CDR: Re: Choate physics again

[Jim Choate]

On Thu, 28 Sep 2000, Michael Motyka wrote:

> Wasn't it grounding and Maxwell's equations last time? I can't believe
> I'm falling for this again but here goes...

No, that was Tim's fucked up physics. He was the one claiming Gauss's Law
didn't apply and charge didn't reside on the outside of objects made of
conductors.

> Actually I didn't write this ^

I didn't say you did, I only cut the quote out of somebody elses reply.
If it's mis-appropriated you should bitch at them. I made a clear note
that I had NOT seen the original and was replying to a copy.

Get your facts straight.

> I think what he was trying to convey were the effects of reflection,
> absortion and diffusion.  etc...

Those are mechanisms that lead to the loss of coherence of the photon
emissions from the original source. You're confusing cause and effect.

> I am not an optics expert but I DO have a clue. And any coherence in the
> light that hits the film in my Canon as I snap one poorly composed photo
> after another is purely accidental unless the scene has been painted by
> a targetting system.

Bullshit. If the photons that come off the reflected or secondary source
are distrupted in their phase then no recognizable picture will form.

> What is a laser Jim? LASER
> 
> Light
> Amplification by the 
> Stimulated
> Emission of
> Radiation

Yeah, so where in 'coherence' in there? I know what MASER means too.

> An atom in an excited state, ie one that is not in the ground state, may
> be stimulated to release a photon by an incoming photon. The most
> interesting part of this is that the emitted photon after the
> interaction is in phase with the incoming photon and in the same
> direction.

No, it is NOT in phase with the incoming photon. It IS in phase with the
secondary photons emitted by the material in the lasing body. In general
the optical pump for a laser is a optical flash and it emits no
recognizable coherent photons.

> Get lots of these interactions taking place in the right medium and you get 
> a river of photons all in phase. That's what coherent means in optics - in 
> phase.

Exactly. And if the photons are not coherent with respect to arrival time
and flight path when you try to take a photo then no picture will occur.
Instead you get a blob.

Note that I am NOT saying the photons are coherent with respect to
their individual waveshapes (ie peaks/vallies match) but rather that their
emission and arrival time are coherent, they happen at the same time and
follow rougly parallel paths (now do you get it, I didnt' think so.).

> Go to any optics book. Want references?

No thanks, I've got quite a few right here. Beside that I've spent the
last 30 or so years building this sorta shit.

Study nature, not books.

             Louis Agassiz
 
> Thermal radiation ( what you are imaging with your snooperscope ) is not
> coherent by any definition that I know of. 

Yes, it is time-coherent as well as path-coherent (they must be parallel
in order to make a picture). The wall does two things:

It causes the photons emitted at the same time from the source to be
received at different time, this interupts the ability of the receiver to
correlate (i.e. verify coherence) them into a recognizable picture.

The second thing it does is take the intialy parallel rays of light and
break that parellelism, their coherence with respect to path (in other
words their coherence with respect to geometry, lasers require this as
well to laze, it's more than the emitted photons being in step, they
have to be parallel also). The photons that are re-emitted from an
intermediary barrier are NOT parallel (or coherent) with the original
source photons.

[more pseudo-science deleted]

Coherent in physics means 'in phase' or 'in step', it does not mean 'in
phase only with respect to individual wave equations'. There are LOTS of
forms of coherence in physics that have nothing to do with lasers or even
optics. Coherent means correlated with respect to some characteristic.

Instead of reading about a laser, build a couple.

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