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Re: Faraday isolators



Certainly the "one-wayness" is a similarity, but Carl's point is that it at
least seems that the "one-wayness" of the Faraday isolator can be used to
violate the second law of thermodynamics, by letting an object radiate all
of its internal energy to its (higher temperature) environment. Can the
"one-wayness" of a diode be so (even seemingly) used?

Bob Sciamanda
Physics, Edinboro Univ of PA (ret)
trebor@velocity.net
http://www.velocity.net/~trebor

-----Original Message-----
From: Herbert H Gottlieb <herbgottlieb@JUNO.COM>
To: PHYS-L@LISTS.NAU.EDU <PHYS-L@LISTS.NAU.EDU>
Date: Friday, January 01, 1999 7:27 PM
Subject: Re: Faraday isolators


Don't we have a similar situation with one-way
transmission using diode rectifiers and diode
detectors? There is greater resistance in one
direction than the reverse direction.

Bob Sciamanda <trebor@VELOCITY.NET> writes:
Let me try to get this discussion going:

The Faraday isolator is effectively a pair of crossed polarizers for
the "blocked" radiation.
The (outside) radiation which enters the isolator, but does not exit,
is absorbed inside the isolator and raises the temperature of the
isolator (and the cavity walls of which it is a part). ( As does the
radiation
trapped between any pair of crossed polarizers.)

I think the physics of any polarizing mechanism forbids you, in
principle, from ignoring such absorption (or equivalent energy
re-direction)
effects.

I must add that I didn't fully understand your F/S/F scheme.

-Bob

Bob Sciamanda
Physics, Edinboro Univ of PA (ret)
trebor@velocity.net
http://www.velocity.net/~trebor

-----Original Message-----
From: Carl E. Mungan <cmungan@UWF.EDU>
To: PHYS-L@LISTS.NAU.EDU <PHYS-L@LISTS.NAU.EDU>
Date: Wednesday, December 30, 1998 7:06 PM
Subject: Faraday isolators


It bothers me that Faraday isolators don't obey optical
reversibility. The
fact that looking through one I could see you but you not see me is
disquieting. In particular, I don't quite see how to save Kirchhoff's
law
(absorptivity = emissivity) with these gizmos.

The arrangement I have in mind is simple. A black sample is inserted
into a
cavity having perfectly reflective walls. Then I make a small window
in the
walls into which I place a Faraday isolator. Now what prevents the
sample
from radiating away energy continuously and cooling down to 0 K? The
basic
idea is so simple I'm sure some of you have thought of it before.

To dispense with a couple of objections off the bat:

(1) a Faraday isolator only works at one wavelength - okay, put an
ideal
filter in front of it (i.e., one which perfectly transmits a narrow
passband and perfectly reflects everything else)

(2) a Faraday isolator only transmits one linear polarization - okay,
how
about the following arrangement:
F
S / F

where S is the sample, / is an ideal 45-degree cube polarizing
beamsplitter
which perfectly transmits say the p-polarization and perfectly
reflects the
s-polarization, and F are two isolators consisting of a magnetic
rotator
and an output linear polarizer (which perfectly reflects the
rejected
polarization from the outside and perfectly transmits the other
polarization from both sides) oriented at 45 degrees (to pass the
rotated
light in the usual way). Radiation from the outside which passes
through
either F gets sent out through the open bottom channel of the cube.
Notice
that I have studiously avoided absorption in all components so there
is
nothing to heat up the sample.

Carl Mungan <cmungan@uwf.edu> (who only reads the digest)