[westurner]

It is possible to infer phase from second order intensity via the Huygens-Steiner theorem for rigid body rotation, FWIU: https://news.ycombinator.com/item?id=42663342 .. https://news.ycombinator.com/item?id=37226121#37226160

Doesn't that mean that any camera can be used to infer phase (and thus depth for face ID, which is a high risk application)?

> variable focus

A light field camera (with "infinite" focus) would also work.

[MengerSponge]

Very cool. Yes, probably? I'll have to think about the relationship between image quality and the fidelity of the derived phase measurement, because it's not obvious how good a camera needs to be to be "good enough" for a secure system.

Light field? I remember Lytro! Such cool technology that never found its niche. https://en.wikipedia.org/wiki/Lytro

Is anybody making a successor product?

[westurner]

I guess the task is to design an experiment to test the error between phase inferred from intensity in a digital camera by Huygens-Steiner and a barycentric coordinate map And far more expensive photonic phase sensors.

Is (framerate-1 Hz) a limit, due to the discrete derivative being null for the first n points?

Fortunately this article explained the implications of said breakthrough; "Physicists use a 350-year-old theorem [Huygens-Steiner] to reveal new properties of light waves" https://phys.org/news/2023-08-physicists-year-old-theorem-re... :

> This means that hard-to-measure optical properties such as amplitudes, phases and correlations—perhaps even these of quantum wave systems—can be deduced from something a lot easier to measure: light intensity.

IDK what happened with wave field cameras like the Lytro. They're possibly useful for face ID, too?

"SAR wavefield". There's a thing.

From https://news.ycombinator.com/item?id=32819838 :

> Wave Field recordings are probably [would probably be] the most complete known descriptions of the brain and its nonlinear fields?