[HN Gopher] Interferometer Device Sees Text from a Mile Away
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Interferometer Device Sees Text from a Mile Away
Author : bookofjoe
Score : 255 points
Date : 2025-05-10 14:05 UTC (5 days ago)
(HTM) web link (physics.aps.org)
(TXT) w3m dump (physics.aps.org)
| ck2 wrote:
| 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 wrote:
| 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...
| IAmBroom wrote:
| And the next will be when the amateur data links manage to
| noticeably heat the mirrors...
| Calwestjobs wrote:
| they will heat starlink first.
| vmh1928 wrote:
| 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 wrote:
| I wonder if the requirement to rotate the target is inherent, or
| if it could be optimized away eventually?
| xnx wrote:
| Or rotate the telescopes
| IAmBroom wrote:
| ... which are radially symmetric.
| xnx wrote:
| I recognize the ambiguity, but was referring to the
| orientation of the telescope system to the target.
| stevemadere wrote:
| 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 wrote:
| If it is required, then in a real application you could just
| rotate the laser array instead.
| Noumenon72 wrote:
| I also wonder about the requirement for the letters to be made
| of reflective material.
| 27theo wrote:
| > The team demonstrated that this intensity interferometer can
| image millimeter-wide letters at a distance of 1.36 km
| Calwestjobs wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 1mm at 1.36 km works out to about 150 milliarcsec (mas), if
| you're used to those units from astronomy contexts.
| croisillon wrote:
| i'm a bit confused when they don't measure things in olympic
| pools and bananas for scale
| IAmBroom wrote:
| 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 wrote:
| - _" 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 wrote:
| The adaptive optics system for the DKIST solar telescope
| actually deforms each point of the mirror at 60Hz or
| something to do wavefront correction!
| pfdietz wrote:
| Big telescopes have to actively deform the primary mirror
| anyway, just to keep it in proper shape as it moves around
| under gravity loads.
| kevmo314 wrote:
| 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.
| Calwestjobs wrote:
| some phones shine IR floodlight, too.
| picture wrote:
| 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.
| tonyarkles wrote:
| I agree with you wholeheartedly and just want to add one
| more aspect to this: it _also_ allows you do handle the
| case where the subject is moving slowly relative to the
| camera. Easy example is taking long exposures of the moon
| from a tripod. If you just open the shutter for 30 seconds
| the moon itself is going to move enough to cause motion
| blur; if instead you take a series of much faster photos
| and use image processing techniques to stack the subject
| (instead of just naively stacking all of the pixels 1:1)
| you can get much better results.
| magicalhippo wrote:
| For bright stuff like the moon, it's my understanding the
| best way is take really high-speed video, hundreds of
| frames per second, then pick out the frames which has the
| least amount of atmospheric distortion and stack those.
|
| So not only can you compensate for unwanted motion of the
| camera rig, but also for external factors like the
| atmosphere.
|
| For faint deep-sky objects, IIRC you really do want long
| exposures, to overcome sensor noise. At least the
| comparisons I've seen using same total integration time,
| a few long exposures had much more detail and color
| compared to lots of short exposures.
|
| That said, lots of short exposures might be all you can
| do if you're limited by equipment or such, and is
| certainly way better than nothing.
| jfarlow wrote:
| 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
| adolph wrote:
| Are the 100s of nanometers of light larger than the
| perturbations of Brownian motion?
|
| This oldish link would indicate inclusions of lead in
| aluminum at 330degC will move within 2nm in 1/3s but may
| displace by 100s of nanometers over time:
|
| https://www2.lbl.gov/Science-Articles/Archive/MSD-
| Brownian-m...
| Daub wrote:
| 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.
| hammock wrote:
| >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 wrote:
| 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 wrote:
| 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 wrote:
| 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
| cenamus wrote:
| Damn, somehow missed this video as a long time subscriber.
| globnomulous wrote:
| 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 wrote:
| 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 wrote:
| Presumably this could be used for color imaging by using lasers
| of different wavelengths?
| jdiff wrote:
| 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 wrote:
| 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.
| jofer wrote:
| Regular cameras respond to a wide range of wavelenghts, and
| they do actually reasonably mimic the response of the human
| eye.
|
| Either way, it's the "range" vs "single wavelength" that's
| key here. The green band (or blue band or red band) isn't
| one wavelength. It's an average over a fairly broad range.
| Single-wavelength (or very narrow range) images are quite
| different.
| pfdietz wrote:
| A fun example of these effects is "black fire".
|
| https://www.youtube.com/watch?v=F0LWtieip9E
| kulahan wrote:
| 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 wrote:
| i think the applications to spy-craft could be quite interesting
| here. Something for the next mission impossible movie maybe?
| aerostable_slug wrote:
| It's also interesting to consider that they may be reinventing
| prior classified research.
| greggsy wrote:
| 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 wrote:
| How does this compare to the state of the art?
| hammock wrote:
| 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 wrote:
| LIDAR pulses are in the order of a few nanoseconds.
| hammock wrote:
| How many pulses per second?
| therein wrote:
| Matter-wave lasers coming soon.
| krige wrote:
| wave motion lasers just right after!
| codeulike wrote:
| ... but only if its written on shiny paper
| mrexroad wrote:
| > 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 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| Except when it's raining
| alexalx666 wrote:
| the website delights with the absence of ads throwing up into my
| eyes
| grues-dinner wrote:
| Use Firefox and Unlock Origin and that can be every website,
| even on mobile.
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