"Henri Wilson" HW@.... wrote in message
...

....

A photomultiplier produces a flash for each photon, you should know
that. The basic physics is the photoelectric effect. An electron
ejected
by a photon creates a cascade that generates enough light on the
final phosphor to be measured.

A very sensitive PM might pick up single photons.

All PMs pick up single photons, that's their job!

Their main job is to amplify very weak light signals. A single photon
could
barely be seen above the noise.

This is the experiment done with electrons rather than
photons but if you saw a video of the photon version
it would look exactly the same:

http://www.hqrd.hitachi.co.jp/em/doubleslit.cfm

The site seemed slow and I had to download the movie
rather than view it on-line but it's worth a look so
that you understand the appearance of what we are
discussing. The regions where most photons land are
of course the same as the locations of the fringes
predicted by Huygens' method hence K=1.

George