Laser

Lasers

A laser is a concentrated beam of monochromatic light.

It is an acronym for Light Amplification by Stimulated Emission of Radiation.

If the wavelength of light is longer than the visible range, the laser is called a maser (m for microwave).

A distinguishing feature of laser light is that its photons are all in phase. They are not just all the same color, but the peaks and valleys of their wavelength line up. This is said to be "coherent".

Early lasers surrounded a lasing medium by a very bright source of light. Optically pure rods from a single crystal of the gemstone ruby were an early lasing medium. Tubes of charged gas were another early lasing medium. These kinds of lasers have reflective surfaces at each end. Laser light oriented perpendicular to the reflective surfaces bounces back and forth, between the reflective surfaces, stimulating the emission of additional light, oriented in that direction. These lasers subsequently emit a beam of light that can be detected over great distances.

Later lasers were developed that were purely electronic -- that is they produced coherent light when supplied with a flow of electrons.

Since lasers were first invented developers have speculated that they could be made to serve as destructive weapon]]s, like the ray guns of early science fiction. However, As of 2026, no practical laser weapons have been designed.