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 мл оллллллллллп  ллллллллл плм  плллмм    ммлллп ол олллн         ммлл
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    ппппп                ппллп      ппппп        ппппппппппппп
          ARRoGANT                CoURiERS      WiTH     ESSaYS

Grade Level:       Type of Work           Subject/Topic is on:
 [ ]6-8                 [ ]Class Notes    [Essay on Holograms      ]
 [x]9-10                [ ]Cliff Notes    [                        ]
 [ ]11-12               [ ]Essay/Report   [                        ]
 [ ]College             [ ]Misc           [                        ]

 Dizzed: 11/94  # of Words:1051  School: ?              State: ?
ФФФФФФФФФ>ФФФФФФФФФ>ФФФФФФФФФ>Chop Here>ФФФФФФФФФ>ФФФФФФФФФ>ФФФФФФФФФ>ФФФФФФФФФ

   Toss a pebble in a pondsee 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 depthits 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, tooif 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 backgroundand 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 spectruma 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 appleexactly.

   Not all holograms work this waysome use plastics instead of photographic
film, others are visible in normal light.   But all holograms are created
with lasersand new waves.

All Thought Up and No Place to Go

   Holograms were invented in 1947 by Hungarian scientist Dennis Gabor, but
they were ignored for years.  Why? Like many great ideas, Gabor's theory
about light waves was ahead of its time.  The lasers needed to produce
clean wavesand thus clean 3-D imagesweren't invented until 1960.  Gabor
coined the name for his photographic technique from holos and gramma, Greek
for "the whole message.  " But for more than a decade, Gabor had only half
the words.  Gabor's contribution to science was recognized at last in 1971
with a Nobel Prize.  He's got a chance for a last laugh, too.  A perfect
holographic portrait of the late scientist looking up from his desk with a
smile could go on fooling viewers into saying hello forever.  Actor
Laurence Olivier has also achieved that kind of immortality a hologram of
the 80 year-old can be seen these days on the stage in London,  in a
musical called Time.

New Waves

   When it comes to looking at the future uses of holography, pictures are
anything but the whole picture.   Here are just a couple of the more
unusual possibilities.  Consider this: you're in a windowless room in the
middle of an office tower,  but you're reading by the light of the noonday
sun! How can this be? A new invention that incorporates holograms into
widow glazings makes it possible.  Holograms can bend light to create
complex 3 D images, but they can also simply redirect light rays.   The
window glaze holograms could focus sunlight coming through a window into a
narrow beam, funnel it into an air duct with reflective walls above the
ceiling and send it down the hall to your windowless cubbyhole.  That could
cut lighting costs and conserve energy.  The holograms could even guide
sunlight into the gloomy gaps between city skyscrapers and since they can
bend light of different colors in different directions, they could be used
to filter out the hot infrared light rays that stream through your car
windows to bake you on summer days.

   Or, how about holding an entire library in the palm of your hand?
Holography makes it theoretically possible.  Words or pictures could be
translated into a code of alternating light and dark spots and stored in an
unbelievably tiny space.   That's because light waves are very, very
skinny.  You could lay about 1000 lightwaves side by side across the width
of the period at the end of this sentence.  One calculation holds that by
using holograms, the U.  S.  Library of Congress could be stored in the
space of a sugar cube.  For now, holographic data storage remains little
more than a fascinating idea because the materials needed to do the job
haven't been invented yet. But it's clear that holograms,  which author
Isaac Asimov called "the greatest advance in imaging since the eye" will
continue to make waves in the world of science.
