On Mar 7, 2:34 pm, Gene Fuller wrote:
Cecil Moore wrote:
K7ITM wrote:
Certainly, those who design and build FTIR spectrometers know
perfectly well that interference does not depend on a narrow-band
coherent source.

How narrow-band? How coherent? In the irradiance (power
density) equation, Ptot = P1 + P2 + 2*sqrt(P1*P2)cos(A),
if the angle 'A' is varying rapidly, what value do you
use for cos(A)?

A constant average sustained level of destructive
interference cannot be maintained between two waves
unless they are coherent. If they are not coherent
the interference will average out to zero.

Gee, I wonder if the experts may have moved beyond the elementary optics
textbook descriptions?

Are you suggesting that FTIR cannot work unless one has your nice 1-D
configurations with perfectly monochromatic waves? Does everything need
to be collinear and coherent?

73,
Gene
W4SZ

So--I have a classic Michelson interferometer, and I see the classic
ring pattern on the screen at the "output" port. I also have a
sensitive microchannel plate detector system that I propose to put in
place of the screen, so that I can reduce the light amplitude to where
it makes sense to be observing it with the very sensitive detector.
In fact, I propose to reduce the light level to the point that the
short wavelength light I'm using is only putting a few photons per
second into the interferometer. I'll count a significant fraction of
those photons and identify where they landed on the microchannel
plate. Do you suppose, Gene, that I'll still see the same
interference pattern that I saw with the much higher intensity light?
Is there any limit to how low a light level I can use and still see
the pattern?

If I do still see the pattern, there must be yet another "dimension" I
need to add to my understanding of the situation -- not rooted in
classical Maxwell e&m.

And of course a dimension that is removed if you think only of average
quantities is time; one who thinks only in terms of averages removes
the possibility of the deeper understanding that resolution as a
function of time allows.

Cheers,
Tom