One of the most interesting and clever
optical inventions is the laser. Its use has opened the
doors to such devices as your CD player and automatic
checkout scanners in stores.
This probably gets you wondering about
this type of optical device. Questions you may have
include:
How does a laser work?
The word "laser" is an acronym for Light
Amplification by Stimulated Emission of Radiation. That
expression means that the light is formed by stimulating
a material's electrons to give out the laser light or
radiation.
The way a laser creates its radiation is
by using a rod of made of a certain material such as
ruby that has its surfaces partially mirrored. The rod
is bombarded with light or sometimes electrons that
cause atoms in the rod to emit light of a specific
color. The mirrors cause the light to be reflected back
and forth. Each time the light passes through the
material, it stimulates the atoms' electrons to give off
more light. Once the amplitude is great enough, an
intense beam of light energy is emitted through one of
the partial mirrors.
The most common laser color seen is red,
which comes from ruby lasers and some diode lasers.
There are some lasers that emit in infrared. Getting a
laser to emit blue light has been very difficult to do.
What is special about laser light?
If you have ever shined a flashlight at
night, you can see that its beam spreads out, thus
limiting its effectiveness. Although the reflector
around the light bulb sends the light in a parallel
beam, the wave nature of light causes it to spread out.
In a light bulb filament, light is sent
from its various parts in short bursts of energy. These
packets of waves randomly come off the filament, such
that the light beam is an incoherent mixture of all
these bursts of energy.
On the other hand, every time a wave of
light bounces back and forth inside the laser, it
stimulates electrons rotating around the atoms to give
off photons or light waves all at the same time. Thus,
instead of being a random collection of bursts of light
energy, laser light consists of waves all being emitted
and amplified at the same time. This is called coherent
light.
One amazing characteristic of laser
light is that it does not spread out. This is because it
is coherent. While a powerful flashlight or a spotlight
may shine effectively several hundred yards or meters,
laser beams have been bounced off the surface of the
Moon and detected back on Earth.
Another result of being coherent and of
traveling in a narrow parallel beam is that laser light
can be focused to a very small point. If you have ever
used a magnifying glass to focus sunlight to a point,
you can see that you are only able to get a point of
light that is 1/8 inch or 0.5 cm in size. A laser beam
can be focused to 0.01 cm or smaller.
Where are lasers used?
There are many interesting uses for
lasers, depending on the special characteristic being
applied.
Since laser light can be focused to a
very small point of light, lasers are used in CD
players, in surgery and in welding.
An audio CD or a CD-ROM has information
coded in tiny pits on it s surface. A laser light is
focused to get information on the sequence of those
pits. Since regular light cannot be focused to a small
enough point, it is not effective for reading CD
information, while laser light is.
When light is focused, the point of
focus can become hot enough to burn the skin or human
tissue, if the intensity of the light is great enough.
This characteristic can be used to perform surgery that
results in less damage than it a knife or scalpel was
used.
Focusing a very high-energy laser beam
on a piece of metal can actually melt the metal.
Equipment employing high-energy lasers is used in
industry to accurately cut and weld sheets of metal.
Everyone has seen laser pointers that will shine a
narrow beam across the room. Other devices that use this
characteristic are laser range-finders, price scanners,
surveying equipment and laser weapons.
A straight beam from a laser can be
bounced off items as far as the Moon to measure their
distance. They are also used in surveying equipment to
establish a straight line.
A parallel beam of red laser light is
used in the scanners seen in most stores. The beam is
scanned across a bar code and reflected to a detector.
Very high-energy beams of laser light
have been used in space to try to destroy enemy
missiles. The fact that the beam does not spread and
lose its energy is important in being able to damage a
target.
The fact that laser light is so coherent
allows holograms to be made and viewed. We have all seen
the artificial holograms that show somewhat
3-dimensional figures from normal light reflected off a
shiny, etched surface. A true hologram is a film
material that is created using laser light. It usually
also requires laser light to create a realistic
3-dimensional figure in space.
You should be careful when dealing with
lasers, because they can injure your eyes. Since a laser
beam focuses to a point that can get very hot, a beam
shined in your eyes may damage your retina.
Even though many lasers are supposed to
be safe, do not let someone aim a laser pointer at your
eyes. There have been cases of people becoming partially
blind from laser pointers.
I even avoid staring at the light from
the scanners used in stores, just to be on the safe
side.
A laser outputs light that is coherent
and in a highly parallel beam. Laser light can travel
great distances without the beam spreading and can be
focused to a very small point. This type of light has
many modern applications. Also, you should use caution
when looking at laser beams. |