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back to article US scientists build laser-killing device

Yale boffins have built a laser light cancelling device roughly analogous to noise-cancelling headphones. Laser (Light Amplification by Stimulated Emission of Radiation) beams are made by pumping electricity or light into a device composed of two opposing mirrors and a so-called gain medium, such as gallium arsenide, between …

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Happy

Did this at home

Laser presentation pointer, put a mirror in the way, no laser behind the mirror, take the mirror away, laser carries on in a straight line.

I know this was done at Yale, but I have always fancied a job at DARPA, when can I start?

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Think I'm missing something

So the device absorbs a laser beam by using another laser to convert it to heat?

Pretty sure I could absorb a laser beam and convert it to heat using say, a house brick?

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The missing something:

They can selective cancel out a small range of wavelengths, effectively not changing other wavelengths.

At least, that was the explanation I read elsewhere.

The applications they've considered are for light transistors, where they can use block a signal using another signal.

Talking about taking up to the visible light spectrum, isn't that just a filter? I think they've been around for a while...

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Pint

@Ian

Ah, that makes more sense now - and sounds much more useful.

Thanks for that.

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Will not work in any useful sense ...

... because you need to know everything about the incoming beam before it gets to you; so either you have to have a conspiracy or have to violate causality:

See:

"Active drains and causality",

P. Kinsler, Phys. Rev. A82, 055804 (2010),

or

http://arxiv.org/abs/1008.2088

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Note

that this sort of cancellation idea is easy with sound, because sound is much slower than the electronics used to generate the cancelling signal; the slight lag can be made undetectable.

Light, however, is not slow.

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Anonymous Coward

Re: Note

"Light, however, is not slow."

That used to be true, but these new-fangled low energy bulbs take bloody ages to come on.

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Pint

Apples And Intel^H^H^H^H^Oranges. Sound...

*

...is a pressure gradient, and photons are particles**. And everything in the universe is Photons.

You cannot create photons, you can only capture and release them, generally using electrons, which are themselves clusters of photons.

That said, the opposing laser beam can synchronously excite the electrons of the capture medium to optimize the absorption of incoming photons. The laser beams themselves are not directly interacting.

Classical Photons simply do not interact. When you cross two beams both continue unaffected. Another example is the WI-FI full duplex "invention". The two signals are not interacting, the electrical currents induced in the third antenna are cancelling.

*now i need a beer.

**yes, they move in ways that make them APPEAR to be waves

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Silver badge

If

you cant blind em with science, baffle them with bullshit?

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Anonymous Coward

Yes, but...

...can we attach this laser-killing device to the head of a seal?

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Silver badge

Interesting

So if a spy were being submerged in a tank full of El Greg's finest, all he would need to do is position his silicon implanted damsel in distress for all the cranial laser protection he needs.

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light... particle and wave..

University physics was a long time ago for me, and there has been a lot of illicitness between then and now..

but, that aside, if my addled memory functions as it should, the theory about light is that it is both wave and particle.

so this cancels the wave, but what about the particle?

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Wave + particle

Light just appears to behave as either one or the other under different conditions. Since the definitions of waves and particles are mutually excusive, light cannot be either. A particle is defined by being at a single point. A wave is defined by being spread over a large space. Human understanding of the fundamental nature of light (and other EM radiation) is limited by our inability to imagine and model the microscopic other than in terms of the macroscopic. Hence our need to compromise with the idea of 'wave/particle duality', even though it is patently absurd.

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light

is more of a "countable wave", than either or both a wave and/or particle.

Any distribution of light can be broken down into a set of modes (wave-like functions that extend over space), inside of which live a (potentially rather complicated) set of mixtures and/or superpositions of countable excitations.

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Boffin

Mostly Particle

I have always imagined photons to be a particle surrounded by an energy field. This would give you the 'wave' effect under certain conditions while still acting like a particle as the photons travel farther from the source. The energy field would interact with matter as a wave for anything that the photon did not directly impact (halted). This would account for how photons act through a diffraction grating. The edges of the field would cause a change in photon direction when they brushed against the grating.

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Anonymous Coward

Definition of Coherence, in context, needs a little adjustment

Frequency and Phase - not amplitude

The same colour light (frequency) and, the emitted wave is continous would be a more appropriate attempt at this definition in the context of the article.

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Not just that

Can't see the point in publishing an article which makes a hashed attempt at explaining how a laser works to a group of people who probably already know.

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future proofing

The explanation is there in case our understanding of the physics involved changes in the future, so someone referring back in 20 or 50 years time to this journal article can see how they came to this conclusion, rather than be puzzled as to how they got a result that may not fit the new understanding.

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Joke

Hear hear

...but what else did you expect fron Stephen Fry?

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Boffin

Definition of Coherence

I believe that coherent signals have the same polarisation as well (or spin depending on the signal type).

@Tom 260

"The explanation is there in case our understanding of the physics involved changes in the future"

That would be a very good reason for the explination to be correct then, no?

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Silver badge

If that's the purpose, it fails miserably.

As the poster noted, his definition of coherence is frelled. I missed that because I already knew what it meant. In fact, I said to myself, "not exactly, but I suppose it is close enough for someone who is completely clueless and would get lost in the actual definition."

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Boffin

Worse than useless?

Not only is there the heat caused by the absorption of the original beam, but presumably the same energy is required in the cancelling beam - so you have twice as much heat to get rid of as if you hadn't bothered.

Caveat: it's a long time since I looked at lasers (now protect your remaining eye).

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Black Helicopters

Don't tell Sony...

...or they will find a way to recall all PS3s and implant a blu-ray killer that is triggered should it ever detect jailbreak.

Promptly defeated by a blu-ray reader replacement, though. Or an external drive.

Can I coat my windows in that to avoid laser-eavesdropping?

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The ultimate PMR "Black" paint?

So, this converts IR into heat very well?

For low energy targetting lasers it sounds ideal, however a well structured deeper materiel should show the same absorption response for a much wider specturm.

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Well structured deeper material

By 'Well structured deeper material'... you mean... a brick? (see earlier response)

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Thumb Up

If I understand this correctly...

...what they've actually got is a mechanism for bringing two laser beams of the same wavelength and arbitrary phase into a defined phase relationship (in this case 180 degrees out of phase with each other so they cancel out) using a simple passive device.

This actually strikes me as quite a neat trick, and, given the history of the Laser itself (which languished for years filed under "solution looking for a problem" I wouldn't be at all surprised if it turned out to be quite mind bogglingly useful in a "Doh! Why didn't I think of that...!" kind of way for all sorts of things...

--

JG

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Vic
Silver badge

Isn't it obvious?

They've developed this material especially for coating the targets used in the ALTB tests...

There. That should justify a few more $trillion.

Vic.

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Badgers

Title number three. Yarp!

If it works undectectably...will the laser killing device fit on the front of say a car bonnet?

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will it stop the frikkin' sharks

That's the only question.

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Coat

"absorbing 99.999 per cent of incoming light"

They've invented the priest's sock?

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Hmmmmm Me thinking...

IF you could get almost 100% of the energy to convert to a laser light beam, and then direct that to THIS target many (distances) away, and then convert the beam back into electricity.....

Ahem.

I am genius.

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Bronze badge

Great minds, etc.

Yes, I was considering that this might be a fine way to wirelessly transmit power. Race you to the patent office!

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Joke

upsetting

This discover is really going upset the sharks

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Coat

Smoke and mirrors...

... would work to stop lasers just as well...! ;-)

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Can it protect a target

from incoming laser? There are already couple of great ideas here.

If you can cover your car with this stuff (and do it cheaply), it should sell millions in any given day.

If it can protect you from laser weapon, it will be really cool.

Now I want my sharks with laster attached to their heads, while I wear this protective gears.

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