> 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

"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?

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.