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Vibration is in itself NOT a problem in holography. A holographic
camera could be shaking like mad without in any way disturbing the
hologram. You see, vibration is not the problem. To understand the
problem you have to think about how holograms are made. Basically, two
waves of light meet and interfere on a film plane. The interference of
the light waves form a pattern. If one wave moves it smears this
pattern. By smearing the pattern, its like taking your hands and
smearing a fingerprint. It loses its information as a blur. The same
happens with the hologram. The more one wave moves, the more the
overall wave interference pattern is destroyed, until you dim totally
out. But if both light waves vibrate in unison no smearing occurs.
Now, if your table is stiff, there is much less chance of one wave
moving. The stiffness prevents the table from bending. And it is the
bending that allows one of the light paths to change thereby moving that
light wave in the interference pattern. So, stiffness is the real
consideration in building an isolation table. The stiffer the table, the
brighter the hologram.
RESONANCE
Another interesting related topic is resonance. Too many people build
isolation tables based on some drawing they saw in a badly written book.
Usually, they end up making layers of crap to absorb vibration while
totally failing to deal with stiffness! In so doing they create a
whole new problem. Resonance. Do you remember seeing an old film clip
about this bridge in the Seattle Tacoma region called "Galloping
Gertie"? The winds in the canyon hit the bridge at a resonant frequency
and caused it to wave like a flag before collapsing.
Or, when you sing in the shower and hit a note that makes the whole room
seem to amplify that note. That's resonance. It happens when waves
combine VERY constructively, adding as they match in size with the
container they are placed in.
In table construction, too many layers is like putting a spring on a
spring. You can bet it will resonate. And instead of canceling the
harmful vibrations, you are now amplifying them. Not a good idea.
So be very careful not to build a system that only makes your work
harder. Keep it simple. Make it a stiff one!
LIGHT
There seems to be great confusion about the nature of light. Actually,
it is pretty simple. Think of a basic atom. You have a nucleus and
electrons spinning around it. Electrons are the stuff that makes
electricity. They have an electrical charge. Normally, the atom is a
fairly balanced system. But, if you put energy into this system, you
can pump it up. For instance, if you send electricity in, the electrons
of the electricity bump up against the electrons of the atom. As they
collide its like a billiard ball hitting another billiard ball. The
first ball (electron) transfers some of its energy into the second ball
(electron) and sends it off. In the case of an atom, the electron is
sent up temporarily into a higher orbit. Its something like blowing air
into a balloon. The sphere the balloon occupies gets larger. Now, if
you don't tie off the end of the balloon the air you just blew into it
will come back out. The same thing happens in the atom. And as the
electron returns to a lower orbit it releases the energy that originally
sent it flying up into the higher orbit.
A good way to envision the release of energy is to think of yourself in
a pool of water chest high. If you sweep your arm just below the
surface of the water you make little whirlpools. This is the energy
transferring from the movement of your arm into the water. The energy
swirls like a vortex. I like to think of it as a "corkscrew". A wave
of light is a corkscrew or whirlpool of electromagnetic energy released
as an electron returns from an excited orbit. The sweeping motion of
the electron back to its normal or ground state is like the sweeping
motion of your arm in the water. The electrical charge of the electron
is transferred into a whirlpool of electromagnetic energy spinning off
the atom. And it looks like a corkscrew. Think of how a typical
corkscrew that you use to open a wine bottle looks. Now, turn it on its
side and look at it. Its a sine wave. But that's only if you look at
it sideways. Most drawings in books show light waves in this way.
However, light waves are three dimensional. Hence the corkscrew model.
You can think of the electron as being sheathed in an electromagnetic
field. When it is energized by a collision it gains a bit too much of
this electromagnetic jacket. As the electron returns a little bit of it
twists free and tears off, becoming a free electromagnetic field twisted
like a corkscrew. It twists because of the spinning motion of the
electron. This a photon -a single wave of light.
This is the first in a series of 'Holography Helpers' that Jason has been kind enough to furnish for the benefit and help of all aspiring holographers.
Jason Sapan founded the oldest operating commercial holographic laboratory, Holographic Studios on the east coast. He currently teaches holography at his studio in Manhattan, while continuing his commercial and art hologram business. This lab is one of the first integral holography labs and also offers quality holographic portraits. A great wedding present for any couple.
Frequently Asked Questions
Holography Helpers - Table of Contents
Holographic Studios Home Page
Holography Catalog
©Holographic Studios
2003