[volemo]

> optically transparent coatings that cycle from 300 to 1K repeatedly and acrylic that has a metal's thermal conductivity

I believe that still wouldn’t work because optical part of the spectrum carries thermal energy too.

[MengerSponge]

Oh hush, you're not going to nerd snipe me into doing the thermal flux calculations today.

Optical photons don't carry an impossible amount of energy: I've seen liquid helium through a small coated window. The window was there for ion beam purposes, not "entertaining the grad student", and it was a big element in the heat budget!