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I'm looking for a impressive, inexpensive lecture demonstration of optical standing wave resonance. Preferably visible light. Can anyone suggest such a demo?

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    $\begingroup$ Do you really mean resonance, or simply interference? The former is really hard - you would need a high Q cavity of some kind (which requires highly reflective surfaces) and a means to interrogate the amplitude inside (which you can't see because it's on the wrong side of a reflector; and if you try to measure it, you disturb the Q). I can't see an "easy" way past that, sorry. Interference, on the other hand, is easier. Can I ask why you would want to use visible light for this? It's easier with (much) longer wavelengths... $\endgroup$ – Floris Nov 14 '14 at 21:53
  • $\begingroup$ How are you going to show resonance without coherence? $\endgroup$ – Carl Witthoft Nov 15 '14 at 1:48
  • $\begingroup$ @Floris - I do mean resonance. Interference is easy. The reason - I'm looking for a visual demonstration of optical resonance - without having to use sensors or instrumentation to sense it. As garyp mentioned the frequency/wavelength is so far away from human visual perception - maybe it's just not possible.. $\endgroup$ – docscience Nov 15 '14 at 3:15
  • $\begingroup$ What do you think it would look like? A laser is of course a great resonator - if you set the end mirrors up "just so" it works but if you spoil the Q of the cavity it extinguishes. So maybe take a HeNe laser apart and slide a microscope cover glass into the cavity - it will stop. Resonance destroyed. Remove glass and resonance happens again. Could that work? $\endgroup$ – Floris Nov 15 '14 at 3:21
  • $\begingroup$ @Floris - yes. Cheap and demonstrative, but tricky getting the cover slip into the cavity without losing the laser gas. Would a strong magnetic field provide enough force to disrupt the resonance? $\endgroup$ – docscience Nov 15 '14 at 22:05
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Before we go too far ... the wavelength of visible light is about half a micron. If you do succeed in setting up standing waves, and figure out how to visualize it, you won't be able to see the wave pattern themselves. The wavelength is too small. You might be able to visualize the increased intensity in the cavity, though. I've seen that in plastic waveguides. It's quite dramatic, and pretty much just what you are looking for. But I don't think a waveguide solution would be quick and inexpensive to set up. One problem with free-space cavities is getting the cavity to be stable. It doesn't take much of a mis-alignment to ruin the resonance. Waveguides take care of that.

You might try a Plexiglas or Lexan rod with polished ends. Or perhaps those multimode fibers that are used in some Christmas trees. A Helium Neon laser. A laser pointer might work. None of these ideas will work the first time. It will take some trial and error.

Maybe someone else has a better idea.

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The simplest is probably a Fabry Perot interferometer and a source of light if well defined wavelength. Years ago we used sodium lamps, but a cheap green laser may be good enough.

This is about as simple as it gets

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  • $\begingroup$ So the interferometer shows fringes - the outcome of interference, but what is observed in the way of resonance? $\endgroup$ – docscience Nov 15 '14 at 22:01
  • $\begingroup$ Such an interferometer is a resonant cavity. Think of the fringes as standing waves. $\endgroup$ – user56903 Nov 15 '14 at 22:53

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