Imagine a situation, of yourself walking on the road while physically being comfortably seated in a room. Well, that seems a little weird!
Putting you in front of one more situation, imagine you see an already dead person sitting forever in front of you. Huh! that sounds petrifying.
Wait, let me explain, all these above-discussed conditions are possible with a very fascinating topic of physics that is holography.
Just to start, we can record our sound in recorders which would be exactly a facsimile of our voice (sound vibrations). And obviously, these recorded sound vibrations can be accessed anytime.
Drawing analogy from sound waves is it possible to record light waves falling on an object at a particular instant and then play these recorded light wave vibrations just like sound vibrations to see the same object even in the absence of the object?
what are holograms?
Holograms are real-time recordings of the interference pattern of the light wave. It is a kind of photographic recording of a light field. They are like 3-D ghost images that are characterized by a special property of appearing to follow as we change our position concerning the recording i.e., they have motion parallax. They give us a stereoscopic view i.e. we see two different images from each eye that create a perception of depth.
The first hologram was developed by Dennis Gaber in the 1940s.
Holograms hold an appreciable potential for changing our future lives. Crude representations of simple objects have been changed to tools used by medical communities, artists, businesses, and even government agencies (security).
Now here I would especially mention an eccentric property of the hologram is motion parallax. This is a very distinctive property that makes holograms look damn concrete even more than 3D images in 3D movies.
Motion parallax is a property whereupon we can see different images depending upon where we stand in front of the hologram. This is something unusual!
Now, let’s progress to see the applied physics behind this high-tech.
Recall, a regular photograph, I think it obviously looks the same whatever be our position concerning the photograph!
So, firstly we’ll go right back to our basics (i.e., photographs) to further understand the holograms.
How, are photographs made?
Firstly, to start with we have an object (or the subject of the photograph) and the white light bounces off or scatters off the object and this scattered or reflected light passes through the lens of our camera and further hits the CCD (Charge-coupled device) or maybe a photographic plate then encoded on the photographic plate and the bounced light intensity is obtained.
Now, there is a property of light called phase which delineates the distance the light travelled while propagating from the source to the subject.
We cannot capture the phase of light in case photographs but in holograms, we can.
In the case of a photograph, we see the photograph due to the white light which is like waves of disparate wavelengths or colours in different directions as the light spreads out. The beam reflecting off the photo freeze-frames the white light crowd. It’s all stagnant. But with holograms, we can move that is it provides a parallax effect. This is due to the difference in setup for the formation of a hologram.
Have a look at this setup-
This is a setup to make one type of hologram (namely transmission hologram)
A ray of light emerges from the laser which is split into two rays by the beam splitter. These two split rays go through lenses and spread out. one beam, the object beam bounces off the object and shines at the holographic film. The other beam called the reference beam bounces off the mirror first and then passes through the lens.
What types of laser allowed it to be used in holography?
Lasers are quite different from normal white light, in lasers all the component rays are in the same phase, possessing the same wavelength i.e., they are coherent. And this plays a key role in making holograms. When two coherent beams meet, they create regularly striped interference patterns.
Here in this case, among the split beams the reference beam is coherent but the object beam is not. When they meet, they create a special type of interference pattern that encodes specific 3D information about the subject in a holographic film. The reference beam is sent back to the hologram, this is how we get the original object beam. That’s the same beam that was created when the laser shined off the object. The reproduced beam of light is a perfect copy of the image such that we can’t tell whether we are looking at light.
Now, this got too serious. Let’s see some cool examples of real holographic technologies.
1)Laser Plasma hologram:
A true 3D display that produces bright dots in the air. So, we can see the 3D images in real 3D space. They use a miraculous technology of plasma emission.
2) Fan-type hologram:
They are devices that produce HD quality holograms which are in continuous horizontal rotation in a power-efficient manner. The device producing these holograms has fans, and on the propeller of these fans, sophisticated RGB light is fixed which produces the holographic illusions on rotating and, interestingly it is used in advertisements for the retail market.
3)Portable holographic device (Holovect):
So, basically, this device produces the world’s thinnest holograms. It is a thousand times thinner than a human hair. This hologram is visible without wearing any special glasses.
It’s also a special type of hologram made of interactive light. We can not only touch but feel it also. They are moving, floating interactive holograms. Isn’t that cool?
Material-fused holograms are holograms that require media for their projection. These holograms can be availed at a low price and can be effectively used to attract customers to shops.
All this, of course in this century sounds fictitious but who knows sitting at your home and at the same time attending a conference in an office maybe is your near future.
So, that’s all. Thanks for reading. Hope we gave you some valuable information.
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