Strictly speaking, the laser should have been called a loser
Laser stands for light amplification by stimulated emission of radiation. But a laser that makes its own light is really an oscillator, not an amplifier, so physicists have joked that swapping amplification for oscillation, and spelling LOSER, would have been more honest. The less embarrassing acronym stuck.
Theodore Maiman got the first one working in 1960, in a Hughes laboratory in California, building on theory by Charles Townes and Arthur Schawlow and an optical amplifier patented by Gordon Gould. It had a microwave predecessor, the maser, and early light versions were called optical masers. Gould coined LASER in a 1959 paper and hoped for a family of names, XASER for X-rays and UVASER for ultraviolet among them. Instead, anything above microwave frequencies, roughly 300 gigahertz, became a laser, and a verb, to lase, grew out of the noun.
The trick is stimulated emission. In a light bulb or a star, excited atoms release photons randomly at many energies. In a laser, a passing photon of just the right energy triggers an excited atom to release an identical twin, and both can then trigger more, a chain reaction. Most atoms drop out of their excited states too quickly for this, so lasers use materials with metastable states that stay excited longer, while an energy source keeps pumping them up.
What sets laser light apart is coherence. Spatial coherence lets a beam be focused to a tiny, intensely bright spot or stay narrow across great distances. Temporal coherence means a very pure single frequency, and the same property can be exploited to produce pulses lasting mere attoseconds.
Those qualities explain the laser's reach, from fibre-optic communication, disc drives, barcode scanners and printers to chip-making lithography, surgery, cutting and welding, range finding and light shows. It is widely rated among the greatest inventions of the twentieth century. Nature makes its own versions too: astronomers observe masers occurring naturally in space.
Source: Laser
