Lasers are an important family of light sources, best known for emitting a highly directional beam of a single color. Since the first laser was demonstrated in 1960, many different types have been developed, ranging from tiny semiconductor chips to machine tools the size of a car. Lasers emit light in the visible, infrared, and ultraviolet parts of the spectrum, with the wavelength depending on the material emitting the light. Lasers are important in scientific research and measurement, and have played important roles in over a dozen Nobel Prizes. Important laser applications include long-distance communication through optical fibers, eye surgery, optical disks for data storage and entertainment, holography, machining, fabrication of electronic chips, reading bar codes in stores, laser radar for measurement of distances and velocities, and studying nuclear fusion.
The American physicists Charles H. Townes (1915–) and James Gordon (1928–2013) demonstrated the first amplification of stimulated emission in 1954 in a microwave device they called the maser, for Microwave Amplification by the Stimulated Emission of Radiation. They separated excited molecules of ammonia from molecules with lower energy to create a population inversion. When some excited ammonia molecules emitted microwaves at 24 gigahertz, the radio waves stimulated other excited ammonia to emit identical microwave photons. To increase the amplification, they put the ammonia molecules in a cavity resonant at 24 gigahertz, so the microwaves bounced back and forth and were amplified by stimulated emission from more molecules.
In 1957 Townes sought to extend the maser principle to light waves, which have a frequency tens of thousands of times higher than microwaves. This was not a straightforward problem because it required finding suitable light-emitting materials, producing population inversions for light-emitting states, and devising a resonator in which to amplify the light. The following year, Townes and American physicist Arthur Schawlow (1921–1999), proposed producing stimulated emission in a long, thin cylinder with mirrors on both ends, one of which would transmit part of the stimulated emission. Another American physicist, Gordon Gould (1920–2005), whom Townes had asked about suitable materials, independently came up with the same design and coined the word laser to describe it.
The first to make a laser was the American physicist Theodore Maiman (1927–2007) at Hughes Research Laboratories in California, who used a photographic flashlamp to excite chromium atoms in a ruby rod to emit pulses of red light lasting about a millisecond. Announced July 7, 1960, at a press conference, the world’s first laser was small enough to hold in the palm of your hand, although it required a larger pulsed driver to power the flashlamp.
Hecht, J. (2015). Lasers. In J. Trefil (Ed.), Discoveries in Modern Science: Exploration, Invention, Technology (Vol. 2, pp. 587-592). Farmington Hills, MI: Macmillan Reference USA.
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