Re: I need input on practical experiements using holography.

Greetings:
The process of interference between electromagnetic waves
ranging from radio waves to light waves is used for a large 
number of applications. Holography is one of the most
interesting uses of interference. Microwave holograms are
being used to study antennas and to search for hidden
weapons on airline travelers and light wave holograms are
used to prevent tampering with passports, drivers
licenses and now there is a new brand of candy with
editable reflection holograms molded into each piece.

Interference occurs when waves of the same frequency cross
each other. They can be moving in the same direction, in
opposite directions or at an angle to each other. When the 
position of the crests and troughs of two waves match each
other they add and we obtain a bright spot and when the
position of a wave crest matches a wave trough the waves
cancel each other and we get a dark spot. A hologram is
composed of a two or three dimensional array of millions of 
these interference points. I have plotted the development of 
simple one dimensional interference patterns between two
waves traveling in opposite directions in the answer to
a question to Mad Science:

 Physics : Re: When waves collide, do both kinds of interference occur? 
   Adrian Popa, Staff Optical/Microwave Physics, Tue Jan 21 11:42:59 1997

The basic optical hologram is formed from
the interference between two light beams obtained from a
common source, usually a laser. One  beam directly from the laser is
called the reference beam and the second beam is reflected from or
transmitted through an object and is called the object beam. The 
interference between these two beams forms the hologram
which is usually captured on photographic film. The
difficulty in making a hologram is to keep the distance
between the object, the film and some of the optics from
moving less than about 1/10 of a light wavelength during the 
several seconds (about 1 to 30 sec.) required to expose the 
film. This stability usually requires expensive optical
tables, lens and mirror mounts and higher power lasers.
A large amount of information on holography with dozens of
links can be found at the HOLOGRAPHY LINKS PAGES:

http://www.enter.net/~holostudio/links.html

There are three techniques that I would recommend you use to make holograms 
of simple objects that are not as clear as those made on expensive 
equipment; however, these techniques do demonstrate the
process and they form three dimensional images. 
The first technique was developed by one of our Mad Scientists and you can 
form simple images from holograms scratched into Plexiglas. This  technique 
has minimal cost for it does not require a laser or film. The experiments 
are found at the following Web page: 

http://www.eskimo.com/~billb/amateur/holo1.html

The second technique requires a laser and film 
to make  WHITE LIGHT HOLOGRAMS.  Small, complex
objects can be  viewed in 3-D using a white light bulb or a
projection lamp to illuminate the film. High resolution film and a laser 
are required to make the hologram. The reference for
this technique is:

"The Amateur Scientist: How to stop 
worrying about vibration and make holograms view able in white 
light", Scientific American Magazine, May 1989, pages
134-137. 

Scientific American Magazine is available in most
of the larger libraries. If you cannot obtain a copy of the 
article send me an e-mail note and I can send you a copy.

I would recommend that you use the glass mounted 649 type film and use a 
simple red diode laser pointer that you can obtain at Radio Shack stores 
for about $30 or you can buy various pieces of equipment, lasers, optics 
etc. for making holograms and also a hologram setup from the Edmund 
Scientific Company, 101 E. Gloucesster Pike, Barrington, NJ 08007-1380 
(telephone: 609-547-8880 or e-mail . They will send you 
a free catalog with lots of neat science stuff for thousands of 
experiments.

Obtaining the film and developing it will be your most difficult task. I 
would not do fast drying of the film with a hair dryer as suggested in the 
article, letting the hologram dry slowly for a day will provide the most 
crisp images, patience pays off. Also: you will never see a hologram while 
the film is wet, you must have patience and wait for the processed film to 
dry from 12 to 24 hours. Also; I have found that making images of clear 
glass ship models or glass animals placed very close to the front or back 
of the film is the best way to start your experiments until you get good 
holograms. The glass objects reflect lots of light reducing the exposure 
time. 

Third Technique
I have made very nice holograms using a laser and only one lens to expand 
the laser beam to illuminate both the film and the object (as shown below) 
eliminating the need for 2 beams.  This type of ZERO ORDER HOLOGRAM 
considers the part of the beam missing the object and lighting the film to 
be the reference beam. The light reflected from and transmited through the 
object to the film is the object beam. By placing the small glass object in 
front of the film, almost touching it, vibration effects are greatly 
reduced and also gives short exposure times, providing the highest 
probability for success. Don't worry about shadows of the object on the 
film until you make your first sucessful hologram. In later experiments you 
can move the object away from the film to remove the shadow or go on to 
more complex setups..



                 10X OR 20X MICROSCOPE                      
                  OBJECTIVE LENS
                                                   FILM PLATE
                        /\                   /          /
--> -------------------I  I                 /  I       /
                      I    I\             / ___I___   /     
PARALLEL LIGHT        I    I  \          /  \GLASS / /
RAYS COMING FROM      I    I    \      /     \SHIP/ /
LASER                 I    I      \  /             /
----------------------I----I-------FP-------------/--- AXIS
                      I    I      /  \           /
                      I    I    /      \        /
                      I    I  /          \     /         
                      I    I/             \   /
--> -------------------I  I                \ /   
                        \/  SHORT           /      
                         <--FOCAL-->       /    ON PLAY BACK              
                            LENGTH              VIEW HOLOGRAM
                                                 FROM HERE
SIMPLE HOLOGRAM SETUP (DISTANCE NOT TO SCALE)

Best regards - your Mad Scientist - Adrian Popa