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.
English: This image is a reproduction of an origin...
Dr. Isaac Asimov, head-and-shoulders portrait, fac...
English: This a photograph of an optical table bei...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...