Holography

I’ve had a talk about “Holography” today. It was a project for my optics class. So I thought It would be a good idea to write a little about this matter.

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Holography is a Greek word meaning “whole-drawing”. This method records the light field instead of only recording a reflection of the object. There are different types of holograms like transmission holograms, reflection holograms, rainbow holograms (which we frequently see used for security on credit cards and passports and etc.)

Two photographs of a single hologram taken from different viewpoints:

Holomouse2

The transmission holograms are made by the interference between a reference beam and an object beam diffracted from the object. These two must be split from a coherent source like a laser. The thing recorded on the film used in this way is not a 3d image, it’s an interference pattern. The part of the planes of interference (which are hyperbolic) that is inside the film will be recorded and it’s really amazing that these planes work as microscopic mirrors with a percent of transmission. This quality of these planes is what causes the re-constructing of the object as a hologram.
The hologram in this method is only observable by using a laser of the same frequency.

Reflection holograms are made by placing a film in front of an object and illuminate the object through it with a laser beam. The reflected beam and the initial beam will interfere in the film(as standing waves).
The planes of interference recorded in this method reflect only the wavelength they were made by. How? The planes’ distance is the key. Only that wavelength which correspond to this distance will be reflected. Shorter the distance, shorter the wavelength. So with this feature of these holograms its easy to see that these holograms are easily observable with white light and there’s no need for a laser of the same frequency to re-construct the object.

Rainbow holograms are of a branch of transmission holograms. What is added for the rainbow holograms is a slit in front of the object. This way only a part of the object beam which is diffracted through a horizontal slit will be observable. The whole object is observable through white light diffraction for every wavelength re-constructs a part of the object and we know that different wavelengths diffract from slit at different angles. So when we rotate the film vertically we see the object in different color, but because of the slit we do not have the vertical parallax anymore (this helps reduce the blurriness of the recorded image). But we still have the horizontal parallax and stereopsis which are the key features of giving our hologram depth.

Holography is used for security, data storage, making holographic tweezers, etc. There are a lot of utilizations for holography, every optical instrument has a holographic kind too (for example a holographic mirror)

We see much of holography in Hollywood movies like the “Iron-Man” movies or famous “Avatar” or in the “Avengers”.
Holographic screens are not that far and soon after we got those we’re going to make interactive ones (as we did for ordinary screens that we use nowadays) .

Researchers of this fields are trying to make holographic videos (motion pictures) with higher fps. So we are not that far at all far from seeing more of holography in our everyday life.

 

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