Holography – Physics behind holograms. Leow S.T. Aloysius 3O3 (15). Introduction. Ever saw a Star Wars movie and wondered what is that green 3-D image of Yoda? This image is actually a hologram. Background information. Holography was invented in 1947 by Hungarian physicist Dennis Gabor
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Holography – Physics behind holograms
Leow S.T. Aloysius 3O3 (15)
Ever saw a Star Wars movie and wondered what is that green 3-D image of Yoda?
This image is actually a hologram.
Holography was invented in 1947 by Hungarian physicist Dennis Gabor
Did not really advance until the invention of LASER in 1960
He received the Nobel Prize in physics in 1971
It is the process by which three-dimensional pictures can be stored and reproduced by laser light.
A hologram is therefore a record of an image as seen from many viewpoints.
What happens when a photo is taken:1) The shutter opens.
2) Light passes through a lens and hits the photographic emulsion on a piece of film.
3) Silver halide reacts with the light and records its amplitude as it reflects off of the scene
4) The shutter closes
It is a point-to-point recording of the intensity of light rays that make up an image
Each point on the photograph records just the intensity of the light wave that illuminates that particular point.
When we develop the film and make a print of the picture, our brain interprets the light that reflects from the picture as a representation of the original image.
The wavelength affects the wave’s frequency.
This determines its color and is measured in cycles per second, or Hertz (Hz)
Contains different wavelengths traveling in different directions and different phase
Monochromatic ( has one wavelength and one color)
Waves are in phase
White light can be used to make or view photographs but a hologram requires the organized light of a LASER
Holograms record differences in both amplitude and the phase
The light has to start out with one wavelength and one phase in order for the film to record these difference.
1) Light from the LASER is split to form object beam and reference beam.
2) Light from the object beam reflects off the object.
3) The light from the object and the reference beam form an interference pattern on the film.
Shine the light of a LASER on the hologram, in the same orientation as the reference beam
Because both the phase and intensity are reproduced, the image appears three-dimensional
The eye is focused behind the film to see the image suspended in space.
Things you need:
1) A LASER: Helium-Neon (HeNe) lasers are common in holography
2) Diverging Lenses
3) A beam splitter: Uses mirrors and prisms to spread a beam into two
4) Mirrors: To direct the beams of light to the correct location
5) Holographic film: To record light at high resolution
1) The laser points at the beam splitter, dividing the beam into two.
2) Mirrors are used to direct the beams to intended targets (eg. Make sure the object beam hits the object).
3) The two beams pass through diverging lenses and becomes a wide swath of light.
4) The object beam reflects off the object, onto the holographic film.
5) The reference beam hits the holographic film without reflecting off anything but the mirror.
A humorous video on the applications of holograms.
And many more…
The presence of holograms indicates the authenticity of these items
Security holograms are also being used in anti-counterfeiting, identification documents, including credit and phone cards, drivers licenses etc
Various Hollywood movies, specially the science fiction films, have used holographic special effects. (eg. Star Wars, Star Trek)
Holograms are also used as promotional tools on records and CD covers.
Holographic technique is also used in various medical applications. (eg. CAT scans, X-ray, MRI, Ultrasound)