I'd like to point out two-photon absorption, in which two photons incident on something at the same time are absorbed like a single photon with the total energy

I'd like to point out two-photon absorption, in which two photons incident on something at the same time are absorbed like a single photon with the total energy of both: https://en.wikipedia.org/wiki/Two-photon_absorption https://en.wikipedia.org/wiki/Two-photon_absorption (Too bad that article doesn't mention thermodynamics.) It has wonderful uses like https://en.wikipedia.org/wiki/Two-photon_excitation_microscopy https://en.wikipedia.org/wiki/Two-photon_excitation_microsco...