Re: Is photon a wave packet ?

[Roger Haar <haar@PHYSICS.ARIZONA.EDU>]

Hi,
        Doppler broadening often (usually) is much larger
than the natural line width.  But the light
associated with a transition from single isolated
excited atom is not truly monochromatic.  It has a
natural line width or energy spread. The energy of
the upper state of a transition has a certain
amount of uncertainty in it otherwise the state
would have an infinite lifetime and there would be
no transition.  This is NOT a statistical thing,
individual discrete photons just do not have an
exact energy until their energy is measured.

Thanks
Roger Haar

********************************************************************

William Beaty wrote:
> On Wed, 15 May 2002, Roger Haar wrote:
>
> >         One can experimentally measure the length of a single photon.
>
> Isn't this a measurement of the length of a coherent wavetrain?
>
> I thought that this coherence-length was caused by collisions in the gas
> molecules which emit the light...  as opposed to photons themselves having
> a length.
>
> If a molecule is being knocked about, then obviously can only emit an EM
> wavetrain having a certain number of cycles (a certain length) before it's
> output is suddenly Doppler-shifted during a collision.
>
> Is my understanding screwy?
>
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