I was thinking about parallel-sided glass blocks, and their
fascinating demonstration of refraction of light on both
entry and exit, and it occurred to me that I've never seen
or heard anything about the beam itself except that it's a
little wider on exit than on entry.

So I wondered: has anyone ever looked at the exit beam in
sufficient detail to detect a spectrum or dismiss the idea?

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On Wednesday, April 15, 2020 at 2:50:01 AM UTC-5, Ned Latham wrote:

I was thinking about parallel-sided glass blocks, and their
fascinating demonstration of refraction of light on both
entry and exit, and it occurred to me that I've never seen
or heard anything about the beam itself except that it's a
little wider on exit than on entry.

So I wondered: has anyone ever looked at the exit beam in
sufficient detail to detect a spectrum or dismiss the idea?

look up Fabry--Perot_interferometer on Wikipedia

Rich L.


[[Mod. note -- There's an e-acute accent on "Perot", but this got garbled
by some non-8-bit-clean software in the posting of this article. :(
The Wikipedia article in question is
https://en.wikipedia.org/wiki/Fabry%E2%80%93P%C3%A9rot_interferometer
-- jt]]

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On 4/15/2020 3:49 AM, Ned Latham wrote:

I was thinking about parallel-sided glass blocks, and their
fascinating demonstration of refraction of light on both
entry and exit, and it occurred to me that I've never seen
or heard anything about the beam itself except that it's a
little wider on exit than on entry.

So I wondered: has anyone ever looked at the exit beam in
sufficient detail to detect a spectrum or dismiss the idea?

Why would you assume exit beam is wider? What if it's focusing down?

Consider a laser beam through the block, When you say looked at in great
detail what do you mean "great"? Generally the progress of say a single
mode laser beam through a material can be theoretically calculated to a
great deal of accuracy. Not saying there might not be some interesting
details found but generally classic theory is usually highly in
agreement with measurements.

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Ned Latham wrote:

I was thinking about parallel-sided glass blocks, and their
fascinating demonstration of refraction of light on both
entry and exit, and it occurred to me that I've never seen
or heard anything about the beam itself except that it's a
little wider on exit than on entry.

So I wondered: has anyone ever looked at the exit beam in
sufficient detail to detect a spectrum or dismiss the idea?

Ten days and no response. I can't find anything relevant on
the web. Is there really no info on this out there?

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On 20/04/17 9:02 PM, benj wrote:

On 4/15/2020 3:49 AM, Ned Latham wrote:

I was thinking about parallel-sided glass blocks, and their
fascinating demonstration of refraction of light on both
entry and exit, and it occurred to me that I've never seen
or heard anything about the beam itself except that it's a
little wider on exit than on entry.

So I wondered: has anyone ever looked at the exit beam in
sufficient detail to detect a spectrum or dismiss the idea?

Why would you assume exit beam is wider? What if it's focusing down?

If it was already a converging beam when entering the glass, it might
still be after exiting (unless it passed its focus point somewhere
inside the block.) So I think that meant here is a parallel beam
entering (but a parallel beam is an idealization, so the question
is not completely clear).

Consider a laser beam through the block,

How the beam is created can be left out of it (but 'monochromatic'
would help to simplify things perhaps, although the shape question
then still stands.)

When you say looked at in great
detail what do you mean "great"?

Exactly, benj. There is a number of increasingly accurate approximations
in physiscs, starting from geometrical optics (simple ray tracing, in
which case a perfect parallel beam is possible and will remain perfect),
then going to geometrical theory of diffraction, physical theory of diffraction, full Maxwell equations, and Quantum Electrodynamics. If
needed even extended with weak and strong-force corrections (or else
the electron has the wrong electromagnetic moment so the propagation
of light will still be described with a slight error)

Generally the progress of say a single
mode laser beam through a material can be theoretically calculated to a
great deal of accuracy.

True, but since the block of material is cosidered large here (I think)
there is no wave guide with discretized 'modes' and a continuum of
possible wave fronts exists.

Not saying there might not be some interesting
details found but generally classic theory is usually highly in
agreement with measurements.

The full Maxwell equations will indeed be the most usefull tool here.
The description is in fact nothing else than light passing through a
window (a widely spread application of parallel-sided blocks of glass.)

--
Jos

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Jos Bergervoet wrote:

benj wrote:

Ned Latham wrote:

I was thinking about parallel-sided glass blocks, and their
fascinating demonstration of refraction of light on both
entry and exit, and it occurred to me that I've never seen
or heard anything about the beam itself except that it's a
little wider on exit than on entry.

So I wondered: has anyone ever looked at the exit beam in
sufficient detail to detect a spectrum or dismiss the idea?

Why would you assume exit beam is wider? What if it's focusing down?

Standard high school stuff. Parallel beam demonstrating refraction.
Nothing more elaborate than that.

----snip----

When you say looked at in great detail what do you mean "great"?

I did not say "great". I said "sufficient".

----snip----

Not saying there might not be some interesting
details found but generally classic theory is usually highly in
agreement with measurements.

I am not questioning theoretical agreement with measurements. I am
asking whether a particular test has ever been conducted.

The full Maxwell equations will indeed be the most usefull tool here.
The description is in fact nothing else than light passing through a
window (a widely spread application of parallel-sided blocks of glass.)

The question is "has anyone ever looked at the exit beam in
sufficient detail to detect a spectrum or dismiss the idea?".


[[Mod. note -- I (the moderator) am (still) unclear as to precisely
what experimental test you are asking about, and I suspect at least
some newsgroup readers may be similarly unclear. I think our discussion
in the newsgroup could be far more interesting & productive if you were
to clarify *precisely* what sort of test you're intererested in.

For example, I don't know whether you're asking about tests involving
(1a) a (nearly-)monochromatic light beam incident on the glass block,
OR
(1b) a broad-spectrum light beam incident on the glass block.

And, I don't know whether you're asking about tests involving
(2a) checking to see if the entire exit beam is or is not monochromatic,
OR (the weaker test)
(2b) checking to see if, at each point across the width of the exit
beam, the light at that point is or is not monochromatic.

If you were to clarify these points, then we could address the question
of whether such a test has already been done & the results published,
and if so, what we might learn from this.
-- jt]]

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