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I imagine it would be very difficult to experimentally determine the energy per photon of monochromatic EM radiation. Since every material reflects/absorbs differently at different wavelengths, I can only see the experimental setup being possible with a black body. Secondly, it is necessary to determine the photon flux (number of photons per time unit).

Have there been any experiments in this direction?

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  • $\begingroup$ Which experimental setup is it that you are thinking of? $\endgroup$
    – The Photon
    Commented Nov 13 at 5:09

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Secondly, it is necessary to determine the photon flux (number of photons per time unit).

Put enough attenuating filters in front of any source and you can reduce its output to the point where you can count the individual photons (given a sensitive enough detector, but this was possible even in the days of detection with chemical films).

Remove the filters to get a strong enough signal to measure the power with a bolometer, knowing that the photon flux is scaled by the attenuation of the filters that were removed.

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  • $\begingroup$ That's obvious. Thank you. What is missing: Have there been any experiments in this direction? $\endgroup$
    – HolgerFiedler
    Commented Nov 13 at 6:16
  • $\begingroup$ Actually a half point, but that doesn't exist. :-) $\endgroup$
    – HolgerFiedler
    Commented Nov 13 at 6:18
  • $\begingroup$ @HolgerFiedler This experiment is so trivial an undergrad instructional lab would be able to do it. I don't know if it's the most accurate way to get the photon energy experimentally, or what practical considerations are needed to get an accurate result. The other thought I had was to find the work function of some metal by some other means and then use a tunable optical source to find the wavelength with corresponding photon energy. $\endgroup$
    – The Photon
    Commented Nov 13 at 7:03
  • $\begingroup$ I‘m interested in the experimental evidence. $\endgroup$
    – HolgerFiedler
    Commented Nov 13 at 9:31
  • $\begingroup$ @HolgerFiedler Why do you suspect that the photons in a monochromatic beam might have different energy than the photons of the same wavelength in blackbody radiation? (In order to understand what kind of experiment you might find convincing) $\endgroup$
    – The Photon
    Commented Nov 13 at 16:35

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