The laser is a device that a beam of light
that is both scientifically and practically of great use because it is
coherent light. The beam is produced by a process known as stimulated emission,
and the word “laser” is an acronym for the phrase “light amplification
by stimulated emission of radiation.”
Light is just like radio
waves in the way that it can also carry information. The information is
encoded in the beam as variations in the frequency or shape of the light
wave. The good part is that since light waves have much higher frequencies
they can also hold much more information.
Not only is the particle
the smallest light unit but it is a particle as well as a wave. In beams
of light whether they are ordinary natural or artificial the photon waves
will not be traveling together because they are not being emitted at exactly
the same moment but instead at random short bursts. Even if the light is
of a single frequency that statement would also be true. A laser is useful
because it produces light that is not only of essentially a single frequency
but also coherent, with the light waves all moving along in unison.
Lasers consist of several
components. A few of the many things that the so-called active medium might
consist of are, atoms of a gas, molecules in a liquid, and ions in a crystal.
Another component consists of some method of introducing energy into the
active medium, such as a flash lamp for example. Another component is the
pair of mirrors on either side of the active medium which consists of one
that transmits some of the radiation that hits it. If the active component
in the laser is a gas laser than each atom is characterized by a set of
energy states, or energy levels, of which it may consist. An example of
the energy states could be pictured as a unevenly spaced ladder which the
higher rungs mean higher states of energy and the lower rungs mean lower
states of energy. If left disturbed for a long time the atom will reach
its ground state or lowest state of energy. According to quantum mechanics
there is only one light frequency that the atom will work with. There are
three ways that the atom can deal with the presence of light either it
can absorb the light, or spontaneous emission occurs, or stimulated emission
occurs. This means that if the atom is at its lowest state that it may
absorb the light and jump to its high state and emit extra light while
doing so. The second thing it may do is if it is at its highest state it
can fall spontaneously to its lower state thus emitting light. The third
way is that the atom will jump from its upper state to its lower state
thus emitting extra light. Spontaneous emission is not effected by light
yet it is rather on a time scale characteristic of the states involved.
That is called the spontaneous lifetime. In stimulated emission the frequency
of the light is the same as the frequency of the light that stimulated
center, excimer, free-electron, gas-dynamic, helium-cadmium, hydrogen-fluoride,
deuterium-fluoride, iodine, Raman spin-flip, and rare-gas halide lasers
are just a few of the many types of lasers there are out there in the world.
The helium-neon laser is the most common and by far the cheapest costing
about $170. The diode laser is the smallest being packed in a transistor
like package. The dye laser are very good for their broad, continuously
variable wavelength capabilities.
The theory of stimulated
emission was first proved by Albert Einstein in 1916, then population inverse
was discussed by V. A. Fabrikant in 1940. This led to the building of the
first ammonia maser in 1954 by J. P. Gordon, H. J. Zeiger, and Charles
H. Townes. In July of 1960 Theodore H. Maiman announced the generation
of a pulse of coherent red light by means of a red crystal- the first laser.
In 1987 Gordon Gould won a patent he had been trying to get for three years
to build the first gas-discharged laser which he had conceived in 1957.
In that same patent the helium-neon was included.
Bertolotti, M., Masers and lasers: An
Historical Approach (1983);
Kasuya, T., and Tsukakoshi, M., Handbook
of Laser Science and Technology
(1988); Meyers,Robert, ed., Encyclopedia
of Lasers, 3d ed. (1989); Steen, W. M., ed., Lasers in Manufacturing (1989);
Whimmery, J. R., ed., Lasers: Invention to Application (1987); Young, M.,
Optics and Lasers, 3d rev. ed.