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Thin Flat Lenses Could Unleash a Revolution in Space Telescopes

onetimeuse92304 3y ago
Pure BS. The main problem with making optics for telescopes, and especially for large and/or space telescopes is precision. It is hard enough to grind something to a precise shape when that shape is a smooth surface. Forget about making precise fresnel lens that has extremely complex shape that relies on very precise smooth surfaces right next to very sharp discontinuities, that is not going to happen. Another problem is that you don't really ever want lenses for a high power telescope. Lenses cause optical aberration -- and once light rays of different colors go each their own way it is pretty much impossible to put them back precisely enough for the kind of telescope you would want to shoot into space. The article sounds like a third grader got interested in astronomy and suddenly discovered fresnel. Do you think NASA somehow overlooked an obvious solution to all their problems that has been known for hundreds of years to everybody else?
- ithkuil 3y ago
  Have you read https://iopscience.iop.org/article/10.3847/1538-3881/ab2631 https://iopscience.iop.org/article/10.3847/1538-3881/ab2631 and are making a critique of their work or are you talking about the journalist that wrote a piece perhaps dumbing down the concepts a bit too much?
dredmorbius 3y ago
The proposed application for these lenses is for a spectrographic telescope, looking for exoplanet atmospheric biosignatures. See the white paper "Nautilus: A Very Large-Aperture, Ultralight Space Telescope for Exoplanet Exploration, Time-domain Astrophysics, and Faint Objects" (2019) <http://nautilus-array.space/wp-content/uploads/2019/07/Nautilus_Astro2020_WhitePaper.pdf http://nautilus-array.space/wp-content/uploads/2019/07/Nauti...> (PDF) As such, the disadvantages of Fresnel lenses (or for Nautilus, a "multi-order diffractive engineered material lens" or MODE lens) for imaging of objects are largely mooted, as the challenge instead is to gather sufficient quantities of light, in sufficiently short exposure periods, to gather useful spectroscopic data, that is, the light spectrum showing specific absorption lines experienced during planetary transits of their star. From the white paper above: The driver of the design of the Nautilus is to maximize the ratio of sensitivity (light-collecting area and throughput) to cost. The Nautilus combines a simple, non-cryogenic instrument (imager and slitless spectrograph) with a new, lightweight, and low-cost optical element instead of primary mirrors.... Nautilus will use an 8.5m-diameter multi-order diffractive engineered material lens (MODE lens) instead of a primary mirror. These diffractive lenses have ∼100× lower areal density than traditional mirrors, are 100–1,000× less sensitive to misalignments (drastically reducing fabrication and integration costs), and can be cost-effectively replicated (via pressure molding).... Nautilus will use a single instrument, the Nautilus visual/near-infrared imaging spectrograph (NAVIIS). At this point no optical design exists yet for NAVIIS, but in the following we describe the preliminary concept for this instrument. NAVIIS will utilize a dichroic mirror to split the incoming light into the visible light (NAVIIS-VIS, 0.5–0.95 μm) and near-infrared (NAVIIS-NIR, 0.95–1.7 μm) channels.

Pure BS. The main problem with making optics for telescopes, and especially for large and/or space telescopes is precision. It is hard enough to grind something to a precise shape when that shape is a smooth surface. Forget about making precise fresnel lens that has extremely complex shape that relies on very precise smooth surfaces right next to very sharp discontinuities, that is not going to happen. Another problem is that you don't really ever want lenses for a high power telescope. Lenses cause optical aberration -- and once light rays of different colors go each their own way it is pretty much impossible to put them back precisely enough for the kind of telescope you would want to shoot into space. The article sounds like a third grader got interested in astronomy and suddenly discovered fresnel. Do you think NASA somehow overlooked an obvious solution to all their problems that has been known for hundreds of years to everybody else?

ithkuil 3y ago
Have you read https://iopscience.iop.org/article/10.3847/1538-3881/ab2631 https://iopscience.iop.org/article/10.3847/1538-3881/ab2631 and are making a critique of their work or are you talking about the journalist that wrote a piece perhaps dumbing down the concepts a bit too much?

dredmorbius 3y ago

The proposed application for these lenses is for a spectrographic telescope, looking for exoplanet atmospheric biosignatures. See the white paper "Nautilus: A Very Large-Aperture, Ultralight Space Telescope for Exoplanet Exploration, Time-domain Astrophysics, and Faint Objects" (2019) <http://nautilus-array.space/wp-content/uploads/2019/07/Nautilus_Astro2020_WhitePaper.pdf http://nautilus-array.space/wp-content/uploads/2019/07/Nauti...> (PDF) As such, the disadvantages of Fresnel lenses (or for Nautilus, a "multi-order diffractive engineered material lens" or MODE lens) for imaging of objects are largely mooted, as the challenge instead is to gather sufficient quantities of light, in sufficiently short exposure periods, to gather useful spectroscopic data, that is, the light spectrum showing specific absorption lines experienced during planetary transits of their star. From the white paper above: The driver of the design of the Nautilus is to maximize the ratio of sensitivity (light-collecting area and throughput) to cost. The Nautilus combines a simple, non-cryogenic instrument (imager and slitless spectrograph) with a new, lightweight, and low-cost optical element instead of primary mirrors.... Nautilus will use an 8.5m-diameter multi-order diffractive engineered material lens (MODE lens) instead of a primary mirror. These diffractive lenses have ∼100× lower areal density than traditional mirrors, are 100–1,000× less sensitive to misalignments (drastically reducing fabrication and integration costs), and can be cost-effectively replicated (via pressure molding).... Nautilus will use a single instrument, the Nautilus visual/near-infrared imaging spectrograph (NAVIIS). At this point no optical design exists yet for NAVIIS, but in the following we describe the preliminary concept for this instrument. NAVIIS will utilize a dichroic mirror to split the incoming light into the visible light (NAVIIS-VIS, 0.5–0.95 μm) and near-infrared (NAVIIS-NIR, 0.95–1.7 μm) channels.