|Why do we need lasers? What do we use lasers for?
How do you build lasers? Who invented lasers? How
big and powerful can lasers be? Why/how do lasers
travel over long distances? Are all lasers red?
What does the color of the laser mean?Why are
|Question Date: 1999-01-16|
Why do we need lasers? What do we use lasers
As you certainly know, a laser is a
(usually) very bright and very focused light
source. We need and use lasers because there are
some tasks which require their brightness and
their focused beam. Lasers are brighter and more
focused than other light sources. One place where
lasers are used is in surgery. The brightness
(sometimes called the intensity) of the beam is
needed to burn through tissue. The focused beam
is also required so that small incisions can be
made. Another place where lasers are used are in
compact disk (CD) players. The laser is used to
carefully read the information on the disk. The
tight beam is needed to read the exact spot on the
disk that you want to read. Similarly, lasers are
used at the supermarket to read prices from bar
codes. Lasers are also used in surveying, because
they provide straight lines. Lasers are also used
in manufacturing for cutting and positioning of
One thing which I have almost
forgotten to mention is that lasers will emit only
a single color of light. You may know that white
light is made up of light of many different
colors: red, orange, yellow, green, blue, violet.
A flashlight, for example, gives off many
different colors, and your eye sees this as white
light. Lasers, as I have mentioned, will only
emit light of a single color.
things a little bit, and I should point out there
are exceptions to some of what I've just said.
There are, for example, lasers which do not give
off a tightly focused beam.
It turns out that there is something
similar to a laser, called a maser that was
invented before the laser. A laser provides an
intense beam of light, while a maser provides an
intense beam of microwaves. When you look at the
physics of light and microwaves, it turns out that
microwaves are also a form of light. It is just
that microwaves are not visible to the human eye.
The maser was invented by Charles Townes
and his students at Columbia University in 1954.
Since the maser and the laser are basically the
same thing, Professor Townes is often thought of
as being the "father of the laser."
Townes together with Arthur Schawlow
worked out many of the principles needed to make a
laser. The first laser was made by a young
physicist named Theodore Maiman at Hughes Research
Laboratories in Malibu in 1960. Maiman's laser
involved the use of a rod of synthetic ruby. The
ruby rod was cut so that the laser beam bounced
back and forth inside the rod, gaining brightness
before emerging from one end.
How do you build
lasers? What does the color of the laser mean?
Are all lasers red?
There are many ways to
make lasers. Some use mixtures of gasses like
helium and neon. Others use organic dyes. Still
others use semiconductors, somewhat similar to
(but different in important ways from) those used
You may have been told that
"laser" is an acronym which stands for Light
Amplification by Stimulated Emission of Radiation.
The best way for me to explain this is to give an
analogy. Think of a two story building. You
might be on the ground floor or you might be on
the second floor. In all lasers, there is a
similar situation where something (you can think
of this "something" as being electrons in the
laser) has the possibility of being in one of (at
least) two positions.
Now, it takes energy
for you to climb the stairs to the second floor,
so we can say that the second floor is higher in
energy than the ground floor. You need some
energy to get to the second floor from the ground
floor, and this energy comes from the food that
you eat. In a laser, we usually put in
electricity to move the electrons in the laser to
the "second floor." Now, if you run down the
stairs from the second to the first floor, you may
get warm and start to sweat. The reason for this
is that you are using energy to run down the
stairs. In a laser, instead of sweating, the
electron will release a flash of light as it drops
from the second floor to the first.
here's the real trick behind the laser. Imagine
that a bunch of your friends were on the second
floor with you, and one or two ran down the stairs
to the first floor. You would probably follow
them. In a laser, a similar thing happens where
the flash of light given off by one electron
falling down, causes other electrons to fall from
the second to the first floor, and in the process
they all give off flashes of light. All of
flashes are pointed in the same
direction, and this means that we get a very
bright and focused beam. In addition, all of the
light flashes are the same color, this is how you
get a beam with only one color present.
color of the laser is directly related to the
energy difference between the "first floor" and
the "second floor" in the laser. With low energy
differences, we get red and infrared (wh
> Who invented lasers?
predated by MASERs (Microwave Amplification by
Emission of Radiation), and the
first folks to work on lasers used their work. But
I'll suppose you can look up who they were in the
> Why do we need
lasers? What do we use lasers for?
pack a lot of optical power into a very small
beam. A laser can be used anytime you want to
focus light (or energy) into a small area. You
could use this for eye surgery, CD players (the
grooves are *really* small), or about 5 other
ideas you can come up with. Give it a
You can also send messages by turning
lasers on and off very quickly (like several
billion times per second!)
> How do you
A laser needs something to
amplify light (like a gas tube, or a ruby crystal)
between two mirrors. if the amplifier can make
light faster than it can escape (through the
mirrors) or be absorbed, you'll have a laser.
Crystals are particularly good at amplifying
light, and when they break, they can form perfect
mirrors at the broken facet. So, the lasers I make
are just a (very) fancy crystal that reflects at
The other thing you need is
energy to "pump" the laser. I pump mine with
electric current, but light can do it too. Why
don't you try to find out how a ruby laser is
pumped? (hint: can you get electricity into a
ruby? can you get light into a ruby?)
big and powerful can lasers be?
& powerful indeed. By arranging an array of lasers
in a grid, I can make it as big and as powerful as
I like. But for some purposes(like weapons, or
cutting steel, or nuclear fusion), it's more
important how intense the beam is (i.e. how much
power can you direct at the same spot). To do
this, I might put a lens in front of my giant
laser grid...as long as I don't melt the
> Why/how do lasers travel over long
Like all light, lasers spread
out as they travel. Shine a laser pointer at the
far end of the hall and you'll see what I mean. To
prevent the light from spreading or being blocked,
laser light is usually focused (with a lens) into
an optical fiber, and transported within it. What
do you suppose fibers are made of?
all lasers red?
I'm making infrared
lasers, my friend is making blue lasers, and
green laser in the next room. So I
would say no :)
> What does the color of
the laser mean?
The color determines the
wavelength of the light, with blue having a
shorter wavelength than red light. Shorter
wavelength light can be focused to a sharper spot,
while longer wavelength light is absorbed less by
glass optical fibers. Of course, it's also the
color our eye sees, and for visual displays
(televisions, lasers shows) you want more colors
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