Re: polarized lasers?

[Mark Sylvester <msylvest@spin.it>]

1. Are you sure it's rotating? My observations are that it flips back and
forth between perpendicular states.

2. I've heard various accounts as to the mechanism that produces the
polarization. It seems to depend on the kind of tube, and is not entirely
clear to me. People talk about a small asymmetry favouring one mode which
then dominates. Some tubes have brewster mirrors on the ends, but for these
the polarization is fixed.

3. The flipping back and forth is clearly related to the thermal expansion
of the tube. The period gets longer as thermal equilibrium is reached. I've
been told that successive resonant modes are excited as the tube expands.

4. For this one I've heard nothing remotely like a satisfactory explanation
from any source: why do the successive modes turn out to have opposite
polarization? I've been after the answer to this for years now.


Kyle Forinash wrote:

> I was showing a polarizer filter in class today and a student asked if
> laser light was or could be polarized. I didn't know and tested it out on a
> NeHe laser and one of those solid state ponter pen lasers. Both showed some
> polarization.
>
> Interestingly the NeHe laser polarization ROTATES with about a 9s period
> (holding the filter still the intensity of the transmitted beam varied over
> time). Can anyone give me an explanation of what is going on, why polarized
> and why rotating?
>
> kyle
*************************************************************
Mark Sylvester
United World College of the Adriatic, Duino, Trieste, Italy.
msylvest@spin.it
tel: +39 40 3739 255
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