Laser

The word laser comes from “light amplification by stimulated emission of radiation.” In stimulated emission, a photon interacts with an excited atom or other quantum system and prompts it to release another photon of the same energy. The process can amplify light rather than merely produce it by ordinary spontaneous emission.

In a common laser design, an energy source first excites a gain medium. Light then passes repeatedly through that medium inside an optical cavity, where stimulated emission increases the light; some escapes as the output beam. Most lasers emit within a narrow range of wavelengths, and their light is coherent: the waves have a stable relationship to one another. Coherence and low divergence allow a laser beam to remain concentrated over distance or be focused to a small spot. Laser systems differ in their materials, wavelengths and output, so “laser” describes a family of devices rather than a single beam type.

The laser grew out of research on stimulated emission and the maser, a device that amplifies microwaves using related physics. In the 1950s, Charles Townes, Nicolay Basov and Aleksandr Prokhorov helped put stimulated emission to practical use in masers and lasers. Their work formed part of the scientific groundwork for optical lasers.

On May 16, 1960, physicist Theodore Maiman and assistant Irnee D’Haenes demonstrated the first operating laser at Hughes Research Laboratories. It used a ruby crystal and produced pulses rather than a continuous beam. The Smithsonian’s collection includes a ruby crystal from Maiman’s experiments, while noting that the precise crystal that first generated laser light cannot be identified with certainty. This history reflects a sequence of theoretical, microwave and optical advances rather than a single isolated discovery.

The properties of laser light make it useful in many fields. Lasers read and write information on optical discs, scan barcodes, transmit data through optical fibres, assist in some eye surgeries, and help researchers study matter and cool atoms. They are also used in measurement and manufacturing, where a narrow, controllable beam can support precise sensing or material processing.

Laser communication is an active application in spaceflight. NASA describes optical links that use infrared light to send data between spacecraft and Earth, with the potential to carry more data in a link than conventional radio-frequency systems. The approach has trade-offs: clouds and atmospheric turbulence can disrupt a beam at ground stations, so suitable location and system design matter.

A laser’s risk depends on its output and how it is used. Direct exposure to sufficiently powerful beams can injure eyes or skin; even a pointer aimed toward a person or vehicle can cause harm, distraction or temporary flash blindness. The U.S. Food and Drug Administration distinguishes laser hazard classes and says higher-powered Class IIIb and Class IV products should be used only by trained people for legitimate applications. Safety measures and the correct classification are therefore part of laser design and use, not optional extras.