Omar Khasawinah 5-26-00
Multi-Channel Holography
Holography is still a rare, yet fascinating field of study. It is still in the early stages of development. For this reason, it is up to the younger generation to study it and help it progress. A hologram is a piece of film that when it is made properly, it appears in 3-D, just as if there was an object inside the film. One will almost want to break the glass and grasp the object. However silly this may sound, it shows the extraordinary appearance that a hologram shows. A hologram can also be made to show an object as if it was in front of the film. This projection of the image would make one want to reach out and feel the object. Weather or not one reaches for the object, they will find that the object is not there. Holography can be described as a "deception of the eyes," in that the eyes would see an object appear with such a real appearance, but the object is not really there. There are many different types of holograms. To name a few, there are transmission holograms, white light reflection holograms, and multi-channel holograms.
Transmission holograms are a unique type of holograms. They are unique in that once they are made, they can only be viewed with a laser light shining on it at the reference beam angle. However, if a hologram of this transmission hologram is made, then the new hologram will be viewable with white light reflecting on it, thus it will be a white light reflection hologram.
White light reflection holograms have a simple setup compared to that of transmission holograms. This type of hologram can be seen with white light shining on the film. White light reflection holography is a relatively simple type of holography among all other types of holography.
Multi-channel holography is perhaps the most fascinating type of holography among all of those mentioned earlier. The setup for a multi-channel hologram is like that of a transmission hologram. This setup is knows as the setup for a master copy, or an H-1. The concept of a multi-channel hologram is to show more than one object on the film using different exposures, or showing different angles of the same object all on one piece of film. In order to make a multi-channel hologram, a few vital steps must be followed. For anyone who has studied holography before, they would know that the ratio of the reference beam to the object beam must be four to one. This means that the reference beam must be four times as powerful than the power at the plate while the reference beam is blocked. The process needed to make the multi-channel hologram is quite simple to explain. For a multi-channel hologram with three different views, the film width must be divided by three. Take for example a 4x5 inch plate. This turns out to be about 1.667 inched for each third of the plate. Now a type of cover must be made to cover each third of the plate. Black paper and electrical tape work well for this purpose. Now cut out six strips of black paper which are approximately 1.667 inches wide and four inched long. Tape these strips of paper over each side of the film, but letting any tape touch the emulsion must be avoided. There would be three different exposures for this hologram. The exposure time for the film should be figured and used during each exposure. For PFG-03 film, the sensitivity is 500 micro joules/cm^2. If the power reading of the laser at the plate with the object in place and the object and reference beams uncovered is 7 micro watts, then the exposure time for the film turns out to be about 56.071 seconds. During the first exposure, the film must be covered with only one third of the plate uncovered. After this exposure is done, the part of the plate that was exposed must now be covered. For the second exposure, the middle third of the plate must be uncovered and the object should be rotated to a different angle, in order to obtain a different view of the object on the final hologram. Just like the first exposure, the exposed part to the film must be covered once again. Now, during the final exposure, the last third of the film must be uncovered and the object should be rotated again. The hologram is now ready to be developed. This type of film must be developed using GP-2 developer. After the proper developing procedure is finished, the hologram is ready to be viewed. This hologram must be viewed with a laser shining on it at the angle of which the reference beam was shining on it. While viewing the hologram, moving from side to side should allow the three different angles at which the hologram was exposed to be seen. This is one of the most fascinating types of holography which is in use today.
This is an overhead view of the setup for a multi-channel hologram.(above)
This is another view of the setup for a multi-channel hologram.(above)
This is the object of which the hologram was taken.(above)
This is me standing by the multi-channel hologram.(above)
Here I am after completing the long process of making a multi-channel hologram.(above)
Email: okhasawinah (at) hotmail.com
