Naked Science Forum
Non Life Sciences => Technology => Topic started by: Jolly on 15/12/2015 00:07:40
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So I am looking into hologram Technology.
Want to build a hologram on a table, and was just wondering, if anyone here has any know how about, free standing hologram production?
I'm just going to experiment basically till something works.
So how many different ways can holograms be produced? and with each what is the process by which they function?
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Here is a simple explanation to get you started. Physics gurus, please excuse the artistic license used here to make the process simple and accessible.
To make a hologram you usually need a laser. This produces light waves that are all in-step with each other; this is known as "coherence". In essence, the waves leaving the laser are all the same size and are all in sync; this means that all of the peaks and troughs of the waves line up with each other.
The first step is to pass the light beam through a "splitter". This is a half-silvered mirror that lets some of the light through and reflects the rest. The result is that you now have two light beams.
One of these beams you shine directly at your target, which is a piece of photographic film or a light-sensitive sensor. This is called the reference beam.
The other beam you shine at the object you want to turn into a hologram; this is the "object beam".
Light reflected off the object is then also directed onto the photographic film or sensor.
Now, although both beams of light - the reference and the object - were in-step when they left the laser, the object beam has travelled a different distance compared with the reference beam, because it has been reflected off the object along the way.
This means that when they reach the photographic film, the two beams of light are now no-longer "in-step". In some places, some waves will arrive going up (to a peak) and meet other waves arriving going down. In these places they will cancel out, producing a dark spot. In other places, both waves will both be going upwards or downwards towards a peak or trough; here they add together and produce a bright spot. This is called interference and gives rise to a pattern of tiny "fringes" of light information on the photographic plate. These fringes correspond to the structure of the object's surface that reflected the object light beam.
Now, when normal light, or another laser beam, falls on these patterns of fringes, they re-create a visual impression of the surface structure that produced them in the first place; this is the hologram.
As I say, a very simple explanation to get you started. Perhaps the others here can embellish to add some meat on these bones.
Chris
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The photographic plate may be more of a problem than it used to be, since the mass-market chemical film companies are now defunct.
Most of the interference fringes described by Chris are very small - on the order of a wavelength of light. So for best results you need very high resolution photographic film. For a good 3D effect, you need a large sheet of film. While X-Ray film is very expensive, a quick search suggests there are suppliers of specialist holographic film.
The cheapest cameras are those on our smartphones. However, the pixels on these cameras are many times the wavelength of light, and the lens is very small, so you will get very little 3D effect.
Exposing a large sheet of film with a small laser takes a long time. The subject and film must be held very still, or the tiny fringes will be blurred. Some people use higher-powered lasers, but be careful of your eyes - use lenses to spread the laser beam over the whole object and film, and use the right type of safety goggles.
It would be ironic if you ended up with a great hologram that you can't appreciate because your vision has been destroyed in one eye .
See: http://en.wikipedia.org/wiki/Holography
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Want to build a hologram on a table,
Let me know how you get on. I want to make an holographic system for looking at Chladni vibration patterns. It looks as though I will need similar components to yours but lower power laser and hope for direct digital capture.
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Chladni vibration patterns
What are they?
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Here is a simple explanation to get you started. Physics gurus, please excuse the artistic license used here to make the process simple and accessible.
To make a hologram you usually need a laser. This produces light waves that are all in-step with each other; this is known as "coherence". In essence, the waves leaving the laser are all the same size and are all in sync; this means that all of the peaks and troughs of the waves line up with each other.
The first step is to pass the light beam through a "splitter". This is a half-silvered mirror that lets some of the light through and reflects the rest. The result is that you now have two light beams.
One of these beams you shine directly at your target, which is a piece of photographic film or a light-sensitive sensor. This is called the reference beam.
The other beam you shine at the object you want to turn into a hologram; this is the "object beam".
Light reflected off the object is then also directed onto the photographic film or sensor.
Now, although both beams of light - the reference and the object - were in-step when they left the laser, the object beam has travelled a different distance compared with the reference beam, because it has been reflected off the object along the way.
This means that when they reach the photographic film, the two beams of light are now no-longer "in-step". In some places, some waves will arrive going up (to a peak) and meet other waves arriving going down. In these places they will cancel out, producing a dark spot. In other places, both waves will both be going upwards or downwards towards a peak or trough; here they add together and produce a bright spot. This is called interference and gives rise to a pattern of tiny "fringes" of light information on the photographic plate. These fringes correspond to the structure of the object's surface that reflected the object light beam.
Now, when normal light, or another laser beam, falls on these patterns of fringes, they re-create a visual impression of the surface structure that produced them in the first place; this is the hologram.
As I say, a very simple explanation to get you started. Perhaps the others here can embellish to add some meat on these bones.
Chris
Thanks Chris That process creates a holographic picture. That is not the area I am looking into, I am trying to find a way to follow the example of holographic Television. And create free standing holograms that we can interact with.
I intend to cheat slightly. I am mean basically with a few motion senors, that track what you are doing and a computer program- you'll interact with empty space in the real world, but an actual object in the computer world. What I am interested in finding a way to fill that empty space with a holographic image, I could uses a 3d projector and glasses- but there are eye strain issues and I'd prefer not needing glasses or a 3d projector.
I know in japan using lazers and gasses they have managed to create holograms- but it's rather dangerous and you certainly can't touch them.
So I am looking at how to either convience the brain that the image it's seeing is in 3d when it isnt, Or a way to get enought displacement from different projects, maybe using a few layers of glass and mirrors, to actually generate a holographic image- Gonna start small and try to get the game Pong to work- then maybe holographic Pool. It's the plan anyway.
Maybe peppers ghost has an answer. Or Smoking [:D]
45 degree glasses? If you had glasses that made any image present itself at 45 degrees in the glass, the images could appear as a hologram.
Peppers Ghost glasses? Anyone?
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Want to build a hologram on a table,
Let me know how you get on. I want to make an holographic system for looking at Chladni vibration patterns. It looks as though I will need similar components to yours but lower power laser and hope for direct digital capture.
Well how do you want to present them? Just as a hologram? You could simply make the pyramid system they use on I-phones, you'll have to explain exactly what you are looking to achieve, if that is not good enough to represent them.
Here is a simple video explaining how to make smart phone pyramids.
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Chladni vibration patterns
What are they?
They are patterns of nodes and antinodes on a vibrating surface. They are particularly useful when looking at the vibrational modes and resonances of musical instruments. Usually they are made by putting a fine powder on a vibrating surface eg instrument soundboard, getting it to vibrate at various frequencies, the powder then moves to the nodes showing how the surface is vibrating.
This works ok for flat surfaces eg guitar soundboards, but curved surfaces are a problem. Laser techniques can show the nodes and antinodes as interference patterns.
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Well how do you want to present them? Just as a hologram?
No, as an interference pattern. Method of creation is very similar.
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Well how do you want to present them? Just as a hologram?
No, as an interference pattern. Method of creation is very similar.
Not sure I entirely understand you mean you want to produce a hologram by creating an a lazer light interference pattern generated in a similar way?
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Not sure I entirely understand you mean you want to produce a hologram by creating an a lazer light interference pattern generated in a similar way?
When you create your hollogram you will split the laser beam into one illuminating the subject and a reference beam, however you aren't trying to produce a photo so you wont use a lens in front of the recording film.
I will also split the beam, but the light from the subject will be focussed via a camera lens as I need a photo. There are a number of ways of doing this which I intend to experiment with, but they all rely on the fact that if the surface of the instrument moves there will be a difference in phase between the illuminating and reference beams and hence a pattern showing which parts of the surface are moving and which are stationary.
Best of luck with your project
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actually generate a holographic image
I take it that you are proposing to generate the holographic fringe pattern computationally, and then project this so that the human visual system sees the object that was generated by the computer?
The computer model must include the object to be modeled (a 3D version of Pong, in this case), the position of the human in relation to the screen and the laser illuminator.
The image will appear in a space between the eyes and the area of the screen.
As in the Youtube video, you can make some significant simplifying assumptions:
- A normal hologram contains fringes that will direct light to all viewers in all directions, which is a huge amount of information which involves a huge amount of computation and storage. What you want to do (at least initially) is to direct the light to just 2 eyes, fixed in just a single position.
- By using a very low resolution object (a blocky Pong bat and ball), you don't need to generate and store fringes from every hair on a possum (for example).
- By initially generating a still image, you can generate the image offline, and just display it. Playing Pong in real time means generating fringes 25-50 times per second, which is a huge computational burden.
- A 1-viewer still image is a lot easier than a 2-player game + audience!
What I don't know is:
- how fine the fringes need to be for a coarse resolution object. There is a convention about the highest visual resolution that can be seen by the human eye (dubbed by some a Retina display). Holographic fringes can make use of much higher resolution than this!
- How you could arrange a polarized laser to work with a display that is usually backlit by non-polarized light.
As an algorithm, I suggest that you try ray-tracing (http://en.wikipedia.org/wiki/Ray_tracing_(graphics)), starting from the human eye location, and working backwards to the (virtual) object to determine where the laser would project fringes on a photographic plate.
Bear in mind that generating a holographic image is far more computationally demanding than conventional ray-tracing, since you don't just trace one ray to generate the amplitude of 1 pixel of the virtual object. You must add up the amplitude and phase of every ray from every pixel on the virtual object in order to generate the amplitude of 1 pixel on the holographic screen. It requires many orders of magnitude more computation than conventional ray-tracing! It should be possible to speed this up with parallel GPU computers, such as in modern games consoles.
In fact, it may be better to calculate the wavefront (amplitude + phase) that you would get from every pixel on the object, and just sum the wavefronts from every pixel on the object to generate the amplitude and phase at every point on the screen.
In any case, I think it will be quite a few years before anyone at home is using their Christmas present to play Holographic Halo!
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actually generate a holographic image
I take it that you are proposing to generate the holographic fringe pattern computationally, and then project this so that the human visual system sees the object that was generated by the computer?
Well that maybe be an opition, really I am looking at different ways you could represent a game, like pool in holographic form it doesn't actually have to be a hologram, something like the peppers ghost effect could also work, but a game you can psyically interact with in the real world- not on a screen.
Bascially as an example you find a basic pool game program, and combine it with a spacial awareness sensor system, Cameras view the real life, probably Glass table, and with a sensor on the cue tip as a single point of interaction with the game space, and you put these together. Basically end up with pool you play on the table using the sensors, and the in the computer at the same time. The question is finding a way to get the balls to appear in a holographic form. Where I am, they already have a touch screen intereactive games table, I have to fix it and that's in progress, but I am hoping to add a holographic system to it.
The glass touch screen table surface works with sensors that see where you are touching, and has a mirror that reflects images from an underneath projector- that's already made, it broke recently, but it does work. I could now up load a pool game onto it and add the programming to simply touch screen, the hit the balls with fingers. But I would rather add a sensor to a cue tip and play in 3d space.
That is not soo complicated, it's a lot of work programming ect. Bigger question how do you get the balls to appear in 3d form, holographically, over the table.