A Technical History of the Laser

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From bar code readers to DVD players, lasers are all around us. In fact they have become such an indispensable part of twenty-first century life it’s hard to believe the laser was once described as “a solution in search of a problem.”

The story of the invention of the laser can be divided into three parts: the theoretical work, the practical realization of the first laser, and then the explosion of development that followed.

It was Albert Einstein who proposed, back in 1917, that it might be possible to persuade an atom to emit a photon of light. This would happen, he postulated, if an electron in orbit around a nucleus could be moved from one energy state to another. This process was christened “stimulated emission,” but it remained just an idea until the 1950’s.

That was when Charles Townes and Arthur Schawlow, working at Bell Laboratories, came up with a way to apply Einstein’s idea to the amplification of microwave radiation, then being investigated for radar and communication systems. This device was given the acronym MASER, for “microwave amplification by stimulated emission of radiation.”

Townes and Schawlow speculated that the same principles could be applied to visible light and in 1958 a patent application was filed for an “optical maser.” However, it was left to Theodore Maiman, working at the Hughes Research Laboratories, to turn this idea into reality, creating the world’s first LASER in 1960.

This consisted of a ruby placed inside a coiled fluorescent tube. Lighting the tube sent a stream of photons into the ruby which stimulated the emission of yet more photons. Mirrors placed at each end of the ruby reflected these photons back and forth, resulting in the release of yet more photons and creating a coherent beam. By ensuring that one of the mirrors was partially transparent, some of the light could escape, emerging as a narrow, monochromatic beam.

However, as often happens in the world of research, Townes, Schawlow and Maiman were not the only people working on stimulated emission of radiation. In particular, in 1959 Gordon Gould, then a doctoral student at Columbia University, published a paper entitled “The LASER, Light Amplification by Stimulated Emission of Radiation.” Gould applied for a patent on this device in 1959, some months after the filing by Townes and Schawlow. The resulting legal battle lasted 28 years, ending in 1987 when Gould finally won recognition for his invention.

The ruby laser was not without problems, and within months other researchers were investigating alternative lasing media. At the very end of1960 Ali Javan, working at Bell Labs, used a mixture of helium and neon gases to create the first gas laser. This had the advantage of emitting a continuous rather than a pulsed beam, and as a result it became widely used throughout the 1960’s and 70’s.

1964 saw the invention of the carbon dioxide laser by Kumar Patel, also working at Bell Labs, followed in 1965 by the chemical laser. These produce very high power infrared beams so are primarily of interest for their military applications. At the other end of the spectrum, in the ultraviolet region, is the excimer laser, invented in Moscow in 1970. The excimer is essentially a gas laser, but one that uses chemically inert gases to produce very short wavelength light.

More recently, semiconductor lasers have come to dominate, at least in terms of numbers manufactured. The semiconductor laser is similar to the light emitting diode found in many electronic devices, but to create a laser many such diodes are combined into a “stack” so as to maximize their power. The big advantage of semiconductor technology is that it is low cost, and this resulted in the explosion in laser applications since the mid 1980’s.

Besides bar code scanners and DVD players, lasers are used in fields as diverse as surgery, (including LASIK eye correction,) metal cutting and marking, and research. However, one of the most important application areas may well be communications. Visible light is able to carry a greater density of information than can radio waves, so lasers, combined with fiber-optic cables, are now used to carry much of the world’s telephone traffic.

The laser has been in use for just fifty years yet in that time it has become an indispensable part of human lives. Not bad for a solution in search of a problem!

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