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So, I have an idea that's also sort of questions I can't find the answers to.
I want to focus rays from the sun either using a large parabolic dish covered in mirror shards, or ideally through a large Fresnel lens and then direct those rays down the length of a circular tube with a mirrored interior
surface to create a portable solar cutting torch/kiln furnace.
Given a perfect lens, a perfectly circular tube and 100% reflection:
Will the rays pass through one another down the length of the tube and refocus at a distant point?
...and if so, would the same hold true for a bent tube? Could focussed light be redirected to distant points, say even underground?
...and why is there absolutely no information to be found on the reflectiveness of natural obsidian?
https://www.youtube...watch?v=Sh8EEDuiQ54
[pashute, Nov 01 2015]
[link]
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Could you use a fiber optic instead? |
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Why not use total internal reflection? |
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Same principal I guess eh? but would the light rays re-converge after bending around corners? I try to visualize it, but it hurts. |
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//Will the rays pass through one another down the
length of the tube and refocus at a distant
point?// |
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You'll need a lens at some point. Think about the
point at which the parabolic dish (or Fresnel lens)
focusses the rays. They are arriving from all of the
dish/lens, and hence at all different angles.
They'll therefore bounce down the light-pipe at all
different angles. |
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For instance, a ray that comes from the centre of
the dish will travel straight to the focal point, and
straight down the middle of the light pipe (if it's
straight). A ray that comes from the edge of the
dish will enter the pipe at an angle, and will
bounce back and forth along the pipe. |
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So, when the rays exit the pipe, they're going to be
heading in all different directions. |
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And, as I recall from an earlier discussion here, you
can't focus light down to a point smaller than the
source - in this case the disc of the sun as viewed
from Earth. |
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hm... I don't want to tighten the focus at all. Because the rays are at an angle to converge when they enter the tube, in my mind I saw them passing through one another at re-convergent intervals down the length of the tube. I get what you're saying though, the straight-line photon will get to the distant focal point slightly faster than the mid-mirror photon, which would arrive faster than the outermost... etc. |
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Cool.
How about a variation of a Fresnel lens or reflector which, instead of bending concentric rings of light to a focal point, was designed to take the length and curvature of the conduit into account and scatter light accordingly. Could the topology of the lens/reflector needed to do this be figured out by algorithm?
and perhaps even morphed to adapt as needed? |
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You can't focus light smaller than the source? I
thought it was you can't make it hotter than the
source... what if you collimate it first? |
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