The word hologram comes from Greek, with holos meaning whole and graphe meaning writing.
see also DNA - Helix to Hologram
A hologram is an advanced form of photography that allows an image to be recorded in three dimensions, in fact a recording of an interference pattern made by the interaction of two beams of light.
If
two stones are dropped into water, waves radiate from
the points of impact. Where the two sets of waves meet,
the waves appear to pass through each other; however,
where a crest of one wave coincides with a crest of the
other wave, an extra high crest will form. Similarly,
two troughs coinciding
will form an extra low trough. A crest and a trough meeting
will cancel each other out. Since light travels in waves, two
light beams crossing will have similar crests, troughs and
level patches, forming light and dark fringes. If a suitable
photographic film is inserted where the beams coincide, it
can record this fringe pattern.
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? 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.
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.
White light from the sun or a light bulb is a combination of every color of light in the spectrum, a mix of different waves that's useless for holograms. But a laser shines light in a thin, intense beam that's just one color. 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 in the world work this way, some use plastics instead of photographic film, others are visible in normal light. But all holograms are created with lasers and new waves.
The first step to making your own hologram is setting up an optical table. This is simply a device to neutralize as many vibrations as possible. When making a hologram even the smallest vibrations (100ths of a millimeter) can cause your image to get ruined. An optical table us usually a very sturdy table that is filled with lots and lots of sand so that vibrations can't reach the mirrors, lenses, etc. easily. This also allows you to position things exactly where you want them on a sturdy base.
To test your table, you usually use our good old friend: the Michelson Interferometer . The idea behind this device is that your laser beam is split into two beams, recombined, then projected onto a surface. This produces a interference pattern. If the pattern is stable, your table is good. If the patter in changing you know that something is causing movement, like air currents, vibrations or just something toughing the table.
If you look at these holograms from different angles, you see objects from different perspectives, just like you would if you were looking at a real object. Some holograms even appear to move as you walk past them and look at them from different angles. Others change colors or include views of completely different objects, depending on how you look at them.
If you tear a hologram in half, you can still see the whole
image in each piece. The same is true with smaller and
smaller pieces.
Holograms have other surprising traits as well. If you cut
one in half, each half contains whole views of the entire
holographic image. The same is true if you cut out a small
piece -- even a tiny fragment will still contain the whole
picture. On top of that, if you make a hologram of a
magnifying glass, the holographic version will magnify the
other objects in the hologram, just like a real one.
Once you know the principles behind holograms, understanding
how they can do all this is easy. This article will explain
how a hologram, light and your brain work together make
clear, 3-D images. All of a hologram's properties come
directly from the process used to create it, so we'll start
with an overview of what it takes to make one.
Surprisingly, Our own DNA seems to exhibit all the traits of
a hologram. Is DNA a hologram projector that creates our
reality......perhaps........
to read more about DNA
compared to a Hologram click here.
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