"Henri Wilson" HW@.... wrote in message
...
On Fri, 4 May 2007 14:16:37 +0100, "George Dishman"

wrote:


"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

Yes I'm familiar with that kind of result. De Broglie waves are quite
amazing
really. It shows that matter and 'fields' are not very far apart in
nature.

George, there is nothing here that surprises me. Single photons making up
a
monochromatic beam should have the same wavelength as the beam itself. The
beam
is just 'lots of them'.

Finally, you have cottoned on to what I have been
saying. In the experiment they used a current of
10 electrons per second. Obviously the diffraction
pattern is not what you would predict using a frequency
of 10Hz in your "grating equation". Each electron
behaves entirely independently of the others and
the pattern that builds up is controlled by the
intrinsic properties of an electron. If you use
the interference pattern via Huygens to work out a
wavelength, it is the wavelength of an electron that
you get, not the 29979245.8m wavelength that
corresponds to a frequency of 10Hz.

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.


that's good.

Incidentally, did you notice at the top it says

"This detector was specially modified for
electrons from the photon detector produced
by Hamamatsu Photonics (PIAS)."

It is just a photomultiplier with the front end
photoelectric element removed.

George