Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: neilep on 03/10/2007 16:57:52
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Holograms are great !!..they are my all time favourite 3d light image thingy !
Here's one :
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Nice isn't it ?
But, say I made a hologram of a magnifying glass !!...would the hologram magnifying glass actually work ?
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Do you mean to use it? How would you manipulate it to a place you wanted to look or examine, if it were possible.. How would you produce it and be able to move it around at your convenience?
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BTW what is that a hologram of kind Sir. Is it a replica of a chain of atoms or something..?
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Yes if you make a hologram of a magnifying glass on a transparent piece of glass it will work as a magnifying glass. It will not be as good as a normal one as it is very dificult to make it work for a variety of wavelengths.
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Yes if you make a hologram of a magnifying glass on a transparent piece of glass it will work as a magnifying glass. It will not be as good as a normal one as it is very dificult to make it work for a variety of wavelengths.
That's really fantastic. How it's possible?
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BTW what is that a hologram of kind Sir. Is it a replica of a chain of atoms or something..?
I don't know what it is...I just like the purdy colours !!..LOL..
yes, I suspect it's a molecule or something !!.....and YES...as Dave had said...it seems that a hologram ,if made on thin plastic sheet will act as if it's a real magnifying glass....all you do is move the object in front of the sheet !!
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Yes if you make a hologram of a magnifying glass on a transparent piece of glass it will work as a magnifying glass. It will not be as good as a normal one as it is very dificult to make it work for a variety of wavelengths.
AMAZING !!
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BTW what is that a hologram of kind Sir. Is it a replica of a chain of atoms or something..?
I don't know what it is...I just like the purdy colours !!..LOL..
yes, I suspect it's a molecule or something !!.....and YES...as Dave had said...it seems that a hologram ,if made on thin plastic sheet will act as if it's a real magnifying glass....all you do is move the object in front of the sheet !!
Me too. Thanks, I thought it might be.
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Dave I have seen little thin plastic sheets about the thickness of paper that are actually sold as bookmarks, they to magnify.. is it possible they use this technique for things like that? I saw some a long time ago, but don't recall what the product name was.
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They are called fresnel lenses they have some of the attributes of holograms in that they use small pieces of a curved lens surface to create a very thin lens a hologram would do the same thing but would jump every time the phase had shifted through 360 degrees.
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Thanks.. That does sound familiar!
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But, say I made a hologram of a magnifying glass !!...would the hologram magnifying glass actually work ?
I can interpret your question two ways:
A) you might be asking whether if the magnifying glass was part of a scene, whether in the hologram the magnifying glass acts like a real lens on the objects in the holographic scene.
B) you might be asking whether, if you made a hologram of a magnifying glass object you could somehow use the reconstructed hologram to magnify "real" things.
If you meant (A), then the answer is YES. The hologram reconstructs all the optical properties of the items in the scene. As you move around you'll see the distortion caused by the lens. If you were taking an ordinary 2D photograph of a holographic reconstruction then you even have to set a different focus on the camera for different objects in the scene - just like in real life.
If you meant (B) and your hologram contains a reconstruction of a magnifying glass in the same way as it might contain a reconstruction of a toy car or something (i.e. much the same hologram as A) then the answer is NO. The hologram reconstructs the light that was present when the hologram was made, and cannot act upon objects brought into the reconstruction.
However, it is possible to make a magnifying-glass using holographic principles. What you actually make is a special case of a diffraction pattern which is known as a zoneplate (check out Wikipedia). You can use zoneplate lenses to focus light and even take photographs. As a previous poster mentioned, zoneplates are quite wavelength dependent, so have limitations.
The Fresnel lens is something different again. This is the low-cost (commonly plastic) flat lens often found as a reading-aid (and has lots of rings - which catch the light somewhat distractingly). This has nothing to do with holograms or diffraction though.
Imagine a "plano convex" lens - in everyday-speak this is a magnifying glass which is flat on one side and has a bulge on the other. Now imagine putting that lens on a table, flat side down, and cutting (say 1mm) thick slices off the top of it, cut more slices until you get down to the table top. --Alternatively you could imagine the lens were a bit like the last of the ham in the supermarket, and we're now putting it on the machine and cutting it into thin slices.-- You will now have a stack of 1mm thick circular discs of glass, with a series of diameters. Ignoring the top slice for a minute, the rest of the slices are planar (flat) pieces of glass with just the original surface of the lens remaining at their very edge. This original surface is the only bit that has anything to do with magnifying things - the rest of the slice is just ordinary parallel-sided piece of glass. Now, using a (mental) vertical "bandsaw", cut out the boring flat part of each disk, so each one becomes a ring (a bit like an onion ring). Chuck away all the centres. The outside of each onion-ring is still the original surface of the lens. The inside of the ring is your vertical cut. Now set all your "onion rings" neatly one inside the other on top of a piece of plain glass, and glue down with optical cement. In your mind you have just made a Fresnel lens! (probably Wikipedia has some diagrams)
Real low-cost Fresnel lenses are of course moulded, and the mould may be originally turned (or these days made by a computer-controlled lathe). But I've described the principle - it's just an ordinary lens but with all the glass-that-doesn't-do-much stripped away. They're great for low cost lightweight large lenses, but the optical quality usually leaves much to be desired.
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You can make a zoneplate by photographing the newton's ring pattern that you get when a spherical lens is rested on a flat sheet of glass.
It's all to do with the fact that a lens produces a fourrier transform of an image at its focal plane - and vice versa.
Although a hologram seems like magic, it is , more or less, just a diffraction pattern created when laser light is shone on an object. Then, if you shine laser light on the hologram, the resulting diffraction pattern (image) looks like the original object.
Every piece of the hologram contains some information about the original object - but the smaller the area that you have, the less detail there is in the reconstructed image.
Storing images in holographic form makes the image quite robust in many ways because local damage to the hologram - scratches etc.- have little effect on the quality of the image. They are limited in other ways, though.