alt.hn

1/14/2025 at 3:32:27 AM

Laser technique measures distances with nanometre precision

 https://www.newscientist.com/article/2463645-laser-technique-measures-vast-distances-with-nanometre-precision/

by westurner

1/14/2025 at 5:48:36 AM

> optical frequency comb

"113 km absolute ranging with nanometer precision" (2024) https://arxiv.org/abs/2412.05542 :

> two-way dual-comb ranging (TWDCR) approach

> The advanced long-distance ranging technology is expected to have immediate implications for space research initiatives, such as the space telescope array and the satellite gravimetry

by westurner

1/16/2025 at 11:31:27 PM

Note that the precision is very good, however the accuracy is nowhere near as close (fractions of a metre) in the atmosphere, due to the variable refractive index of air. Long term averages can help, of course.

by mikewarot

1/17/2025 at 3:15:40 AM

They talk about this technique for ranging between satellites, which wouldn't have to deal with atmospheric conditions.

For ranging in an atmosphere they suggest dual-comb spectroscopy or two-color methods to account for the atmospheric changes.

by Aurornis

1/16/2025 at 10:34:22 PM

"Vast" really shouldn't have been eliminated from the title, because interferometers have been measuring distances with nanometer precision since even before there were lasers, and lasers have been used in interferometers since the first laser in 01960. Victorian-era interferometers, commonly used for grinding telescope mirrors, could only measure distances of a few meters with precision in the hundreds of nanometers.

However, laser interferometers were already quite good; LIGO, most famously, detected gravitational waves by measuring strains of around 10⁻²⁰ over a distance of 1120 km, which works out to a change in distance of less than 0.000012 nanometers, much less than the width of a proton.

The news here actually seems to be that "A new way to gauge distance using lasers can measure lengths of more than 100 kilometres ... To continue reading, subscribe today with our January sale." So, uh, I don't know, maybe the reporter wasn't familiar with LIGO and thought that nanometer-precision interferometry over kilometers was new? Sitkack, you say there's a paper somewhere?

by kragen

1/16/2025 at 11:13:14 PM

LIGO can accurately measure small (1/2 wavelength) changes in distance, but it does not measure absolute distance.

Absolute is a lot harder to do with interferometers vs. relative measurements.

by opwieurposiu

1/17/2025 at 12:42:19 AM

Aha! Yes, very much harder.

by kragen

1/16/2025 at 10:55:46 PM

Oooh it's the guy with octal years!

by stavros

1/16/2025 at 11:08:21 PM

Noticed that too, but it has a '9' in it.

Best guess is, he's not about to let the Y10K problem catch him napping.

by greenbit

1/16/2025 at 11:31:30 PM

It's kind of silly, but I do like the philosophy behind it: https://longnow.org/ideas/long-now-years-five-digit-dates-an...

by __MatrixMan__

1/17/2025 at 3:17:54 AM

Why not two zeros? Or three, or more?

by dmd

1/17/2025 at 10:37:43 AM

I wholeheartedly support your decision to use three or more zeros on your years in the future.

by kragen

1/17/2025 at 3:56:26 AM

If the people around you are planning for 1y and you're suggesting they plan for 7976y, I think that's probably radical enough.

To suggest they plan for 97975y or 997975y seems a bit obnoxious. At that point you're either just being contentious for the sake of it, or you're pretentiously implying that you have godlike predictive power.

by __MatrixMan__

1/17/2025 at 12:59:15 AM

See The Long Now Foundation.

by cryptonector

1/16/2025 at 10:20:06 PM

I am only two pages in, but I want to say this paper is very well written. People should give reading it a try reading (with LLM assistance).

If this technique could be adapted to existing optical fiber infrastructure, we could see the effects of fiber optic cable stretch and deformation in realtime.

by sitkack

1/16/2025 at 11:17:51 PM

anyone have a sense of whether this will make a difference for small distances as seen in construction and small parts (less than car-sized) non-optical manufacturing? i feel like the precision available today, with handheld laser rules and what-not, are already cheap and accurate enough.

by jiveturkey

1/16/2025 at 11:27:09 PM

Traditional interferometry already achieves sub-nanometer precision. This is already many orders of magnitude more precise than most non-optical manufacturing processes, so I agree with your analysis!

by itishappy