First flat telescope lens that captures color, detecting light from stars

https://phys.org/news/2025-02-flat-telescope-lens-capture-faraway.html

by wglb • 1 year ago

87 25 1 year ago

wglb• 1 year ago

Applied Physics Letters: https://pubs.aip.org/aip/apl/article/126/5/051701/3333379/Co...

I really think they could have done better with `Visualization3.mp4`. The black and white ICCapture screen recording of an LED light (?) doesn't really do a whole lot to show off the achromatic capabilities of their lens.

nowittyusername3• 1 year ago

I hope they point it at the night sky and see a green star. That would be a very exciting event, as naturally green stars are not possible. I know that if I was an advanced "angler fish" type of civilization, that's definitely the lure I would use in a dark forest universe. on that note i hope the scientists are not stupid enough to send a signal to that star.

poulpy123• 1 year ago

Why would they detect a green star ?

amenghra2• 1 year ago

Some stars, eg Lambda B, do appear green when looking thru amateur telescopes.

adrian_b2• 1 year ago

Most likely they appear blue-green (a.k.a. turquoise a.k.a. teal), not green.

As another poster has mentioned, with increasing temperatures the color sequence for a black body is black => red => yellow => white => blue-green => blue.

Neither the greenish colors intermediate between yellow and blue-green nor the purplish colors intermediate between red and blue can appear as colors of a hot body, but only the colors that can be seen when low-pass filtering white light (i.e. between red and yellow, inclusive) or when high-pass filtering white light (i.e. between blue-green and blue, inclusive).

While above I have simplified by saying that purplish colors should not appear, that is only partially true, because very hot stars could appear as violet, i.e. reddish blue, due to the defect of human vision that the red photoreceptors are sensitive not only to red light, but also to light with a higher frequency than where the maximum sensitivity for blue is, so the high-frequency violet light excites both the blue and the red photoreceptors, being indistinguishable from a mixture of blue light with low-frequency red light.

With a video camera where the output signals would not be processed in such a way as to mimic the bugs of human vision (like in all normal color video cameras), purplish colors would not be obtained for hot bodies.

hnuser1234563• 1 year ago

It's not really possible to make a green star because the color is mostly just determined by the temperature, with colder stars being redder and hotter being blue. A green star would just be a white star, or a star with the same temperature as the sun, whose peak output is in the green range, but having almost equal amounts of light in the blue and red range, appearing white. There is no way to "squish" the black body spectrum into a narrower range, it is determined by the Maxwell–Boltzmann distribution of velocities of particles in a gas.

nowittyusername3• 1 year ago

That's my point. A green star would signal to anyone in the universe that something is really off here and most likely achieved by unnatural means (aka and advanced civilization). This would attract attention. which the civilization that sent the beacon can take advantage of for various reasons. There are many such beacons that could be placed all over the universe to attract attention.

Synaesthesia2• 1 year ago

How does it work?

wolfi1• 1 year ago

seems to me it's a Fresnel Lens, unfortunately the article is behind a paywall to say more

laasworld• 1 year ago

Here's a decent open-access review: https://doi.org/10.3390/sym16101377

The key point is that the sub-wavelength nature allows broader wavelength behavior and is distinct from conventional fresnel lenses. I suspect these plastic lenses will never be as sharp as a conventional lens, but presumably loads better than fresnel lenses and presumably worth it for weight-/size-restricted applications.

novosel• 1 year ago

"The key innovation lies in the microscopically small concentric rings that the researchers can pattern on the substrate. Unlike the ridges of FZPs (Fresnel Zone Plate), which are optimized for a single wavelength, the size and spacing of the flat lens' indentations keep the diffracted wavelengths of light close enough together to produce a full-color, in-focus image."

Synaesthesia2• 1 year ago

Yeah I read that, and upon re-reading it I have some vague idea on how that might work, but I would still need to read the paper and see some illustrations to really get it.

Sounds like this may enable full-colour astrophotography (always wondered why it's all in B&W!) and/or make achromatic telescopes a lot lighter.

ZeWaka• 1 year ago

If you look at the supplementary information document, there's more pictures.

There's definitely quite a haze around light sources. It seems they have tried applying some deconvolution to try to increase the sharpness, but the resulting images are still quite muddled.

Here's one of the libraries they used: https://github.com/apsk14/rdmpy

floxy• 1 year ago

f/2. I wonder why they went with such a short focal ratio. Something inherent with Fresnel lenses?

smusamashah• 1 year ago

There is a related article from 2020 linked at bottom about flat lens cameras

https://phys.org/news/2020-03-focus-free-camera-flat-lens.ht...

It says it can focus everything at once. I don't understand how this works either but these two are probably similar science.

First flat telescope lens that captures color, detecting light from stars

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