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?
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.
