On Jun 1, 1:52*pm, Cecil Moore wrote:
On Jun 1, 8:10*am, K1TTT wrote:

what exactly is the 'interaction' *and why is it unique to that
special coherent, collimated, etc, case?

Is it not obvious that when two reflected waves cancel in one
direction, as at the surface of a 1/4WL thin-film coating on glass,
and their combined EM energy is redistributed in the opposite
direction, that those two waves have interacted, i.e. have suffered a
permanent change and have lost their original identities?

Is it not obvious that when two waves are traveling two different
paths where the incident angle is, e.g. two degrees, that those two
waves will superpose and interfere throughout a certain space after
which they emerge intact, unaffected, and have obviously not
interacted, i.e. they suffered no permanent change and have maintained
their original identities?

no, it is not obvious. where do you draw the line... 1 degree, .1
degree, .001 degree? at what point is the angle small enough to say
that they have 'interacted' and the energy is redistributed?


Did superposition occur in both cases? Yes. Did interference occur in
both cases? Yes. Did wave cancellation occur in both cases? No, just
in the non-reflective glass case.


i propose that 'cancellation' is just a special case of interference
where the waves are 'close enough' to collinear that you never see the
interference pattern. this would of course always apply in a
transmission line because they are confined.

closely analyze the transient response of your non-reflective glass in
the case where the wave is not incident perpendicular to the glass.
do each reflection from each interface separately as the wave travels
in the coating at an angle. then reduce the angle to very near
perpendicular and you should see that there are indeed reflections
that should very nearly 'cancel' each other out as the number of
reflections gets bigger.