Term Papers on Holograms

Term Paper Title	Holograms
# of Words	1012
# of Pages (250 words per page double spaced)	4.05

Holograms

     Toss a pebble in a pond -see the  ripples?  Now drop two
pebbles
close together.  Look at what happens when the  two sets
of waves combine
-you get a new wave!  When a crest and a  trough
meet, they cancel out and
the water goes flat.  When two crests
meet, they produce one, bigger
crest.  When two troughs collide, they make a single,  deeper trough.
Believe it or not, you've
just found a key to understanding how a
hologram works.  But what
do waves in a pond have to do with  those
amazing three-dimensional pictures?  How do waves make a hologram look
like the
real thing?

It all starts with light.  Without it,
you can't see.  And
much like the ripples in a pond,  light travels in
waves.  When
you look at, say, an apple, what you really see are the
waves of
light reflected from it.  Your two eyes each see a slightly

different view of the apple.  These different views  tell you
about the
apple's depth -its form and where it sits in relation
to other objects.
Your brain processes this information so that
you see the apple,  and the
rest of the world, in 3-D.  You can look around objects, too -if the
apple is blocking the view of
an orange behind it, you can just move
your head  to one side.
The apple seems to "move" out of the way so
you  can  see the orange or even the back of the apple.  If that
seems a bit obvious, just  try looking behind something in a
regular
photograph!  You can't, because the photograph can't reproduce
    the infinitely complicated waves of light reflected  by  objects;
    the lens of a camera can only focus those waves into a flat,  2-D
    image.  But a hologram can capture a 3-D image so  lifelike  that
    you can look around the image of the apple to an  orange  in  the
    background -and it's all thanks to  the  special  kind  of  light
    waves produced by a laser.

          "Normal" white light from the  sun  or  a  lightbulb  is  a
    combination of every colour of light in the spectrum -a  mush  of
    different waves that's useless for holograms.  But a laser shines
    light in a thin, intense beam that's just one colour.  That means
    laser light waves are uniform and in step.  When two laser  beams
    intersect,  like two sets of ripples meeting  in  a  pond,   they
    produce a single new wave pattern:  the hologram.  Here's how  it
    happens:  Light coming from a laser  is  split  into  two  beams,
    called the object beam and the reference beam.  Spread by lenses
and bounced
off a mirror,  the object beam hits the apple.  Light
waves reflect from
the apple towards a  photographic  film.   The
reference beam heads straight
to the film without  hitting  the apple.  The two sets of waves meet
and create a new wave  pattern
that hits the film and exposes it.  On the
film all you can see
is a mass of dark and light swirls-it doesn't
look  like an
apple at all!  But shine the laser reference beam through
the film once more and the pattern of swirls bends the light to re-create
the original reflection waves from the apple -exactly.

Not all holograms
work this way -some us...

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