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A screen in the center is labeled hologram, reconstruction. Rays labeled reference wave pass through it from left to right. A dinosaur to the right is labeled real image. The dinosaur is facing left. Rays from the screen fall on it. A faded image of a dinosaur facing right is shown to the left of the screen. This is labeled virtual image. Rays from here pass through the screen and reach the eye of the observer.
A transmission hologram is one that produces real and virtual images when a laser of the same type as that which exposed the hologram is passed through it. Diffraction from various parts of the film produces the same interference pattern that was produced by the object that was used to expose it. (credit: modification of work by Mariana Ruiz Villarreal)

The hologram illustrated in [link] is a transmission hologram. Holograms that are viewed with reflected light, such as the white light holograms on credit cards, are reflection holograms and are more common. White light holograms often appear a little blurry with rainbow edges, because the diffraction patterns of various colors of light are at slightly different locations due to their different wavelengths. Further uses of holography    include all types of three-dimensional information storage, such as of statues in museums, engineering studies of structures, and images of human organs.

Invented in the late 1940s by Dennis Gabor (1900–1970), who won the 1971 Nobel Prize in Physics for his work, holography became far more practical with the development of the laser. Since lasers produce coherent single-wavelength light, their interference patterns are more pronounced. The precision is so great that it is even possible to record numerous holograms on a single piece of film by just changing the angle of the film for each successive image. This is how the holograms that move as you walk by them are produced—a kind of lens-less movie.

In a similar way, in the medical field, holograms have allowed complete three-dimensional holographic displays of objects from a stack of images. Storing these images for future use is relatively easy. With the use of an endoscope, high-resolution, three-dimensional holographic images of internal organs and tissues can be made.

Summary

  • Holography is a technique based on wave interference to record and form three-dimensional images.
  • Lasers offer a practical way to produce sharp holographic images because of their monochromatic and coherent light for pronounced interference patterns.

Key equations

Destructive interference for a single slit D sin θ = m λ for m = ± 1 , ± 2 , ± 3 , .. .
Half phase angle β = ϕ 2 = π D sin θ λ
Field amplitude in the diffraction pattern E = N Δ E 0 sin β β
Intensity in the diffraction pattern I = I 0 ( sin β β ) 2
Rayleigh criterion for circular apertures θ = 1.22 λ D
Bragg equation m λ = 2 d sin θ , m = 1 , 2 , 3 .. .

Conceptual questions

How can you tell that a hologram is a true three-dimensional image and that those in three-dimensional movies are not?

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If a hologram is recorded using monochromatic light at one wavelength but its image is viewed at another wavelength, say 10 % shorter, what will you see? What if it is viewed using light of exactly half the original wavelength?

Image will appear at slightly different location and/or size when viewed using 10 % shorter wavelength but at exactly half the wavelength, a higher-order interference reconstructs the original image, different color.

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What image will one see if a hologram is recorded using monochromatic light but its image is viewed in white light? Explain.

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Practice Key Terms 2

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Source:  OpenStax, University physics volume 3. OpenStax CNX. Nov 04, 2016 Download for free at http://cnx.org/content/col12067/1.4
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