Beat effect with electromagnetic waves?

Question

So everyone knows the beat effect, right? When two hypersonic sound waves interfere a beat is produced whose frequency is equal to the difference between the two waves. If the difference is a frequency in the human hearing range, then we hear a sound from the interference.

My question, which I asked before but did not receive the answer I was looking for, is "does this happen with electromagnetic waves?" If two waves, be it UV, X-ray, or gamma, interfere and have a difference that correlates to a frequency in the visible light spectrum, then would you see a light? I know that being exposed to gamma waves would kill you before you had a chance to appreciate the interference or UV waves would burn your retinas. I don't care. Would there be a visible light emission in any case?

Answer 1

Yes. The intensity of two superimposed laser beams of slightly different optical frequencies will oscillate at a frequency equal to the opitical frequency difference as they go in and out of contructive and destructive interference.

This is most easily accomplished by first splitting the beam with a piezoelectrically driven Bragg Cell. The split-off half of the beam is Doppler shifted by the driver frequency (usually of order 100 MHz). Mirrors and conventional beam splitters are used to bring them back together and overlap them.

Answer 2

EM waves produce "beat" frequencies. Actually, interfering waves produce a sum AND difference frequency frequency. The problem is that to "see" it you must have a very wide-band receiver that can both detect and measure "beat" frequencies. And you must recall that beat freqs fall off in amplitude very rapidly.

An example is your FM radio (if you are that old) - if you listen closely, you will notice that between channels (vernier-tuned, not digitally tuned) you will hear low amplitude squeals and whistles. Some of those are "beat" freqs that got thru the filters in the unit.

ALL EM waves produce beat freqs. There is a rather famous physics experiment where light is passes through two closely spaced slits, and produces a "beat" pattern on the other side.

The problem with "seeing" light from beat freqs of gamma waves is that the amplitude is not enough for you to "see, but it is there.

Ron.

Answer 3

Hypersonic sound works ONLY becasue there is a nonlinear element in the path: air. Air is nonlinear because it can be compressed arbitrarily but cannot be uncompressed below 0 atmospheres.

Beating only occurs when there is a nonlinear element, and this is the only way to get a change in frequencies. Otherwise you have simple summation. The heterodyne principle, in radio, uses highly nonlinear mixers .

f1 + f2 yields products such as f1-2f2 , or f1+f2, only in nonlinear systems. You need a polynomial with order higher than one.

Answer 4

You might be correct but I doubt it and I'll research it some more. This is called the heterodyne effect. However you would need to do it with lasers as ordinary light is not coherent and gamma ray lasers are extremely rare!