laser

Laser is an acronym for light amplification by stimulated emission of radiation. It describes devices that emit light through stimulated emission, producing a beam that is typically highly coherent, intense, monochromatic, and collimated. In operation, a gain medium is driven into a population inversion, and photons passing through the medium stimulate further emission of photons with the same wavelength, phase, and direction. An optical resonator, often two mirrors, provides feedback to amplify the light and defines the spectral and spatial properties.

Gain media can be gases, liquids, solids, or semiconductors. The device is pumped by an external energy source, such as electrical current or optical photons, to raise particles to higher energy levels. The photons emitted by stimulated emission are amplified as they bounce between cavity mirrors. Different media produce different wavelengths, enabling a wide range of lasers from infrared to ultraviolet.

Laser development began with the concept of stimulated emission identified by Albert Einstein in 1917. The first working laser was demonstrated by Theodore Maiman in 1960 using a ruby crystal. Early lasers used solid-state crystals and gas discharges; later, dye lasers, semiconductor (diode) lasers, and fiber lasers broadened practical wavelengths, efficiency, and integration into devices.

Applications span industry, medicine, science, and communications. Lasers are used for cutting and welding, precision surgery, ophthalmology, data transmission, sensing, and spectroscopy. Performance factors include wavelength, coherence, beam quality, and power. Safety considerations include exposure hazards to eyes and skin; proper classification, engineering controls, and protective equipment are essential in workplaces and laboratories.