The word laser was coined as an acronym for Light Amplification by the Stimulated
Emission of Radiation. Ordinary light, from the Sun or a light bulb, is emitted spontaneously,
when atoms or molecules get rid of excess energy by themselves, without any outside
intervention. Simulated emission is different because it occurs when an atom or molecule
holding onto excess energy has been stimulated to emit it as light.
Albert Einstein was the first to suggest the existence of stimulated emission in a paper
published in 1917. However, for many years, physicists thought that atoms and molecules always
were much more likely to emit light spontaneously and that stimulated emission thus always
would be much weaker. It was not until after the Second World War that physicists began trying
to make stimulated emission dominate. They sought ways by which one atom or molecule could
stimulate many others to emit light, amplifying it to much higher powers.
The first to succeed was Charles H. Townes, then at Columbia University in New York.
Instead of working with light, however, he worked with microwaves, which have a much longer
wavelength, and built a device he called a “master,” for Microwave Amplification by the
Stimulated Emission of Radiation. Although he thought of the key idea in 1951, the first master
was not completed until a couple of years later. Before long, many other physicists were building
masters and trying to discover how to produce stimulated emission at even shorter wavelengths.
The key concepts for a laser emerged about 1957. Townes and Arthur Schawlow, then at
Bell Telephone Laboratories, wrote a long paper outlining the conditions needed to amplify
stimulated emission of visible light waves. At about the same time, similar ideas crystallized in
the mind of Gordon Could, then a 37-year-old graduate student at Columbia, who wrote them
down in a series of notebooks. Townes and Schawlow published their ideas in a scientific journal,
Physical Review Letters, but Could filed a patent application. Three decades later, people still
argue about who deserves the credit for the concept of the laser.
【題組】36. The word “coined” could be replaced by______ .