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Simple Holography
The Easiest Way to Make Holograms
By T. H. Jeong,
Raymond Ro, Riley Aumiller (Lake Forest College)
and Misashi Iwasaki
(Kyoto Institute of Technology)
with
contributions from Jeff Blythe (University of Cambridge)
Edited by Alec Jeong
Copyright © 1996-2007
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1. INTRODUCTION
"Everything should be made as simple as possible, but not simpler” -
Albert Einstein
We attempt to follow
this dictum so you can make holograms easily. The procedures
we propose herein are as simple as it is physically possible. In the
process, we make holography not only as simple as possible, but safer,
less expensive, and more accessible to young people.
The essential items
explained in this article can be used to make many kinds
of holograms, including reflection holograms and
transmission holograms. This article focuses on making reflection
holograms.
2. THE LASER
The figure below shows a Class IIIa diode
laser with an output of 3 to 4 mW when operated by 3.0 v dc. If the power is
supplied by batteries, its red light of wavelength 650 nm achieves a coherence
length exceeding 1 m after a warm-up period of a few minutes. The traditional
helium-neon laser, on the other hand, operates on dangerously high voltages,
is prone to breakage, has a shorter shelf life, and a coherence length of
approximately 30 cm.
Unlike many laser diodes and laser pointers,
the laser shown below and in our catalog has a stabilized frequency output (a
must for holography), good coherence length (also a must), and a removable
collimating lens. With the spring-loaded collimating lens mounted on the
laser, the output beam can be adjusted to focus at any arbitrary distance.
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To make holograms,
we'll actually take off the collimating lens . . . shining this pure
beam right on to the holographic plate and object. |
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To make holograms, we'll actually take off the
collimating lens. Without the lens, the direct output from the laser spreads
out with a highly eccentric elliptical profile. Since the beam
encounters no external optical elements, the light has no mottled patterns
caused by interference and diffractions, and appears perfectly clean. In other
words, we'll be shining this pure beam right on to the holographic plate and
object.
The responsible parent or teacher is advised to
remove the lens and the small tension spring before allowing the student to
use the laser. This way, the power density received by human eyes will not
exceed that received when looking at an ordinary grocery store laser scanner.
When the laser is not in use, replace the collimating lens (with or without
the tension spring). This helps ensure that you won't lose the lens and, more
importantly, will help keep dust out of the laser.
If you are using your own "laser pointer" for making holograms, know many
laser pointers and diodes do not have frequency stabilizing circuits (like the
one above), which is required for holography. Moreover, since most laser
pointers do not have a removable collimating lens, you must buy a special
optical lens to spread the beam. With two lenses (four lens surfaces) through
which the laser beam must shine, there may be many objectionable patterns on
the resulting beam due to the four lens surfaces and the dirt on them.
3. STABLE SUPPORT FOR
LASER
An excellent support for such a small laser is
a wooden clothespin, as shown below. For mechanical stability and
maneuverability, the clothespin holding the laser is stuck into a cup of
sand, salt, or sugar (not pepper!). On the other hand, for schools with
available laboratory hardware, the clothespin can be glued to a rod and
mounted on a lab stand with a right-angle clamp.
The wooden clothespin offers another
advantage. It being a thermal insulator, the laser will reach thermal,
electrical, and frequency stability a few minutes after it is turned on,
assuming batteries are used as its power source. An alternative support would
be a rubber-tipped thermometer holder.
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