Proposed Telescope Focuses Light Without Mirror Or Lens

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.'"

I discovered that as a kid ..

[Saffaya]

.. when I didn't have my glasses handy and still wanted to look at something in particular.

I would form a small hole by curling my index then look through it for visual correction to my myopea.

Re:This is crazy

[evanbd]

10% of the light from a 30 meter telescope is the same amount of light as a regular 10 meter telescope. Hubble is a 2.4m telescope. I think it will have plenty of light.

Foil doesn't have to crinkle. Look at the center of a mylar balloon -- not exactly crinkly. Obviously if you want telescope-grade not-crinkly you'll have to spend a bit more, but that's not really a problem. This is also a bit more sophisticated than a pinhole camera -- those have trouble collecting much light.

Re:This is crazy

[Genda]

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!

Re:Will they build it.

[hubie]

The gravity probes, as far as I am aware, do not have precisely synchronized flight, but very good knowledge of where each of them are. The science is extracted by measuring the changes in the spacecraft separation (I think the relative distance is known at the tens or hundreds of microns). Flying a separated telescope requires measuring and controlling separations and rotations to a level much more demanding than the GRACE satellites. In principle it can be done now (such as in the lab), but in practice it is very challenging (at least to do on a reasonable budget) which is why many of the NASA and ESA separated telescope projects have been drastically scaled back or delayed (SIM, TPF, Darwin, etc.).

In general, long focal lengths aren't that much of a problem because of the many telescope designs that fold up the optical path.

Re:Looks like a sail...

[Agripa]

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.

The chromatic aberration would be horrible

[exp(pi*sqrt(163))]

The focusing of diffraction gratings is heavily wavelength dependent. The article makes it sound easy to shove in an extra Fresnel lens, but it's not that easy. Maybe it'd be better to use this only as a narrow band imager using suitable filters.

Overall, I like this idea a lot.

Re:Will they build it.

[nusuth]

I'm not sure what you are saying. I read it as a denial that the modern nuke is a fusion weapon. According to the article, the modern nuclear bomb requires a fission trigger. The trigger initiates a fusion reaction, which creates another fission reaction as kind of a happy side-effect. The article states that the largest nuke ever detonated generated a 50Mt blast, which was almost all from the fusion reaction. So while there is fission is going on in the explosion, I would be comfortable saying that the fusion is the main show.

"The largest nuke ever detonated" is not a typical thermonuclear weapon. Its design yield is actually 100 MT and all the surplus comes from the fission of the casing. The bomb was detonated with an inert casing, which halved its actual yield. For almost all other thermonuclear weapons, casing is not inert and the main source of yield energy is fission of the casing. That is the most efficient way to use enriched fuel: You need a certain amount of enriched fuel for primary and you have to have a casing made of a strong and heavy metal. You may as well use non-enriched uranium for the casing, which become fissle when bombarded with neutrons from fusion and doubles the yield for a given amount of enriched fuel. The main show is fusion, but only because it makes the staged thermonuclear weapon possible. The main energy source is still fission.