Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Novaflipps on 09/11/2016 21:13:25
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If it was possible to make a soundwave that matched a lightwave, say infrared light, would it get amplified?
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You can make sound and infra-red light from a laser pass through the same bit of air at the same time, but they won't interact if the air is perfectly clear.
If the air has some dust in it, the laser light would be scattered from the dust, causing some doppler shift, which could be measured. But the wavelength of sound at 3kHz is 10cm, so the dust would need to be constrained to a very narrow region - say 2cm wide.
If you pass a laser beam through optical fiber, sound striking the fiber will cause it to vibrate, and this will affect the phase of light passing through the fiber. By comparing the light that passed through the fiber vs light direct from the laser, you can detect the sound striking the optical fiber. This method is sometimes used as a hydrophone, to detect sounds underwater.
I can see how sound would modulate a light beam, but I don't see how a laser could amplify sound.
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If you could use the technology used in noise cancelling headphones, and time a powerful laser directed into a Parabola you could create shockwaves from the superheated air and you may be able to amplify the soundwaves that way.
Although A. that is just the first thing that popped into my head so it probably wouldn't actually work, and would required way too much energy to be feasible, and B. you aren't actually using infrared wavelengths to interact with the soundwaves directly so i guess it doesn't really answer the question you asked.
EDIT* I noticed that the question was whether a soundwave could amplify a lightwave so i did answer a different question entirely.
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I am not answering so much as asking another question but if the soundwaves were in a different medium such as water would it be possible to use soundwaves to focus the light? say they were powerful enough is there any way the pressure differential could create some sort of a lens?
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... if the soundwaves were in a different medium such as water would it be possible to use soundwaves to focus the light? say they were powerful enough is there any way the pressure differential could create some sort of a lens?
Are you thinking that the soundwaves could be focussed in someway that changed the density of the water in a local area? You would need to work out the density gradient you would need and what sound power would be needed to do it.
Interesting idea.
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Hmm. Btw thanks for the answers. But how high frequenzy can sound have, and could it be possible to get sound wave and light wave to ''phase'' in some form? And would it be possible to measure it in some way? Edit: Execpt in a fiber optic cable:)
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Visible light has an incredibly high frequency compared to audible sounds. Most people probably hear up to about 20 kHz. In Contrast, blue light has a frequency in the range of 700000000000 kHz. There are forms of electromagnetic radiation with frequencies as low as 20kHz, but these are incredibly low energy, with very long wavelengths (like 10 km).
Also, light waves and sounds waves are very different. Light is electromagnetic waves, while sound is pressure waves. These will not add to each other the way they can combine with themselves (light interacts with light in a similar way to how sound interacts with sound, but light and sound cannot interact in the same way).
However, one could imagine that if the wavelengths of sound and light were similar, that there could be some interesting effect. The refractive index of air depends on the pressure of the air, and sounds involve changing the pressure of the air. One could imagine a very high amplitude sound wave of the right wavelength could cause some degree of diffraction of light with the right frequency. This certainly wouldn't work for visible light, but perhaps with microwaves?
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... light waves and sounds waves are very different. Light is electromagnetic waves, while sound is pressure waves. These will not add to each other the way they can combine with themselves (light interacts with light in a similar way to how sound interacts with sound, but light and sound cannot interact in the same way).
Sound can generate light ... https://wikipedia.org/wiki/Sonoluminescence