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Proposed Telescope Focuses Light Without Mirror Or Lens

Posted by Soulskill on from the i-can-see-clearly-now dept.

A team of scientists from Observatoire Midi Pyrénées in Toulouse, France have been working with an unusual technique for focusing light. It takes advantage of diffraction - the bending of waves when they encounter an obstacle in their path - to focus light as it passes through a foil sheet with precise holes in it. The scientists suggest that an orbital 30-meter imager could resolve planets the size of Earth within 30 light-years. In addition, the foil is much lighter than traditional materials, and thus easier to transport. "A Fresnel imager with a sheet of a given size has vision just as sharp as a traditional telescope with a mirror of the same size, though it collects just 10% or so of the light. It can also observe in the ultraviolet and infrared, in addition to visible light. The imager can take very detailed images with high contrast, which is great for 'being able to see a very faint object in the close vicinity of a bright one.'"

7 of 165 comments (clear)

  1. Looks like a sail... by sapphire+wyvern · · Score: 4, Interesting

    Hmm, a large flat surface with holes in it.

    It looks like launching one of these babies would require solutions to the same technical problems as solar sails, ie stowing & unfolding once in orbit.

    Would it be possible to have the sheet do double duty, acting as both a Fresnel "lens" and a means of propulsion for the spacecraft? That might be a neat way of getting the instruments to a good location.

    1. Re:Looks like a sail... by Agripa · · Score: 3, Informative

      You can build ground based radio telescopes or satellite antennas using this technique. I have an old Radio Electronics with an article and plans for a greater than 4 foot refraction based satellite antenna using concentric strips of plywood with the focus behind the flat surface. The advantage lies in not having to form a curved three dimensional surface. The math is relatively straightforward.

      The difference with the space based proposal is using optical wavelengths instead of radio wavelengths so the edge spacing is much smaller.

  2. ok... by fyngyrz · · Score: 4, Insightful

    Make a sphere with a central axis. Place the fresnel lens on the surface of the sphere. Rotate the sphere about the center (where the focal point is.) No more formation flying, etc. Since you don't need any part of the sphere but the place where the fresnel lens is, just create a radius - lens at one end, focal point at the other end. Use a track to adjust the focal point distance from the foil. Rotate the entire assembly to re-point. No formation flying. Precision alignment all the time. Slow adjustment means good fuel economy.

    It seems to me that this is a great excuse for a foil-making plant in space. Imagine a veewwwwy large foil sheet. Then think of the available resolution. This is better than a dispersed array.

    Well, one can hope. :-)

    --
    I've fallen off your lawn, and I can't get up.
  3. Problems by FearForWings · · Score: 4, Funny

    I think it would be clear to anyone who examines it, the idea clearly has some holes in it.

    --
    I don't know about angles, but it's fear that gives men wings. -Max Payne
  4. Not for amateurs... by syousef · · Score: 4, Interesting

    I was thinking hey neat till I read this in the article.

    For one thing, the light comes to a focus far away from the foil sheet - with distances measured in kilometres, which means the camera and other instruments have to be mounted on a separate spacecraft. The instrument spacecraft would have to stay precisely aligned with the foil sheet, to within a millimetre or so.

    Certainly not impossible, and still exciting, but this isn't going to be a mainstream or amateur tool any time soon.

    Looks like there also may be a related patent to get past...

    http://www.patentstorm.us/patents/6375326-claims.html

    --
    These posts express my own personal views, not those of my employer
  5. more fun with diffraction by heeeraldo · · Score: 3, Interesting

    Canon has been using the same principle in a couple of lenses for some time now. The lenses themselves are pretty damn expensive but well regarded; I hope the telescope meets similar success.

  6. Re:This is crazy by Genda · · Score: 4, Informative

    This is actually a really clever solution to a number of thorny problems. The first being, how do you get a really big telescope into space without breaking the bank??? Another being how do you get great contrast to show up faint sources?

    1. A) Not a Pinhole camera, It uses difraction caused by wave interaction through the holes of the lense.
    2. B) The lens has an aperture of 30 meters, with a surface area of over 700 Square meters. Even at 10% transmission, it would have more than 15 time the light gathering power of the Hubble, and more than 150 times the resolution.
    3. C) The best way to transport the lense would be to wrap the foil on a cylindrical spindle keeping it free of wrinkles, then having it unwound onto some kind of frame for mounting and stretching.
    4. D) It would have to be placed in some kind of protection housing to prevent damage from space debris.
    5. E) It would have to use some kind of laser/optical alignment system to get the lense and camera operating in conjunction. However this is not a big problem, long baseline interferometry in space would require much stricter positioning for constellations of satellites and such devices are already on the drawing boards.

    In short, this is a perfectly viable technology, and it poses a fascinating solution to a really challenging problem.

    Bravo!