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I was wondering if it was possible, by using only lenses, mirrors, or prisms, to rotate a ray of light coming from a certain direction. For example, if I have two lasers beams side by side, is it possible that after going through an optical setup, that the laser beams appear one on top of each other? I don't want to use stuff like optical fibers or electronics, I just wish to know if it is possible to do it with purely optical devices.

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    $\begingroup$ What would it mean to "rotate a ray of light?" Are you maybe asking about how to rotate an image? There are various ways in which a prism (or system of prisms) can be used to rotate an image by a fixed or variable amount. (e.g., en.wikipedia.org/wiki/Dove_prism en.wikipedia.org/wiki/Porro_prism $\endgroup$ – Solomon Slow Jan 18 '16 at 2:15
  • $\begingroup$ Yes, I suppose I wanted to say "rotate an image". The Dove prism is exactly what I was looking for, thanks. $\endgroup$ – Ermir Jan 18 '16 at 2:28
  • $\begingroup$ @jameslarge Please convert your comment to an answer. $\endgroup$ – rob Jan 18 '16 at 20:35
  • $\begingroup$ What would it mean to "rotate a ray of light?" Are you maybe asking about how to rotate an image? There are various ways in which a prism (or system of prisms) can be used to rotate an image by a fixed or variable amount. (e.g., en.wikipedia.org/wiki/Dove_prism en.wikipedia.org/wiki/Porro_prism $\endgroup$ – Solomon Slow Jan 18 '16 at 20:37
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Yes, it's necessary for example on some telescopes to keep the image the same way up on a camera as the telescope tracks across the sky. VLT naysmyth focus

There are a couple of optical designs, using either rotating prisms or a rotating set of mirrors. Look up field rotator. eg http://www.ing.iac.es/~eng/optics/documents/OPT-WHT-001.pdf

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Yes you can. Moreover, you don't need any lenses and such things, you only need a medium with Refractive index $n(\vec r)$. Using Fermat's principle (https://en.wikipedia.org/wiki/Fermat%27s_principle) you can calculate the path of the light travelling through a medium with $n(\vec r)$. You just have to choose a proper $n(\vec r)$ function.

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