Lasers

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
by a prism inside the laser cavity. An electron laser is a laser which uses free
electrons pumped to lasing capability by magnets. These are powerful
research instruments because they are tunable and a small number could
cover the entire spectrum from infrared to x rays. They should be able to
produce ver high power lasers now too expensive to produce.

As mentioned before, the laser has many applications in the scientific
community and in our daily lives. In medicine they can be used to painlessly
cut and reseal organs or removing tumours, as well as cosmetic surgery.
Holography is a fun part of the laser technology because lasers are what
creates the holographic images. Microscopic objects can be made into 3D
images using x ray lasers. The information applications of the lasers are for
reading and writing data to CD's. They are used to make high capacity audio
and video recording and playback (music CD's and laser disk players). The
militaries of the world use lasers for many things including tracking enemy
movements and as anti-satellite and ballistic missile defence weapons.

Some people might say that the laser is one of the most important
advances in human technology ever, and some might not, but it is definitely
one of the most important advances in the twentieth century.