Ah, a bit of clarification needed here. I meant when you get down to one photon, the source should not matter except that the source would determine the wavelength or a range of wavelengths.
From the article, I find this "Here, we demonstrate that single photons deterministically emitted...
laser or flashlight? It shouldn't matter. The question is for one photon. The source should not matter except for a laser, all the photons would be same wavelength and the flashlight would be many.
How about re-framing the question as follows:
If a photon travels down a direction in vacuum, how small a hole will need to be to stop it entirely.
The question might need to be asked first for visible light and then for other wavelengths should there be interesting differences (like the...