Single Beam White Light Reflection Hologram


single beam reflection hologram setup
Figure 19: Single beam reflection hologram setup
   
Figure 19 illustrates the optical arrangement for a single beam reflection hologram. The object scene should be placed directly behind the plate holder on the opposite side from the laser beam and almost touching the plate. The plate should be turned more toward the reference beam so the beam hits the plate at an angle of about 45 degrees. This will allow better illumination of the object scene. Do not be concerned if the object scene is not totally illuminated because of the shadow cast by the plate holder. These single beam holograms do not allow much latitude in illuminating the object scene but better illumination will be available when doing the multibeam holograms. The recording and processing procedure for this type of hologram is the same as for the transmission hologram except that you want to end up with an exposure density of 2. The elimination of vibrations and component movement during the exposure is even more critical during a reflection recording. Again, link the plate holder to the object scene holder with an aluminum bar. During the exposure, the laser beam will pass through the hologram plate, illuminate the object scene, and the scene will reflect its light back to the plate. At the same time, the beam passing through the plate serves as the reference beam.
   
reflection hologram virtual image
Figure 20: Reflection hologram virtual image
   
This hologram is viewed differently from a transmission hologram. In Figure 20, the observer is now on the side of the reconstructing reference beam, and again the image is seen looking through the hologram. This is called a reflection hologram because the reconstructing light is reflected from the hologram to the viewer. This type of hologram is best viewed hand-held using a white light source as the reconstructing beam (such as sunlight or a flashlight). A transmission hologram cannot be viewed with white light, only laser light. When viewing with white light, make sure the reconstruction angle is the same as the angle of the original reference beam (just move and/or tilt the hologram until you obtain the brightest image). The original laser light reference beam will work also for reconstruction, but the image will not be as bright as with white light reconstruction.
   
After you produce the reflection hologram on a plate, bleach it and dry it. The hologram will be clear and you will be able to see background objects through the hologram as well as the image. The image will be less bright under these conditions. To increase the brightness of the image, place the plate, emulsion down, on a large area of newspaper and spray the plate with 2 to 3 coats of quick-drying flat black paint. Do not over spray. Use a left to right, right to left sweeping motion when spraying. Now, when you reconstruct the image in white light, it will be much brighter. You can tell the emulsion side from the glass side of the plate (or acetate side if using film) because the emulsion side has a dull finish when inspected under white light whereas the glass or acetate side is shinny.


multibeam transmission hologram

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