins the operation of laser based autofocus systems used in some cameras and smartphones, where a laser rangefinder measures the distance to the subject with great precision and speed to assist focus acquisition. Laser light shows and deliberately creative uses of laser beams as photographic subjects have also become established areas of creative and commercial photography in their own right.