Scientists discover laser light can cast a shadow | Hacker News Reader

Scientists discover laser light can cast a shadow

phys.org

53 pointspasswordoops21 comments

This feels like lazy reporting. One beam isn't blocking the other, it's inducing a localized nonlinear process in a material which then absorbs the crossing beam. This isn't a novel process.

It's like me saying if I close a door I'm casting a shadow, sure, I caused it, but it's not my shadow.

I was about to say the same thing... unless they can do this in vacuum, it's a curiosity, but not something novel.

Intense laser light can cause electron-positron pair production[1], but we're not quite there yet AFAIK.

[1]: https://en.wikipedia.org/wiki/Breit%E2%80%93Wheeler_process

Now do it without moving the door. That's what makes this interesting. It uses the crystal, but it's not changing the crystal.

It's changing the crystal not the structure but the state. Ruby crystal are gained medium for laser https://en.wikipedia.org/wiki/Ruby_laser you can pumped them with light.

I suppose one could say that opening a second path in an interferometer also 'casts a shadow', though by a different mechanism.

This sort of usage does not bother me (at least at what I perceive as this benign level.) Metaphor and simile are part of the expressive power of human language, and both writing and reading would become tedious if we tried to eliminate them.

Source publication (3 points, 3 days ago, 3 comments) https://news.ycombinator.com/item?id=42139019

https://www.optica.org/about/newsroom/news_releases/2024/nov...

Paper: https://opg.optica.org/optica/fulltext.cfm?uri=optica-11-11-...

Exploits nonlinear optical interactions in a medium (ruby) to cause one beam to cast a shadow from another beam.

Right. Materials with nonlinear optical properties make optical logic possible. Here's an overview of that.[1]

Cross-gain modulation (XGM)

XGM has been investigated extensively to design optical logic gates with SOA. It is assumed that there are two input light beams for each SOA. One is the probe light and the other is the much stronger pump light. The probe light cannot pass through the SOA when the pump light saturates it. The probe light can go through the SOA when the pump light is absent.

[1] https://www.oejournal.org/article/doi/10.29026/oes.2022.2200...

Additional evidence of photons interacting despite common belief, though:

"Quantum vortices of strongly interacting photons" (2024) https://www.science.org/doi/10.1126/science.adh5315

Photons affect mass by causing phonons, which affects scattering and re-emission; so thereby photons interact with photons through light-matter photon-phonon interactions.

From the article:

> Absorption of the green laser heats the cube, which changes the phonon population and lattice spacing and, in turn, the opacity.

/? are photons really massless: https://www.google.com/search?q=are+photons+really+massless

Y: because otherwise E=mc^2 is wrong

N: because it's never been proven that photons are massless

N: because photons are affected by black holes' massful gravitational attraction, and/or magnetic fields

N: because "solar wind" and "radiation pressure" cause displacement

If photons are slightly massful, then coherent light photons would draw together over long distances; thus they interact.

"Light and gravitational waves don't arrive simultaneously" https://news.ycombinator.com/item?id=38061551

"Physicists discover that gravity can create light" https://phys.org/news/2023-04-physicists-gravity.html https://news.ycombinator.com/item?id=35633291

Link to the paper in Optica, "Shadow of a laser beam"

https://opg.optica.org/optica/fulltext.cfm?uri=optica-11-11-...

Maybe this is wishful thinking but could something like this be used to make star wars style holograms? Strategically placed laser shadows to block light sounds like a useful tool in that direction.

We have holograms that are in 'open' space. The problem is they aren't particularly fast, safe, or interestingly- quiet.

The ones I know of converge multiple beams at a point; this results in a Bloom (https://en.m.wikipedia.org/wiki/Thermal_blooming). Not sure how they aim the beams. (Voice coil and mirrors, digital mirror device aka DLP. Both valid options with pros and cons)

So slapdash Unity asset store video games were right all along!

Never bet against Unity

This seems interesting and bit lame quirk but I've a gut feeling there is a lot more potential here

Interesting, Initially I thought it was a laser-laser interaction happening in vacuum.

You can make logical gates from this, right?

Like a floating electrical circuit, or one inside some sort of fiber-optic, performing in a transistor, resistor, or diode like way?

How would you manage the excess/unused/unwanted laser though, switching? I.e. would it be absorbed or reused to prevent it bouncing around etc.

I guess so... probably OOK, I wonder what's the relaxation time of the medium

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