Is there a cutoff frequency that makes the underlying mechanism different?I donít think so, but there is a region around visible spectrum where our detection methods start to change so we see more particle behaviour at higher energies than wave behaviour.
Both behaviours are always there, but at lower frequencies it is harder to detect photons as they are down in the noise levels. In radio astronomy photon detection requires cooling of the detectors to reduce thermal noise.
PS you do nice experiments by the way, I like the diffraction/interference ones.
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