Science Buddies: "Ask an Expert"

Hello! I was wondering whether it is possible to create a 3D projector according to this:
A high energy light from two projectors passes from both sides of a cylindrical glass container which is filled with fine dust particles suspended in the air. The light ray is illuminated by the dust and if two rays were to intersect at a point, that point would be brighter than the rest. This can be exploited to make several other points to make a 3D object.
My hypothesis could be better explained with a diagram... Any such possibilty??? I wish to give this in the Google Science Fair.

Welcome to the Forum ishanmitra. An interesting idea. It is not a holographic system -- holography is based on interference between mutually coherent light beams rather than simple projection (see the Wikipedia article on holography for all the gory details ). The method you are considering has the advantage that it places fewer demands on the apparatus used than would holography.

I foresee a problem however. I'll denote positions in the image by cartesian coordinates {x, y, z}. Now consider one horizontal slice through your 3-D image, at, say z = 0, and suppose that you wish to illuminate spots at {1,1} and {2,2} (where I have dropped the constant z term from the coordinates within this slice). The first spot requires that beams at x=1 and y=1 be turned on so that their intersection at {1,1} is bright. Similarly the second requires beams at x=2 and y=2 be on. The problem is that now the spots {1,2} and {2,1} will be illuminated brightly, even though these positions are not part of the desired "image" of dots at {1,1} and {2,2}. In a more realistic case of "drawing" a line connecting the two dots, we would have all the beams on over the continuous ranges x = 1 to 2 and y = 1 to 2. The spurious images would now fill a square with corners {1,1}, {1,2}, {2,2}, and {2,1}, which totally obliterates the desired line.

Offhand I don't see a way to fix this problem, but that absolutely does not mean that there is no solution. Goodgle luck!



"I have not failed. I've just found 10,000 ways that won't work."
Thomas A. Edison

Thank you for your reply!
I know that this is not a holograph system, though many use this term as a misnomer for 3D projected imagery.
I already conceived the idea of using diverging rays from both the sides of the glass cylinder, if you know what I mean. For better understanding I posted my diagram as shown below.

The black border represents my glass cylinder. The red lines are actually the light rays which emerge from two points (that will be the light source). They will meet at a point so that only one point will be illuminated hence eliminating the problem you have mentioned. According to this diagram, all points will form an image of a circle. This prototype is having a limitation of creating only a circular image, however this would ensure that I can move on to my next prototype which would be an improvement over this.
What do you think???
I also would like to know the correct apparatus required for this project. What source of light should I use to conduct this experiment? Can I use a projector of some sorts? If so, then can it be programmed through a computer to create images I want?
Waiting for your reply

OK. The diagram really helps. That's clever. Can you make a sphere without crossing rays? (Maybe by time division superposition of 2-D circles within the eye's time of persistence?)

As to apparatus, first let me emphasize that I have NO expertise in optics etc. But what occurred to me was a standard video projector, like those used in projection TV's or, even better, the units used to project images for lectures and other presentations that plug directly into a PC as a remote monitor screen. These can be focused for variable screen distances. If the focus range includes "infinity", i.e. more than 10 m or so, the rays illuminating a pixel on the screen will become parallel effectively, if you see what I mean If the focus range is not adequate, you might need an external lens.

You might want to search for a patent covering this idea.

John Dreher wrote: (Maybe by time division superposition of 2-D circles within the eye's time of persistence?)

Hello again! I didn't exactly understand what you mean by this. A detailed information about this would be better. I understand that you are not much into this and for that I would like to thank you for all the trouble that you have taken to suggest me ways to make this a possibility.

Hi Ishan
I am also working for google science fair project 2014. I think we can collaborate on the topic you have thought about or any other. But the thing is that the project which you are working on is actually available in the market, so if you dont mind we can work together on another area That's related to comp. vision, if you had like.
U may connect with me on fb, my fb username is pulkit.singal.
Regards