Noise cancellation technique can be used to neutralize laser weapons?

[justcurious1]

I had an argument with someone about laser weapons and he/she said "haven’t you listened about noise cancelation technology ? the light is electromagnetic wave as the sound is mechanical wave . The laser rays can be canceled the same way and even using the beam’s own energy ".
there is any scientific base for this statement?.

 

[Vanadium 50]

No.

 

[collinsmark]

Noise cancellation is very wavelength (thus frequency) dependent: The shorter the wavelength (i.e., the higher the frequency), the tougher things gets to cancel. This is due in part to the sensitivity to phase. It becomes much harder to perform a 180 deg phase shift if the wavelength is short and the frequency high.

Noise cancelling headphones are not even concerned with wavelengths less than around 7 mm, since that's beyond the threshold of human hearing. And for practical reasons, the active noise cancellation starts to lose its usefulness at at around 340 mm (1 kHz).

High-powered microwave lasers have wavelengths are in the micrometer range or even smaller. That makes it way, way tougher.

So, theoretically, if you wanted to try anyway, first, you would need some sort of way of adjusting the phase of the active, "noise cancelling" laser. This might be done by adjusting the position of the laser (moving it back and forth), or have some sort of transparent layer of variable thickness. But again, we're talking about the sensitivity in the micrometer or less range.

Another problem is one would have to put the active, "noise cancelling" laser in pretty much exactly the same line of propagation as the original laser (i.e., reducing their relative angles of propagation to be pretty much zero). This isn't practical. So the best you could really hope for is that the two lasers form an interference pattern. So, yes, the original laser might be canceled in some small spatial bands, but its made even worse in other spatial bands.

And for practical reasons alluded to above (with the phase sensitivity, wavelength [frequency] sensitivity, angle sensitivity and all) trying to do laser-based active noise cancellation is probably just worse all around than doing nothing.

 

[Ibix]

there is any scientific base for this statement?.

Light is an electromagnetic wave and you can get wave interference that could redirect and spread the energy.

However, actually using this defensively? No. Setting up interference between light beams is a delicate job in a lab. If one of the beams isn't under your control, and is in fact under the control of people who have an interest in not letting you establish interference effects, then it ain't happening.

Also, your cancellation beam needs the same power as the weapon and needs to be pointing at the target. All the bad guys need to do is shift their aim point (which you can't react to until after the damage is done because lasers travel at lightspeed) and you shoot yourself just as hard as they're shooting you.

There are plausible defenses against laser weapons - reflective layers under your camoflage or ablative armour. Active cancellation is not one of them.

 

[Rive]

Correct me if I'm wrong, please, but (active) noise cancellation is based on an input signal. Which get inverted and released a bit further away, so at the point of cancellation it'll be in (anti)synch with the noise.

In case of electromagnetic waves this implies you get the input signal to the 'point of cancellation' faster than the signal itself (and of course the inevitable delay of circuitry).

Do this with electromagnetic waves - congratulation, at this point you discovered FTL data transmit.
Well, not FTL, actually. With circuit delays and distances making any practical sense, it's rather time travel instead

 

[Ibix]

but (active) noise cancellation is based on an input signal.

There's also the question of how you build a sensor that can take a hit from a laser weapon and still keep working. Might be better to build your tanks out of whatever that sensor's made out of.

 

[russ_watters]

I can imagine how that brainstorming meeting went:
"To protect our personnel against a high energy laser we should shoot them in the face with a high energy laser."
"You're off the team, Bob."

 

[Ivan Seeking]

I had an argument with someone about laser weapons and he/she said "haven’t you listened about noise cancelation technology ? the light is electromagnetic wave as the sound is mechanical wave . The laser rays can be canceled the same way and even using the beam’s own energy ".
there is any scientific base for this statement?.

Diffraction.

 

[collinsmark]

Correct me if I'm wrong, please, but (active) noise cancellation is based on an input signal. Which get inverted and released a bit further away, so at the point of cancellation it'll be in (anti)synch with the noise.

In case of electromagnetic waves this implies you get the input signal to the 'point of cancellation' faster than the signal itself (and of course the inevitable delay of circuitry).

Do this with electromagnetic waves - congratulation, at this point you discovered FTL data transmit.
Well, not FTL, actually. With circuit delays and distances making any practical sense, it's rather time travel instead

That's a good point.

In principle (and only in principle, there are plenty of practical reasons why this won't work) the speed of light limitation wouldn't be such an issue if the attacking laser was a continuous laser, due to a continuous laser's very stable frequency characteristics; very stable frequency is part of what makes a laser a laser.

But the attacker could obfuscate this by using a pulsed laser with random/pseudorandom intervals between pulses. Using active pulsewidths of ~1ns, it means, by my calculations, that the active, "noise cancellation" laser would have to be mere centimeters from the feedback sensor, for it to be at all effective. This essentially requires the rear end of the active, "noise canceling" laser itself to be directly in the bullseye of attacking laser (probably also within mere centimeters of whatever it's trying to protect).

So yeah, I can't imagine anything like this being beneficial at all.