Say for example, air and sound can both propagate to air. Now, suppose we have a sound and light wave travelling close by, how would the two waves interact with each other? Suppose I made a very large sound in the path of the ray, would that make any deviation in the motion?
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asked Jan 12, 2021 at 9:00
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1$\begingroup$ Yes, one example being acousto-optic modulators. $\endgroup$– A. P.Jan 12, 2021 at 9:05
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1$\begingroup$ I would say yes but not for being waves. Simply the light would go through a modulated medium. $\endgroup$– AlchimistaJan 12, 2021 at 10:41
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3 Answers
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As mentioned in a comment above, there are also practical uses for interaction between electromagnetic and acoustic waves, particularly in piezoelectric materials. Acousto-optic modulators can shift beams by diffraction, and generate frequency shifts by mixing. These are often used in mode locking and Q-switching lasers.
There are also surface acoustic wave (SAW) devices that are used for oscillators, filters, delay lines and correlators at RF and microwave frequencies.
answered Jan 12, 2021 at 19:29
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Air is made up of particles (atoms, gas molecules). I know that's obvious, but am stating it as a starting point. This means that the index of refraction of air depends on the density (and to a lesser extent on the percentage of each atom/molecule type in the mix).
Now, since the sound wave propogates by causing (or being) a sequence of compressions and rarefications of the atmosphere, there is a resultant pattern of changes in the index of refraction proportional to these pressure differences. The light wave then is deflected according to Snell's Law as the air density changes.
At high optical power densities, the opposite is observable too: heating of the atmosphere caused by the photon interactions leads to pressure waves, i.e. sound.
answered Jan 12, 2021 at 13:10
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1$\begingroup$ the discontinuous change in the index of refraction of air passing a supersonic shock is strong enough to be photographed. The physicists working on the atomic bomb used this effect to follow the progress of the shock wave through the air surrounding a bomb blast. $\endgroup$ Jan 12, 2021 at 18:22
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Carl is right, and if you are flying at max cruise in a newer Boeing airliner and have a window seat on the wing you can actually see the index of refraction "kink" in the air above the wing's skin at about 2/3rds of the way back along the chord, where the air flowing over the wing goes locally supersonic for a bit.
answered Jan 12, 2021 at 18:25