Laser Technology and the Physics of Lasers

A laser is a device that produces an intense, narrow beam of light through a process called stimulated emission. The word laser is an acronym for “light amplification by stimulated emission of radiation.” Unlike ordinary light sources, which emit a jumble of wavelengths travelling in all directions, a laser produces light that is highly coherent, meaning its waves are aligned in phase, and usually of a single colour or narrow band of wavelengths.

Laser action depends on quantum processes in which atoms or molecules absorb energy and are raised to an excited state. When an excited atom is struck by a passing photon of the right energy, it releases a second photon identical in wavelength, phase, and direction. To sustain this effect, the active medium is placed in a laser cavity formed by mirrors that reflect light back and forth, building up the beam through repeated amplification. Energy must be continually supplied, a process called pumping, to keep more atoms excited than relaxed, a condition known as population inversion.

Lasers are built around many different active media, giving rise to gas lasers, solid-state lasers, dye lasers that use organic dyes in solution, excimer lasers that emit ultraviolet light, and free-electron lasers. They can operate continuously or in short, intense pulses. Their precise, concentrated beams have made them central to optics and a wide range of applications, from cutting and measurement to medicine, communications, and scientific research.

Frequently asked questions

What makes laser light different from ordinary light?

Laser light is coherent and usually a single wavelength, with its waves aligned in phase and travelling in nearly the same direction, unlike scattered ordinary light.

What is stimulated emission?

It is the process in which an excited atom, struck by a photon, releases a second identical photon, amplifying the light.

What does the laser cavity do?

The cavity uses mirrors to reflect light back through the active medium repeatedly, building up the beam through continued amplification.