The Laser

Before we can learn about the laser we need to know a little bit about
light (since that is what a laser is made of). Light from our sun, or from an
electric bulb, is called white light. It is really a mixture of all the
different colours of light. The colours range from violet, indigo, and blue, to
green, yellow, orange, and red. These make up the visible part of the
electromagnetic spectrum. Light is made up of particles, called PHOTONS, which
travel in waves. The difference in the colour depends on the wavelength of the
light. Violet light has the shortest wavelength while red has the longest. There
are other parts of the electromagnetic spectrum which includes infra-red, radar,
television radio and micro- waves (past red on the spectrum), and on the other
end of the spectrum are the other invisible radiations, ultra- violet, X rays,
micro waves and gamma rays. The wavelength of the light is important to the
subject of the laser. A laser is made up of COHERENT light, a special kind of
light in which the wavelengths of the light are all the same length, and the
crests of these waves are all lined up, or in PHASE. The word Laser is an
acronym for Light Amplification by Stimulated Emission of Radiation. What does
that mean? Basically a laser is a device which produces and then amplifies light
waves and concentrates them into an intense penetrating beam.

The principles of the laser (and it\'s cousin the maser) were established
long before these devices were successfully developed. In 1916 Albert Einstein
proposed stimulated emission, and other fundamental ideas were discussed by V.A.
Fabrikant in 1940. These ideas, followed by decades of intensive development of
microwave technology set the stage for the first maser (a laser made up of
micro-waves), and this in turn helped to produce more advances in this area of
science. These efforts cumulated in July 1960 when Theodore H. Maiman announced
the generation of a pulse of coherent red light by means of a ruby crystal-- the
first laser.

Laser light is produced by pumping some form of energy, such as light, from
a flash tube (see below) into a LASING material, also known as a medium. Media
can be liquids, solids, gases, or a mixture of gases, such as the common helium-
neon laser (see chart). Each medium produces a laser with a different wavelength
and therefore each medium produces different coloured light. When the energy, in
this case photons (light particles) enter the medium they smash into the atoms
of the medium. The atom then releases another photon of a specific wavelength.
When a loose photon hits an atom that hasn\'t emitted it\'s extra photon, both
photons are released. That is called stimulated emission of radiation. A single
flash from a flash lamp emits billions of pairs of photons into the medium. The
photons are then released as coherent light.

The first laser, a ruby laser, was made up of several main components. It
had a flash tube coiled around a central rod of synthetic pink ruby. In this
case the ruby is the medium. A quartz tube was located just underneath the ruby
rod. A trigger electrode was connected to the quartz tube. All of this was
enclosed in a polished aluminum casing. This was cooled by a forced air supply.

This design was thought to be good enough but later an optical resonator
was added to redirect light in the right direction which increased laser
performance. The optical resonator was a mirror at one end of the laser to
redirect light back into the laser and a partially reflective laser which lets
some coherent light through.

Today there are many types of lasers which include solid state lasers,
which have a solid media. The most common of this is a rod of ruby crystals and
neodymium-doped glasses and crystals. These offer the highest energy output of
all lasers. Another laser type is the gas laser, which can be made of a pure gas
or a mixture of gases or even a vaporized metal in a quartz tube. The helium-
neon laser has hight frequency stability and Carbon Dioxide lasers are the most
efficient and powerful continuous wave lasers. The most compact type of laser is
the Semiconductor laser, made from layers of sem i-conducting materials. Since
these can run by direct application of electrical current these have many uses,
such as CD players and laser printers. Liquid lasers are usually made with a
synthetic dye. Their frequency can be adjusted