Lasers deflected using air | Hacker News Reader

Lasers deflected using air

desy.de

166 pointsgeox29 comments

I'm highly skeptical that this hasn't already been done, considering that acousto-optic lenses are a known thing -- it's just a question of which material you're using (air, crystal, liquid, etc): https://en.wikipedia.org/wiki/Acousto-optic_modulator

Even a 10-second Google search yielded examples of prior art. For example:

https://iopscience.iop.org/article/10.1088/2515-7647/abc23c/...

How is this any different? ¯\_(ツ)_/¯

It might not be clear from the reporting but I guess the paper‘s title (linked from the bottom of the article) might give a clue already:

„Acousto-optic modulation of gigawatt-scale laser pulses in ambient air“, https://www.nature.com/articles/s41566-023-01304-y (open access)

Here’s an excerpt from the abstract:

„Modern photonics […] can involve parameter regimes where the wavelength or high optical powers involved restrict control due to absorption, light-induced damage or optical nonlinearity in solid media. Here we propose to circumvent these constraints using gaseous media tailored by high-intensity ultrasound waves. We demonstrate an implementation of this approach by efficiently deflecting ultrashort laser pulses using ultrasound waves in ambient air, without the use of transmissive solid media. At optical peak powers of 20 GW, exceeding previous limits of solid-based acousto-optic modulation by about three orders of magnitude, we reach a deflection efficiency greater than 50% while preserving excellent beam quality.“

I wondered the same thing. Acousto-optic modulators and deflectors have been commercial items since the late 1970s/early 1980s. I used them in that era. They were even intrinsic parts of laser systems, sitting within the cavity to create pulses of various kinds.

There's also a 50 year history of measuring dynamics in gas and condensed phase systems by the transient grating method which uses laser pulses to generate temporary gratings in all sorts of media. Two short (nanoseconds and on down) cross in a sample (solid, liquid, gas, flame, etc.). They generate an interference pattern and the fringe separation depends on the crossing angle. At points of high intensity, some kind of excitation is created and the refractive index gets modulated by the fringe pattern forming a grating. Now bring in a third pulse at a later time and it will scatter off of this grating. The grating will decay with time as the excitation relaxes due to whatever physical or chemical process is under study. Change the delay between the excitation and probe pulses to get a decay curve which is the observable to be fitted, modeled, compared with theory, etc.

It's different because they are using a gas as an acousto-optic medium. This allowed them to work with laser intensities that are more than three orders of magnitude above the damage threshold of conventional solid-state acousto-optic modulators.

Achieving good diffraction efficiency (they report ~50%) with a gaseous medium is a serious engineering challenge since the refractive index variations due to sound waves are many orders of magnitude weaker than in solids.

I would suggest reading the original publication [1] for more details. It's open access.

[1] https://www.nature.com/articles/s41566-023-01304-y

I really like that this has a little interactive widget. Higher frequencies lead to more splitting/deflection, and higher pressure means more light traveling along the reflected path.

That said, I must also admit that first video's still-image made me assume I was about to see the Master Control Program from Tron.

> In their experiments, the researchers used an infrared laser pulse with a peak power of 20 gigawatts, which corresponds to the power of around two billion LED bulbs.

OK, so not about to revolutionize photonic computers soon. :P

The widget is also done very cleverly. It appears to be a regular HTML <video> element and a slider.

The interactive component in the article was a really nice touch and made it much easier for me to understand the effect at play. I wish we could see more of this in technical articles and scientific publications.

(Off-topic tidbit that I noticed) The interactive widget is actually just a video with a fancy seek bar! If you right-click you can enable the controls and play it like a normal video.

A lot of the video websites really ought to implement the reverse. Easily drag seek without the constant click-wait, click-wait.

Wow, that's a great idea.

It's always amazing how things thought of in science fiction end up becoming reality. In this case bending lasers in air, now we just need a small moon capable of retaining it's atmosphere.

https://en.m.wikipedia.org/wiki/Atmosphere_of_the_Moon

> a small moon capable of retaining it's atmosphere.

That's easy, whatever it retains is its atmosphere. :p

That's no moon...

How is this going to change the hypersonic missile industry? It seems that the only counter measure to hypersonic missile attacks would lie on destroy them with lasers (the only vector that can reliably and accurately go much faster than hypersonic missiles). If someone develops a technology to shield missiles with air, what else could take down such weapons?

The downside of hypersonic missiles is that they are travelling so fast, hitting a stationary object in the air will do significant damage - even raindrops can do damage. So if you detect the incoming hypersonic missile and just fill the sky in front of it with metallic particles, you're good. CSIS calls it "twenty-first century flak".

I guess it's the same difficulty as with reflective coatings - their efficiencies are far from 100%. Even if they manage to repulse most of the energy, some of it still goes through and roasts the missile. Also, this technology only seems to influence a laser beam passing by, not one about to hit head-on.

Very interesting, would this be related to Acousto-optic modulators - https://en.wikipedia.org/wiki/Acousto-optic_modulator, which I believe can do this using a crystal and sound waves.

Will have to read their paper.

Oh nice! I work at DESY (don’t know anything about this though)

https://en.wikipedia.org/wiki/Gradient-index_optics

are we now a step closer to light saber? all we need is a 180 degree deflection

Dang that's cool.

I'd like to know the turning radius.

What do they mean by "efficiency" when they say, "In the first laboratory tests, a strong infrared laser pulse could be redirected in this way with an efficiency of 50 percent?"

I'm assuming this means they deflected 50% of the laser light.

Hmm, that seems problematic -- wouldn't that change it from a laser to a smear?

Maybe? This is absolutely not my field, but I was watching a documentary on the largest visible light telescope that has ever been made and they were talking about the routine they follow when cleaning the primary mirror. The guy running the place said that when the mirror gets dirty, it doesn't degrade the quality of the image, but reduces its brightness (and so sensitivity).

Maybe this is a similar kind of thing?

The article claims that it doesn't hurt the quality of the beam, it just reduces the amount of light

> ... In contrast, we’ve managed to deflect laser beams in a quality-preserving way without contact.

can't wait for styropyro to try this!

edit: for those who don't know --> https://www.youtube.com/@styropyro

Lazy question, it's not possible for parallel lightwaves to interact and deflect orthogonally right.

Point is to try and make a floating image.

cough lightsaber cough

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