Re: Unpolarized light

["John S. Denker" <jsd@MONMOUTH.COM>]

James McLean wrote:

>  Can a single photon be unpolarized?

No.  That's the point.  As I wrote yesterday, the adjective
"unpolarized" applies only to mixtures, to ensembles of
photons.

> ... (including an arbitrary phase, then averaging at
> the end) works mathematically, I've never been completely <satisfied
> with/confident in> my own *physical* picture of unpolarized light.  How
> can the phase vary without also varying the wavelength?

Huh?  What's phase got to do with wavelength?  The
usual expression is
        phi(x) = sin(k*x + theta)
where k=2pi/wavelength and theta is the phase.  Note that
the phase is not time-dependent or space-dependent for any
particular photon;  we just get a new phase each time we
draw a photon from the ensemble.

> The best I think I've come up with is the superposition of many wave
> packets (photons?), each with a randomly selected but definite
> polarization.

Exactly.

> Each packet has a spread of wavelength, of course, but at
> least they all have the same average wavelength.

The fact that they have a spread in wavelength, or any
particular average wavelength, is irrelevant to the discussion.
The question of whether the light is polychromatic or
nearly-monochromatic is independent of the question of
whether it is highly polarized or highly unpolarized.

Also, a tangential remark: the question of wavelength and/or
spread in wavelength is essentially independent of photon
number, as discussed a couple of months ago.  Wavelength
describes a mode;  photon number describes the occupation
of that mode.