Can lasers affect sound waves?

[RLXgno]

Yes, I realize this may not seem like a very smart question but allow me to give some background.

I rent a room from a man in his 60s, let's call him Mr L. Mr L studied Pure Mathematics at university and was busy with his postgrad work when he suffered a schizophrenic breakdown. Because of that he never went into a mathematical career but he still loves maths. For as long as I've known him he has been obsessively working on an idea he had for a noise cancellation device. Basically the idea is that it will use lasers to neutralize the sound waves.

Now I'm not sure if that is at all possible, hence the question - can light waves affect sound waves?

If it can then great and I will cheer Mr L on with his project. However if it cannot work then I need to be able to explain to him exactly why not in no uncertain terms, because for him to obsessively work on something that cannot be is dangerous for his mental health. He is a really sweet man and I would hate for anything to happen to him.

Any advice will be much appreciated

 

[Creator]

I hate noise too;
Buy him a set of noise cancellation headphones...they've been around for years.
http://www.google.com/products/cata...adset&um=1&ie=UTF-8&cid=16764969387755380301#

Working principle:http://en.wikipedia.org/wiki/Active_noise_control
,,,

 

[dacruick]

well I know that sound waves are basically pressure waves in the air. So technically sound waves condense the air. If you change the density will you also change the index of refraction. By changing the index of refraction, you can theoretically measure that index using a laser. And with that index you might be able to find the frequency and amplitude of the noise that caused it.

But to be honest, I don't think that this is a viable technology. I'm no expert, but it seems like there would have to be too much technology for it to be economically efficient.

EDIT: He might need a temperature and humidity sensor, because both of those will effect the refraction of light...I really don't see this working.

 

[Creator]

Basically the idea is that it will use lasers to neutralize the sound waves.

He may be referring to using lasers to initiate or stimulate sound waves coherently; however, this requires designing specialized materials as an intervening medium.
There is some interesting work going on here to develop 'laser' sound emissions.

http://physicsworld.com/cws/article/news/41857

Creator

 

[RLXgno]

I think I need to clarify further. He doesn't intend for the lasers to do something to the air temperature or anything like that.

(Here is the part where I wish I had more of a science education so just bear with me on the paragraph that follows...)
If I remember my Highschool physics correctly, when you take one sound wave and then take another that is exactly the same but with the peaks and valleys opposite of the first wave then the two waves will cancel each other out. This is basically what he intends only he wants a light wave to cancel out the sound wave. He needs it to be a light wave because it moves so much faster so therefore it can "catch up" with and eliminate the sound.

Hence my original question - will a light wave interfere with a sound wave at all? It just doesn't seem that likely to me...

 

[RLXgno]

OK, read the wiki article on Active noise control. That is exactly what he wants to do except he wants to use a laser (light wave) instead of a second sound wave to neutralize the first sound wave. Can THAT be done?

Anyone?

 

[dacruick]

I think I need to clarify further. He doesn't intend for the lasers to do something to the air temperature or anything like that.

(Here is the part where I wish I had more of a science education so just bear with me on the paragraph that follows...)
If I remember my Highschool physics correctly, when you take one sound wave and then take another that is exactly the same but with the peaks and valleys opposite of the first wave then the two waves will cancel each other out. This is basically what he intends only he wants a light wave to cancel out the sound wave. He needs it to be a light wave because it moves so much faster so therefore it can "catch up" with and eliminate the sound.

Hence my original question - will a light wave interfere with a sound wave at all? It just doesn't seem that likely to me...

sound waves are basically pressure waves moving through the air. So in short, no, that will not work.

 

[Dr Lots-o'watts]

For complete destructive interference to take place, you need:

- same frequency (but sound and light differ by MHz)

- same direction (but lasers are directional, while sound is generally spherical)

- same amplitude (but laser amplitude is a measure of electric field, whereas sound amplitude is a measure of air molecule displacement - apples and oranges)

 

[RLXgno]

Thanks for the input! That is more or less what I suspected.

 

[jonthebaptist]

This idea requires the conversion from optical energy to mechanical energy, though I'm not sure why he would want to go to the trouble of creating that type of transducer when there is plenty of available technology converting Electro-magnetic energy into mechanical vibrations, ie. speakers and microphones. However, there is research in a field that goes the opposite way, from sound/mechanical energy to optical energy, Sonoluminescence. That may be of interest.