Laser

The invention: Taking its name from the acronym for light amplification
by the stimulated emission of radiation, a laser is a
beam of electromagnetic radiation that is monochromatic, highly
directional, and coherent. Lasers have found multiple applications
in electronics, medicine, and other fields.
The people behind the invention:
Theodore Harold Maiman (1927- ), an American physicist
Charles Hard Townes (1915- ), an American physicist who
was a cowinner of the 1964 Nobel Prize in Physics
Arthur L. Schawlow (1921-1999), an American physicist,
cowinner of the 1981 Nobel Prize in Physics
Mary Spaeth (1938- ), the American inventor of the tunable
laser
Coherent Light
Laser beams differ from other forms of electromagnetic radiation
in being consisting of a single wavelength, being highly directional,
and having waves whose crests and troughs are aligned. A laser
beam launched from Earth has produced a spot a few kilometers
wide on the Moon, nearly 400,000 kilometers away. Ordinary light
would have spread much more and produced a spot several times
wider than the Moon. Laser light can also be concentrated so as to
yield an enormous intensity of energy, more than that of the surface
of the Sun, an impossibility with ordinary light.
In order to appreciate the difference between laser light and ordinary
light, one must examine how light of any kind is produced. An
ordinary light bulb contains atoms of gas. For the bulb to light up,
these atoms must be excited to a state of energy higher then their
normal, or ground, state. This is accomplished by sending a current
of electricity through the bulb; the current jolts the atoms into the
higher-energy state. This excited state is unstable, however, and the
atoms will spontaneously return to their ground state by ridding
themselves of excess energy.As these atoms emit energy, light is produced. The light emitted
by a lamp full of atoms is disorganized and emitted in all directions
randomly. This type of light, common to all ordinary sources, from
fluorescent lamps to the Sun, is called “incoherent light.”
Laser light is different. The excited atoms in a laser emit their excess
energy in a unified, controlled manner. The atoms remain in the
excited state until there are a great many excited atoms. Then, they
are stimulated to emit energy, not independently, but in an organized
fashion, with all their light waves traveling in the same direction,
crests and troughs perfectly aligned. This type of light is called
“coherent light.”
Theory to Reality
In 1958, Charles Hard Townes of Columbia University, together
with Arthur L. Schawlow, explored the requirements of the laser in
a theoretical paper. In the Soviet Union, F. A. Butayeva and V. A.
Fabrikant had amplified light in 1957 using mercury; however, their
work was not published for two years and was not published in a
scientific journal. The work of the Soviet scientists, therefore, received virtually no attention in the Western world.
In 1960, Theodore Harold Maiman constructed the first laser in
the United States using a single crystal of synthetic pink ruby,
shaped into a cylindrical rod about 4 centimeters long and 0.5 centimeter
across. The ends, polished flat and made parallel to within
about a millionth of a centimeter, were coated with silver to make
them mirrors.
It is a property of stimulated emission that stimulated light
waves will be aligned exactly (crest to crest, trough to trough, and
with respect to direction) with the radiation that does the stimulating.
From the group of excited atoms, one atom returns to its ground state, emitting light. That light hits one of the other exited atoms and
stimulates it to fall to its ground state and emit light. The two light
waves are exactly in step. The light from these two atoms hits other
excited atoms, which respond in the same way, “amplifying” the total
sum of light.
If the first atom emits light in a direction parallel to the length of
the crystal cylinder, the mirrors at both ends bounce the light waves
back and forth, stimulating more light and steadily building up an
increasing intensity of light. The mirror at one end of the cylinder is
constructed to let through a fraction of the light, enabling the light to
emerge as a straight, intense, narrow beam.
Consequences
When the laser was introduced, it was an immediate sensation. In
the eighteen months following Maiman’s announcement that he had
succeeded in producing a working laser, about four hundred companies
and several government agencies embarked on work involving
lasers. Activity centered on improving lasers, as well as on exploring
their applications. At the same time, there was equal activity in publicizing
the near-miraculous promise of the device, in applications covering
the spectrum from “death” rays to sight-saving operations. A
popular film in the James Bond series, Goldfinger (1964), showed the
hero under threat of being sliced in half by a laser beam—an impossibility
at the time the film was made because of the low power-output
of the early lasers.
In the first decade after Maiman’s laser, there was some disappointment.
Successful use of lasers was limited to certain areas of
medicine, such as repairing detached retinas, and to scientific applications,
particularly in connection with standards: The speed of
light was measured with great accuracy, as was the distance to the
Moon. By 1990, partly because of advances in other fields, essentially
all the laser’s promise had been fulfilled, including the death
ray and James Bond’s slicer. Yet the laser continued to find its place
in technologies not envisioned at the time of the first laser. For example,
lasers are now used in computer printers, in compact disc
players, and even in arterial surgery.