lasers

Lasers are devices that emit light through optical amplification based on stimulated emission of radiation. The light is typically highly coherent, monochromatic, and directional. A laser contains a gain medium, an energy source or pump to excite it, and an optical resonator formed by mirrors or other feedback elements that forms the laser cavity. When the gain exceeds losses, photons stimulate the emission of additional photons with the same phase, frequency, and direction, producing an intense beam.

The concept traces to Albert Einstein's 1917 theory of stimulated emission. In the 1950s, masers demonstrated amplification of microwaves; the first laser was built by Theodore Maiman in 1960 using a ruby crystal. Early lasers led to rapid diversification into different media and architectures.

Common laser types include gas lasers such as CO2 and He-Ne; solid-state lasers such as ruby and Nd:YAG; dye lasers; semiconductor diode lasers; and fiber lasers. Diode lasers are compact and efficient, while fiber lasers use a doped optical fiber as the gain medium and are widely used in industry.

Applications span industry, medicine, and communications: cutting, welding, and engraving; laser surgery and ophthalmology; barcode scanners and CD/DVD players; telecommunications and data transfer in fiber networks; and scientific research including spectroscopy and laser cooling.

Safety and regulation: lasers can cause eye injury and skin burns. Safety standards classify products into classes and require protective measures such as eyewear, interlocks, and controlled access, with regulations varying by country and application.