Laser technique measures distances with nanometre precision | Hacker News Reader

Laser technique measures distances with nanometre precision

newscientist.com

39 pointswesturner20 comments

> 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

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.

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.

From https://news.ycombinator.com/item?id=42330179 .. https://www.notebookcheck.net/University-of-Tokyo-researcher... :

> multispectral [UV + IR] camera ... optical, non-contact method to detect [blood pressure, hypertension, blood glucose levels, and diabetes]." [ for "Non-Contact Biometric System for Early Detection of Hypertension and Diabetes" https://www.ahajournals.org/doi/10.1161/circ.150.suppl_1.413... ]

>> "Tongue Disease Prediction Based on Machine Learning Algorithms" (2024) https://www.mdpi.com/2227-7080/12/7/97 :

>>> new imaging system to analyze and extract tongue color features at different color saturations and under different light conditions from five color space models (RGB, YcbCr, HSV, LAB, and YIQ). [ and XGboost ]

"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?

Oooh it's the guy with octal years!

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.

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

See The Long Now Foundation.

Why not two zeros? Or three, or more?

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.

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

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.

Aha! Yes, very much harder.

I skipped the article, went directly to the paper https://arxiv.org/abs/2412.05542

It is very readable. This measures absolute distance.

LIGO was its own thing https://en.wikipedia.org/wiki/LIGO many people, big vacuum.

Two sites, one by Hanford the other in a swamp https://www.ligo.caltech.edu/WA https://www.ligo.caltech.edu/LA

Thank you! I'll check it out.

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.

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.

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!

It will not, or even for less-than-car-sized optical manufacturing.

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