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As an honest citizen, I do not intend to violate the laws of thermodynamics by concentrating the light emitted by a blackbody on a smaller area. However by playing with this wonderful 2d ray online simulator and inserting this json I get this result:

enter image description here enter image description here

You can see that I have tried to simulate the diffuse emission of a spherical blackbody with these 180 degrees point sources placed around a spherical light absorber. I have placed two ideal lenses of very high concentration (I guess you could manufacture these lenses as fresnel lenses, or maybe not and that's the point), and as you can see I now have a colimated beam of higher light concentration inside my lightpipes, with which I would be able to heat a target to higher temperature than the blackbody.

I do not think I violate the law of conservation of etendue as etendue is conserved in my system. I have read as well these posts about this subject, but I couldn't figure out why their answer would rule out this contraption.

So my question is: Why is this not possible? What is the issue with my simulation?

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  • $\begingroup$ Actually, it seems POSSIBLE. In this paper it is shown that using nonimaging optics sunlight can be concentrated higher than its concentration at the surface of the sun (!) link to paper $\endgroup$
    – Alexis Gros
    Commented Jan 31, 2023 at 22:13
  • $\begingroup$ It looks to me like your simulated lenses violate the conservation of etendue. A lens that deflects the central angle that extremely must also expand the solid angle extremely. Your ray tracing appears to show that lens both deflecting and concentrating, which is not possible. However, it is difficult to be sure from the diagram so I will not post an answer to that effect. $\endgroup$
    – Dale
    Commented Feb 1, 2023 at 16:53
  • $\begingroup$ Thanks for the answer, I have added a close up of one lens in my original message to help you see the rays better. You can also use the links in my answer to play with the optical simulation youself. $\endgroup$
    – Alexis Gros
    Commented Feb 2, 2023 at 7:23
  • $\begingroup$ Yes, with the close up it seems clear that the lens is impossible. $\endgroup$
    – Dale
    Commented Feb 2, 2023 at 11:44

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