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> Surely light without pauses has way more ability to send two photons one after another than light with pauses.

No it's the opposite, SHG[1] requires huge spatial energy density which also means huge temporal density (power). A continuous wave of the required power would obliterate your retina (and your head).

[1] https://en.wikipedia.org/wiki/Second-harmonic_generation

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It's not discussed in the linked article, but the paper it's based on argues against second harmonic generation and in favor of a two photon absorbtion process [1]. I'm not enough of an expert to comment on the rest of what you said, but I think I agree (based on skimming the paper) that the process still requires a high photon flux (i.e. high power desity).

[1]: https://www.pnas.org/doi/full/10.1073/pnas.1410162111 ; See second paragraph, and/or search the text for "SHG".

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