Interferometer Device Sees Text from a Mile Away

https://physics.aps.org/articles/v18/99

by bookofjoe • 1 year ago

263 62 1 year ago

physics.aps.org

ck2• 1 year ago

My favorite "lasers at distance" thing will be when amateurs can get a few photons back from the mirrors left on the moon

https://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment...

Not quite there yet at the amateur level, private industry soon, but then there is the question of safety to air traffic.

Can you imagine the first moon data link? JWST has 8mbps

eesmith• 1 year ago

People do use radio (though not optical) for Earth-Moon-Earth data links: https://en.wikipedia.org/wiki/Earth%E2%80%93Moon%E2%80%93Ear...

IAmBroom3• 1 year ago

And the next will be when the amateur data links manage to noticeably heat the mirrors...

Calwestjobs3• 1 year ago

they will heat starlink first.

vmh1928• 1 year ago

Modulating a laser beam for communications is not new but this distance effort by amateurs doing a two-way voice transmission over 167km in New Zeland is pretty cool. This article also mentions a number of other laser communication long distance efforts.

https://www.modulatedlight.org/Modulated_Light_DX/MODULATED_...

knotimpressed• 1 year ago

I wonder if the requirement to rotate the target is inherent, or if it could be optimized away eventually?

xnx2• 1 year ago

Or rotate the telescopes

IAmBroom3• 1 year ago

... which are radially symmetric.

stevemadere• 1 year ago

I suspect this was an easy way to test it without having to build a rotatable optical bench.

A practical device may be an array of light sources and telescopes on a rotating mount or a set of moveable mirrors that achieve the same effect.

nkrisc• 1 year ago

If it is required, then in a real application you could just rotate the laser array instead.

Noumenon72• 1 year ago

I also wonder about the requirement for the letters to be made of reflective material.

27theo• 1 year ago

The team demonstrated that this intensity interferometer can image millimeter-wide letters at a distance of 1.36 km

Calwestjobs3• 1 year ago

intensity interferometer means it interferometers intensity of light.

imaging technologies you mistook for imagination technologies and their gpu inside of a sega dreamcast or iphone, ipad,...

1.36 km = 0.85 miles

abcd_f• 1 year ago

Letters were 8 mm.

To demonstrate the system’s capabilities, the team created a series of 8-mm-wide targets, each made from a reflective material and imprinted with a letter.

hannasanarion• 1 year ago

I checked the paper, by "8mm wide" they mean that the letters were 8mm tall, which is a 22pt font (name-tag size), for those curious.

mturmon• 1 year ago

1mm at 1.36 km works out to about 150 milliarcsec (mas), if you're used to those units from astronomy contexts.

croisillon• 1 year ago

i'm a bit confused when they don't measure things in olympic pools and bananas for scale

IAmBroom3• 1 year ago

OK, this part was brilliant:

"To avoid this problem, the team divided their 100-milliwatt laser into eight beams. Each beam travels along a slightly different path through the turbulent atmosphere and thus receives a different random phase perturbation. Counterintuitively, this incoherent illumination makes the interference effects observable.

When I first started studying optical engineering, my teacher had worked on the first under-the-RADAR guidance system for bombers. He told lots of amusing stories, like how the pilots insisted on a manual override - so they "agreed" to provide a switch, noting to us manual piloting at near-treetop level and 1,000 ft/s is insane.

He taught us about the nominal amount of turbulence in the atmosphere, and that it limited space-based cameras to about half a foot resolution - a limit he said couldn't be broken. Therefore, license plates would never be readable from space...

Before I was out of grad school, they had broken it with laser techniques on nearby targets. Flash the laser at the same time as the image, scan the laser-illuminated spot, calculate the perturbance, and reverse-filter the image. A lot of processing (for that day), but it could be done back on Earth.

As you can see from the test images, the 8 lasers aren't enough to perfectly smooth out the noise. The noise is probably square-root-8 improved, so resolution should improve by a factor of not quite 3. Move those lasers slightly and repeat 12 times; you've improved resolution by 10. This is easy to do quickly; you should be able to read fine print held by a car passenger on the highway.

perihelions• 1 year ago

- "Flash the laser at the same time as the image, scan the laser-illuminated spot, calculate the perturbance, and reverse-filter the image"

That's also how some adaptive optics work in astronomy,

https://en.wikipedia.org/wiki/Laser_guide_star

embwbam• 1 year ago

The adaptive optics system for the DKIST solar telescope actually deforms each point of the mirror at 60Hz or something to do wavefront correction!

kevmo314• 1 year ago

That's how night mode works on Pixel phones, right? I believe it takes a few images in rapid succession and took advantage of the noise being random which meant a high quality image under a noisy sensor with some signal processing.

Calwestjobs3• 1 year ago

some phones shine IR floodlight, too.

picture• 1 year ago

Integrating over a longer time to get more accurate light measurements of the a scene has been a principal feature of photography. You need to slow down the shutter and open up the aperture in dark conditions.

Combining multiple exposures is not significantly different from a single longer exposure, except the key innovation of combining motion data and digital image stabilization which allows smartphones to approximate longer exposures without the need of a tripod.

jfarlow• 1 year ago

It also can actually allow you to identify positions within the image at a greater resolution than the pixels, or even light itself, would otherwise allow.

In microscopy, this is called 'super-resolution'. You can take many images over and over, and while the light itself is 100s of nanometers large, you actually can calculate the centroid of whatever is producing that light with greater resolution than the size of the light itself.

https://en.wikipedia.org/wiki/Super-resolution_imaging

Daub• 1 year ago

This is how we reduce noise in filmmaking. My de-noise node in DaVinci has two settings: spatial and temporal. Temporal references 3 frames either side of the subject frame.

hammock3• 1 year ago

He told lots of amusing stories, like how the pilots insisted on a manual override - so they "agreed" to provide a switch, noting to us manual piloting at near-treetop level and 1,000 ft/s is insane.

You ought to read Tom Wolfe’s “the right stuff” asap if you haven’t already

bookofjoe• 1 year ago

And watch this video of Neil Armstrong nearly getting killed when his test flight of a lunar lander trainer (on Earth) crashed and burned:

https://youtu.be/tUJDbj9Vp5w?si=YFeau8vskUvpDUNV

dekhn• 1 year ago

We are in the middle of a renaissance of image processing across a wide range of fields. Many of the previous limits are being smashed by using new materials and algorithms. See https://en.wikipedia.org/wiki/Fourier_ptychography for an example

nereye• 1 year ago

Applied Science YT channel has an interesting video showing this at work:

Dramatically improve microscope resolution with an LED array and Fourier Ptychography

https://www.youtube.com/watch?v=9KJLWwbs_cQ

globnomulous• 1 year ago

Wow, I had no idea. I know nothing about the field, so maybe someone better educated can answer my innocent, probably naive question: my instincts tell me that any technology that makes humans better at manipulating or interpreting light has vast potential to alter our lives. Is that right?

quantadev• 1 year ago

So what's the summary of how this works? I don't think it was explained well, and I'm fairly up to speed with the physics of photons etc. Is it that the multiple lasers are able to destructively interfere with each other so that they cancel out the noise from each other since the noise will be the same in all of them? That's tricky because if the photons are phase shifted to cancel out the noise that seems like the ENTIRE laser signal would be cancelled out too. Maybe this is what's happening, and the only thing "left over" is the signal from the source (what's being measured)?

admash• 1 year ago

Presumably this could be used for color imaging by using lasers of different wavelengths?

jdiff• 1 year ago

I believe it'd be pretty wonky coloring, or at least it could be, since it'd be capturing snapshots of individual frequency responses. If something is visibly green, reflecting across most of the greenish areas of spectrum, but happens to absorb the exact frequency of the laser, it'd appear black when imaged this way. Or at least not green.

echoangle• 1 year ago

I think that’s the case for regular cameras too though, the filter for the pixels doesn’t exactly replicate the response of the cones in the eyes either, right? So you have things where the camera sees a different color than a human eye.

kulahan• 1 year ago

If it’s truly just like the methods astrophysicists use for transit imaging, you might even be able to do some funky stuff like monitor invisible gasses. Could potentially be revolutionary for things like fume safety and viral spread tracking, among other uses. Might even be able to analyze liquids in a container without having to touch the liquid (the name for this type of testing evades me at the moment)

1minusp• 1 year ago

i think the applications to spy-craft could be quite interesting here. Something for the next mission impossible movie maybe?

aerostable_slug• 1 year ago

It's also interesting to consider that they may be reinventing prior classified research.

greggsy• 1 year ago

Trivial to eliminate through window treatments and training to mitigate should-surfing risks.

It’s probably more valuable as a surveillance and monitoring tool than an espionage one, but they would no doubt be the first customers (if not already).

erikerikson• 1 year ago

How does this compare to the state of the art?

hammock3• 1 year ago

Lasers really are an underrated miracle. So many diverse uses for things that would be impossible without them.

And we are about to be saturated in them as soon as LiDAR full self driving goes mainstream

vinkelhake• 1 year ago

LIDAR pulses are in the order of a few nanoseconds.

hammock3• 1 year ago

How many pulses per second?

therein• 1 year ago

Matter-wave lasers coming soon.

krige• 1 year ago

wave motion lasers just right after!

codeulike• 1 year ago

... but only if its written on shiny paper

mrexroad• 1 year ago

He imagines that the remote-imaging system could have several applications, including monitoring insect populations across agricultural land.

“Insect populations” is a funny way to spell secrets. Jokes aside, it does seem like this could serve a wide range of non-espionage related use cases. Really cool.

metalman• 1 year ago

there is a now old technology where a laser is shone on a window, and the resulting glow is imaged, the images if anylised are an analog audio signal that is created by voices inside a building vib the newer version under discussion here is a direct fit forthe same use, but at much greater distances and greater fidelity/resolution there were many,mostly mechanical devices, made to detect aircraft ,deployed durring WWII, that had two large acoustical horns directed a central binaural detection sensor, the whole aparatus was the mounted on a large stage that turned, and the horns were also aimable, giving a bearing, and speed on aircraft, in dark ,coudy, or other conditions.The inferometer bieng someone in a seat.

unyttigfjelltol• 1 year ago

That interesting article led me down a research rabbit hole of microwave maser inferometers and whether that could be an explanation for the controversial Havana Syndrome. And, having skimmed descriptions of historical SIGINT projects Buran[1] and Luch[2], and the theoretical advantages of such a system ... my curiosity in Faraday cages is renewed.

[1]https://en.wikipedia.org/wiki/Laser_microphone

[2]https://en.wikipedia.org/wiki/Olymp-K

bzmrgonz• 1 year ago

the reflective material requirement seems to be a limiting factor, so most likely application would be license plate reading?? They didn't mention anything about moving targets, but I guess space debris is also moving so maybe as an added layer to LiDAR??

mcswell• 1 year ago

My (mis?)understanding was that two receivers acting as an interferometer can only resolve things that are on a line parallel with the line between the receivers--so if the receivers are on a horizontal, then they can resolve left and right in their targets, but not up and down. But the images shown in the paper have more or less full 360 degrees resolution. Is that because they rotated the target? The paper says they did, but it's not clear how many increments of partial rotation they did--every 10 degrees, 20,...

If the target cannot be rotated, can the two (or more) receivers revolve around a central axis? If so, presumably one of the receivers could revolve around the other (fixed) receiver to the same effect.

roschdal• 1 year ago

Except when it's raining

alexalx666• 1 year ago

the website delights with the absence of ads throwing up into my eyes

grues-dinner• 1 year ago

Use Firefox and Unlock Origin and that can be every website, even on mobile.

Interferometer Device Sees Text from a Mile Away

Related Stories