|THE SECRET LIFE OF LASERS
PETER HAYES EXAMINES ONE OF TECHNOLOGY'S MOST UNDER
Lasers are one of
technologies most overlooked and misunderstood arenas.
Without them there could be no fibre optic cables,
laser/LED printers, holography or CD players - to name
but four possible applications.
Infact there are figures in the industry who believe that
lasers will take over from metal-based "buses"
as a way of passing information through a computer.
However such futuristic ideas will have to wait until
The word "laser" comes from the initials of the
actions a laser beam performs: Light Amplification by
Stimulated Emission of Radiation. It was invented, and
first demonstrated, by the American physicist Theodore H.
Mainman in 1960.
At its heart, laser technology uses a particular brand of
"energy packet" called a photon. These can be
produced in various ways, but in essence it uses a flash
unit covered in some form of man made or natural crystal.
The high burst of light transforms the crystals chromium
atoms, momentarily, from it natural "low
energy" state to a "high energy" state.
When returning to their normal low energy state the
crystal releases the all important photons.
Photons are special in that when they collide they
trigger a domino effect passing on a replica of the
previous model to the next photon. These
"dominos" also travel in perfect straight
lines. In industrial use, the red laser beam is built up
of millions of these re-actions being focused and
controlled by means of mirrors.
The power of lasers lies in its concentration of energy.
At its most defined, powerful enough to burn through
plated steel and controllable enough to be used in
However only selected devices need such power and most
computer applications use a highly scaled down version of
the process, sometimes called a semi-conductor laser.
Laser printers use these forms of low-power laser, that
is invisible to the human eye, in its printing process.
However nowadays many printers prefer a Light Emitting
Diode (LED) process that employs highly similar
Low power lasers form a vital part of telecommunications
as they are the main communication medium of fibre-optic
cabling. Needing little in the way of power - and
therefore using semi-conductor lasers - the beam is
controlled to produce short flashes of light - that is
passed to the cable by way of a lens.
In CD applications the lower power laser reads the
digital one's and zero's on the disc that are contained
in tiny holes officially called "pits." This
beam is reflected on to a device called a
"photodiode" that translates the
"disturbed" beam pattern into binary
information. This information can be used as either
computer data or translated into music or film.
Curiously holography predates lasers having been invented
by the Hungarian born Professor Gabor in 1947. He
combined the greek words "holos" and
"grama" to mean the whole message, because it
formed a complete picture.
However it would be 1961 before science harnessed lasers
to create the kind of 3D image we would recognise today.
A normal photography is 2D because all that is captured
on film is light and shade. Holography-based photography
captures depth by measuring (by laser) the distance the
light has travelled and then - through a highly
complicated computer procedure - translates this
information to a set "fixed view" picture with
small variations of the image stored in a way that they
will only be displayed when the image (or human head) is
The use of lasers took a sinister term with the Strategic
Defence Initiative (SDI) or "Star Wars"
programme - which looked for new ways of using lasers to
shoot down enemy missiles from space.
For this the Americans started to develop a new form of
laser using hydrogen and flourine that combines to create
an extremely powerful burst of laser power.
Such a chemical formed laser - using perhaps as much as
25 megawatts of energy - could destroy an object over
2,000 miles away...