Could you "trap" light in a medium by perfectly refracting it in multiple media configured in a circle shape?
I don't know if it's even possible but if it was then what would we be able to see?
Posted May 4, 2013, 1:57 PM UTC
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What you're talking about is an optical ring resonator which is a type of optical cavity.
You can trap the light in a ring, but there a few limitations.
The ring has to be coupled to the environment in order to get light in. If there's a way for light to get in there must be a way for light to get out.
We can't make anything perfect, small imperfections will eventually absorb the light or scatter it away.
tl;dr Ring cavities already exist and you can use them to trap light, but the light won't stay there forever.
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How big are these instruments? Are they massive or super tiny?
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I don't know much about them, but they are typically made out of fiber optics so I would guess they can be millimeters or smaller in diameter.
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There are extremely tiny semiconductor ring cavities, and there are very long fiber optic ring cavities. They are useful in a number of applications; for instance, ring lasers can be used as gyroscopes.
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These are what I was talking about in my post, thanks for the links!
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The question then becomes, how long will light stay in these rings before escape due to imperfections lets it all out? Given the speed of light, it could be a fraction of a second and still be an appreciable amount of time to stay trapped.
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The amount of time energy will stay in a cavity (or any resonator) is proportional to the Q-factor. The Q-factor is approximately the number of oscillations it takes for the system's energy to decrease by a factor of 1/e^2pi.
Optical cavities with Q-factors on the order of hundreds of thousands are possible which would correspond to an exponential decay rate on the order of nanoseconds.
If you took the best optical cavity, coupled a laser to it and then suddenly turned the laser off, light would continue to come out of the cavity for a few nanoseconds.
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Actually, yes it is possible. I can't find any material on it but some teams have assembled circular resonating cavities designed to act as photon storage devices. Not much would be visible though, otherwise light would be escaping the cavity at an appreciable rate.
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Then, the next question comes. Can we make prism towers-like guns with it?
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It's definitely possible, but having it hop from one tower to another in order to change direction is terribly inefficient and would require a LOT more energy to have them same effect
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A black hole does this in the photon sphere
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One scientist actually found a way to basically "trap" light:
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This sounds like total internal reflection, the principle behind fiber optics
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Optical fibres use reflection instead of refraction.
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Total internal reflection is actually a mix of both. What's happening is the refraction angle as determined by Snell's law cannot be satisfied at an angle beyond the interface of the two media.
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My area of expertise is nano-photonics. In practice, you could never build a device that would do this because no material is 100% reflective. Even the best materials still absorb some light.
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There's a professor at UConn that is doing essentially that; he believes that it might be used to send particles back in time.
Edit: link http://www.phys.uconn.edu/~mallett/main/time_travel.htm
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Any such trap can be (and probably is) used to build lasers. Just add an amplifying medium in the lightpath.
E.g. four mirrors at 45deg in a square? Ring laser.
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Optical resonators can be useful, but in some ways they're only half of a device.
If you can include an amplifier in them, you can build a laser. People have built lasers as rings of optical fiber; the fiber itself can be doped with ions that amplify light when some "pump" light is shining on them and adding energy to the system.
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If you really did trap it, you would not see anything since seeing it means some got away.
Just to clarify for some, in order to see the light, some of it must be absorbed by the receptors in your eye. This light is now gone from your trap.
So would the light be in there but not visible?
Yes
What if we opened it in a dark room?
I can't tell exactly what you're asking, but the light that was absorbed by your eye is no longer in the box. Maybe there would be invisible radio waves passing through, but I feel like that's not what you were asking.
What I meant was that the light rays would be in the medium by continual refraction, no light will enter your eye therefore you cannot see the light inside the medium
What about if we were using a one-way mirror?
True one-way mirrors do not exist.
So where ever the light is trapped would be lack.