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The field of nonlinear optics deals with photon-photon interactions in matter, and has been around for almost a century. https://en.wikipedia.org/wiki/Nonlinea

• westurner 2y ago
  Do they model photons as rays, vectors, particles, waves, or fluids? https://en.wikipedia.org/wiki/Nonlinear_optics https://en.wikipedia.org/wiki/Nonlinear_optics : > In nonlinear optics, the superposition principle no longer holds.[1][2][3] But phonons are quantum waves in or through matter and the superposition principle holds with phonons AFAIU
  • gus_massa 2y ago
    Superposition is valid in vacuum, well, actually, until the photons have enough energy to colide and form an electron-positron pair. It's also valid in most transparent material, again, assuming 1) each photon has no enough energy for example to extract an electron form the material like in the photoelectric effect, or creating an electron and a hole in a semiconductor, or ... 2) there are not enough photons, so you can model the effect using linear equations And there are weird materials where the non linear effects are easy to trigger. The conclusion is that superposition is only a nice approximation in the easy case.