Light cancellation

[Ian Macmillan]

Dear All,

I apologise in advance for the diagram below, which is intended to show
a monochromatic light source at the left, divided into two beams and
finally recombined by the half silvered mirror at the right to produce
combination beams to the right and downwards.

If the phase and amplitude of the beams is carefully controlled, it should
be
possible to make both combination beams cancel.

If this is possible, would this cancellation
affect the output of the light source?

/-------\
| |
*>---/-------\===>
"
"
A constant width font will display this diagram best.

All the best
Ian Macmillan

[Keith Blow]

Ian Macmillan wrote:
> Dear All,
>
> I apologise in advance for the diagram below, which is intended to show
> a monochromatic light source at the left, divided into two beams and
> finally recombined by the half silvered mirror at the right to produce
> combination beams to the right and downwards.
>
> If the phase and amplitude of the beams is carefully controlled, it should
> be
> possible to make both combination beams cancel.
>
> If this is possible, would this cancellation
> affect the output of the light source?
>
> /-------\
> | |
> *>---/-------\===>
> "
> "
> A constant width font will display this diagram best.
>
> All the best
> Ian Macmillan
>
>
>
No, what you show is an unbalanced Mach-Zehnder interferometer.
Providing the path difference is shorter than the coherence length of
the beam then you will get the interference effects. The light will
split between the two output arms of the output coupler (straight on and
down the page in your diagram) depending on the phase difference between
the two paths. The interference does not cause any back reflected light
to affect the source.

--
Keith Blow

[Oh No]

Thus spake Ian Macmillan <iandmac@tpg.com.au>
>Dear All,
>
> I apologise in advance for the diagram below, which is intended to show
> a monochromatic light source at the left, divided into two beams and
> finally recombined by the half silvered mirror at the right to produce
> combination beams to the right and downwards.
>
> If the phase and amplitude of the beams is carefully controlled, it should
>be
> possible to make both combination beams cancel.
>
> If this is possible, would this cancellation
> affect the output of the light source?
>
> /-------\
> | |
> *>---/-------\===>
> "
> "
>A constant width font will display this diagram best.
>

I am told this is not possible, and would conflict with conservation of
energy. The resolution of the paradox lies in the fact that there is a
phase shift in the reflection by a half silvered mirror.

Regards

--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)

http://www.teleconnection.info/rqg/MainIndex

[Ian Macmillan]

"Oh No" <NotI@charlesfrancis.wanadoo.co.uk> wrote in message
news:PAHxHECnVd8HFw3x@charlesfrancis.wanadoo.co.uk ...
> Thus spake Ian Macmillan <iandmac@tpg.com.au>
> >Dear All,
> >
> > I apologise in advance for the diagram below, which is intended to show
> > a monochromatic light source at the left, divided into two beams and
> > finally recombined by the half silvered mirror at the right to produce
> > combination beams to the right and downwards.
> >
> > If the phase and amplitude of the beams is carefully controlled, it should
> > be possible to make both combination beams cancel.
> >
> > If this is possible, would this cancellation
> > affect the output of the light source?
> >
> > /-------\
> > | |
> > *>---/-------\===>
> > "
> > "
> >A constant width font will display this diagram best.
> >
>
> I am told this is not possible, and would conflict with conservation of
> energy. The resolution of the paradox lies in the fact that there is a
> phase shift in the reflection by a half silvered mirror.
>
> Regards
>
> --
> Charles Francis
> moderator sci.physics.foundations.
> charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
> braces)
>
> http://www.teleconnection.info/rqg/MainIndex
>

At the core of my question was the notion that there are no free photons -
that a photon is not emitted unless it has somewhere in space and time to be
absorbed, so that even a partial cancellation of an emission from a common
source could affect the output, or perhaps the input, of the source.

But I suppose that even if coherence could be maintained, the cancelled
combined beam would still exist as a "ghost" until something in its path
inevitably disturbed its balance and restored it.

Is this reasonable or not?

[Oh No]

Thus spake Ian Macmillan <iandmac@tpg.com.au>
>
>At the core of my question was the notion that there are no free
>photons - that a photon is not emitted unless it has somewhere in space
>and time to be absorbed, so that even a partial cancellation of an
>emission from a common source could affect the output, or perhaps the
>input, of the source.
>
>But I suppose that even if coherence could be maintained, the
>cancelled combined beam would still exist as a "ghost" until something
>in its path inevitably disturbed its balance and restored it.
>
In the case cited, when there is cancellation in one of the recombined
beams, the full beam goes the other way. I think I did hear of an
experiment in which the emission of a photon was suppressed by the fact
that the photon had nowhere to go. Unfortunately I don't recall any
simple description of the experiment, or have any references.

Regards

--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)

http://www.teleconnection.info/rqg/MainIndex