Re: A question about the phase difference of the beam splitter.


"Neil Bates" <neil_delver@xxxxxxxxxxxxxxx> wrote in message
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"Adam Norton" <AnortonREMOVETHIS@xxxxxxxxxxxxx> wrote in message
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Take a collimated laser beam and use one beamsplitter to split it into
two beams A and B. Recombine the two beams carefully with a second
beamsplitter to produce two more beams C and D whose intensity depends on
the relative phase of A and B. However if the phase is adjusted so C has
constructive interference and is bright, D will be dark with destructive
interference. This is due to the 180 degree phase change between the
reflected and transmitted light of the beamsplitter. If it were possible
to make a beamsplitter with 0 phase difference, then it would be possible
to either make both C and D disappear or to make their combined energy
greater than the input energy. Anything other than a 180 deg. phase
shift violates conservation of energy.

-Adam Norton


"Sa.Sh." <sasha.ch@xxxxxxxxx> wrote in message
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Adam,

Could yoy please explain your point?

Thank you,

Sasha



"Adam Norton" <AnortonREMOVETHIS@xxxxxxxxxxxxx> wrote in message
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The phase difference is always 180.

If it were 0 deg. then you could make an interferometer where the light
disappears entirely, and of course that can never happen.

--
Adam Norton

Norton Engineered Optics
Optical design and systems engineering for Silicon Valley and beyond.
www.nortonoptics.com

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"Chengxian.Zhang" <zhangchengxian@xxxxxxxxx> wrote in message
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Dear all:
Whether the phase difference between the reflection and transmission
lights of a 50:50 beam splitter is 180 or a modifiable number that
depends on the coating scheme?


Well, I think you could create the "impossible" phase scheme with thin
metallic coatings: Recombine beams into a transparent cube with a diagonal
made of thin metal surface. From symmetry, there can't be a basis for
distinguishing/favoring phase, correct? To avoid violating conservation of
energy, I presume the impedance effects between atoms of metal would just
keep the output the same total energy as went in, but it is interesting to
think about. IOW, sometimes a messy outcome, not being able to use direct
phase reasoning? Another interesting example would be to try frustrated
total internal reflection (same symmetry argument) or microwaves with a
mesh diagonal, etc.

I think, Neil's reply is the closest to what is going on. There are a few
schemes to emplement constructive inteference, still energy seems to be
conserved.
Did anyone measure those interference effects carefully? Any publications?

S.


.

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