Holography The Complete Book of Holograms By Will

Holography The Complete Book of Holograms By Will Locatelli Background Image from Star Wars (1977)

What is holography? • Holography is a process by which a light field is recorded photographically and reproduced • Developed theoretically by Dennis Gabor in 1948 • Not practical before lasers were developed in the 1960 s, because holographic methods require coherent light Dennis Gabor, AIP Emilio Segrè Visual Archives, Physics Today Collection

How is the image recorded? (Basic Explanation) • Coherent light is reflected off the object onto a sheet of film • A second “reference” beam of light is shined directly at the film • The interference of these two beams is recorded on the film Diagram from source 2.

How is the coherent light created? • A single laser beam is split using a two-way mirror in order to ensure that the reflected light and the reference light are coherent, and then diverged with a lens. Diagram from source 5.

How is the image viewed? • When a beam similar to the “reference” beam is shined on the film, it essentially “reverses” the process, producing a copy of the original picture Diagram from source 2.

But how can the entire light field be recorded on a single film? In order to see how it works, we have to look at a few slightly different examples Iron Man, 2008

Photographic Grating example • The interference of the two light waves produces a pattern on the slide All images from source 2.

Photographic Grating example When a wave set that is very similar to Wave Set A is shined on the plate, they deviate based on the interference pattern on the plate All images from source 2.

Notice how the downward deviated waves in the second diagram match Wave Set B in the first diagram. A viewer standing in the lower right corner of the second diagram would see the same image as someone standing in the same place in the first diagram, if the photographic plate weren’t there. This is called a “virtual image”. All images from source 2.

Interference of spherical waves and plane waves Light radiating spherically from a point will similarly interfere with a set of plane waves. However, it will produce a circular pattern rather than a grating. All images from source 2.

Interference of spherical waves and plane waves • If a reconstructing set of waves is shined on the plate, it will similarly produce upward waves, downward waves, and undeviated waves. If you looked at this image, it would appear as though you were looking at the original point source through a window. All images from source 2.

All images from source 2.

• This diagram shows laser light coming through 3 separate point sources. Each point source produces a pattern on the plate. Although only 2 rings are shown around each point on the plate in the diagram, in reality there would be rings radiating from each point, and the rings coming from each point would intersect with the rings from the other points, forming a more complex pattern. If this plate was illuminated with a reconstructing wave set, a viewer would see all three points. Image from source 2.

Now visualize the illuminated object as being covered in tiny point sources. Diagram from source 3. In holography, the laser light reflected off each point on the object behaves in the same way as light from a point source. The light from each point records its own pattern on every point on the hologram. However, from any one angle, the light from one point on the original object only shows up on one point on the hologram. As the viewer moves around, they see different angles, and the object appears 3 -dimensional for the same reason objects in real life appear three dimensional – a slightly different picture is hitting each eye.

Some holograms from Jason Sapan’s Holographic Studios NYC (next slide) Video from Niko on You. Tube

Sample test questions • True or False: A single point on a plate of film with a holograph on it contains information corresponding to a single point on the object recorded on the film. • Multiple choice: If you were to attempt to create a hologram using a standard white light bulb (rather than lasers), what would happen? A. Nothing would happen. B. The image would appear in color. C. As long as you lit it with a standard light bulb, it would show up fine. D. The image would split into several directions, each a different color.

Sources 1. Serway, Raymond A. , and John W. Jewett. Physics for Scientists and Engineers with Modern Physics. Australia: Thomson/Brooks/Cole, 2008. Print. 2. Kock, Winston E. Lasers & Holography: An Introduction to Coherent Optics. Second, Enlarged ed. New York: Dover, 1981. 3. Kasper, Joseph E. and Steven A. Feller. The Complete Book of Holograms: How they work and How to make them. 1987. 4. Robert Workman. “What is a Hologram? ” livescience. com. 2013. http: //www. livescience. com/34652 -hologram. html 5. What is holography? ” holocenter. org http: //holocenter. org/what-is-holography