sci.physics.electromag

"amdx" schrieb im Newsbeitrag
news:b584d$47b1c67c$450139ad$31816@KNOLOGY.NET...
> > "amdx" schrieb im Newsbeitrag
> > news:a9252$47b197fe$18d6b40c$23017@KNOLOGY.NET...
> >> Can someone explain how these two relate in a waveguide.
> >> My limited understanding is, group velocity is slow near cutoff and
> >> increases as frequency increases to almost c.
> >> I don't know the difference between group velocity and phase
velocity.
> >> Thanks, Mike
>
> "Josef Matz" wrote in message
> news:47b1adc6$0$379$9b4e6d93@newsspool2.arcor-online.net...
> > Group velocity wants to describe a pulse containing more than one photon
> > frequenccy.
> >
> > In dispersive media the group velocity is a function of frequency of
the
> > photons that form
> > a physical signal. So neighboured frequencies have a little different
> > velocities. That is what is behind.
> >
> > So group velocity as one uses the terminus in hard physical theory is
> > nothing else as the true physical velocity at a certain frequency of the
> > photonic carrier resp. field.
> >
> > Group velocities of wave packets is something apart from that. If you
have
> > a
> > carrier that containes
> > a spectrum of frequencies it describes the broadening of the signal due
to
> > different carrier frequencies in
> > which have different velocities.
> > This definition is therefore unsharp and has only qualitative
picturesque
> > meaning !
> >
> > So group velocity in a sharp sense is just the real velocity which with
> > the
> > field and the photons in move
> > at and only at a certain frequency.
> >
> > Josef Matz
>
> I was in a hurry this morning and didn't ask my main question.
> I think at this point I understand different frequencies travel at
different
> speeds.
> Group Velocity vs Velocity Factor what is the difference?
> If vg = c * sqrt(1 - (f/fc)^2) hmm, maybe I should tell what I think I
know.
> (I'm way over my head on this subject).
> If I generate a spark ( many frequencies) all these frequencies combine
to
> make a waveshape, as the wave travels down the waveguide the waveshape
> changes because different frequencies are traveling at different speeds?
> Correct me as needed.
> So is 'group velocity' the velocity the peak of the signal as it travels
> down the waveguide?
> Forgive my ignorance but the formula vg = c * sqrt(1 - (f/fc)^2) doesn't
> work for me. (1-(f/fc)^2) is negative and I can't get the sqrt of a
> negative. What did I miss?
> Thanks, Mike
>
>
>
>
>

I have seen that at Nimtz too. He modifies the dispersion relation. Since i
have not seen that before
i just can say that light having this dispersion relation does not obey the
wave equation but a more general equation which is called Klein - Gordon
equation. So it is not elliptic polarized light.
Such light can also move in homogene waves but with velocities less than c
and be frozen at f =fc.
For f >fc you get inhomogene waves and those can tunnel almost instant.
Thats proof too.

But whats fc ? I dint know.

So i am going after that, my trial to find out something is that it light
where the ellipse of elliptic polrized light
rotates or in other words the field takes a screw. But ok i am not shure
about that last now.

Josef