What Is the World Made Of?

Are Emission and Absorption the Only Ways Light Interacts With an Atom?

How was the laser invented?

One of the useful applications of quantum mechanics is in each CD or DVD player in your home, or in the laser pointer. It’s the device that uses stimulated emission of light predicted by Einstein so many years ago. In 1953 Charles Townes (1915-) of Columbia University (and later MIT) developed and patented the first application that he called a “maser” for microwave amplification by stimulated emission of radiation. It used a beam of ammonia molecules and later led to the hydrogen maser, now used as an extremely accurate clock. In 1958 Townes and Arthur Schawlow described how molecules could be used to extend the maser concept to optical frequencies. After their paper was published a number of physicists at university and industrial labs rapidly tried to apply these ideas to working devices.

In May 1960, Theodore Maiman (1927-2007) at Hughes Aircraft Company demonstrated an “optical maser” that used a ruby crystal with a flash lamp (similar to the camera flash lamp) to put the chromium atoms in the ruby into their excited states. Maiman was involved in a court fight over the validity of his patent for the laser with Gordon Gould (1920-2005), who worked with Townes at Columbia. In 1973 Gould was awarded the patent rights. Maiman won number of awards, but never the Nobel Prize.

While the laser was first described as a “solution looking for a problem” over the past fifty years lasers have become a multi-million dollar industry. Lasers have been constructed using gases, as in the familiar helium-neon, or HeNe laser; the carbon-dioxide laser used to cut fabrics and metals; the argon-ion laser used in surgery; the ultraviolet excimer laser used for eye surgery; and the free-electron laser used in research. Lasers made of tiny semiconducting crystals are used in CD and DVD players and laser pointers, as well as optical fiber communications equipment that brings video and the internet almost to your front door. Lasers have revolutionized research in physics, chemistry, and biology.


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