Date: Tue Oct 13 14:27:43 2009

Author: Zani, Gerald

Subject: Re: 1/4 wave plates

Post:

Dale,

I am not convinced that what you describe is correct, Dale.

What you describe appears is like a 1/4 wave plate is being used as a
circular polarizer. But It ain't.

A 1/4 wave plate needs another polarizer to be transformed into a
circular polarizer.
The combination of a 1/4 wave plate together with a polarizer is what
makes a circular polarizer.

Am I wrong?

Shouldn't it be like this instead:

Place a linear polarizer on the OHP.
Place a combo of a 1/4 wave plate PLUS linear polarizer together onto
the OHP polarizer at 45 degrees wrt the polarizer.
Place another polarizer on top and rotate.

So in fact you have three polarizers and a 1/4 wave plate all together,
not just two polarizers.

Yes? - jz

-----Original Message-----
From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu] On
Behalf Of Dale E. Stille
Sent: Tuesday, October 13, 2009 1:53 PM
To: tap-l@lists.ncsu.edu
Subject: Re: [tap-l] 1/4 wave plates

George,

So, here is how the instructor did it, which I am not convinced is
right.

Place a linear polarizer on the overhead projector. Then place the 1/4
wave plate on the polarizer and at 45 degrees with respect to the
polarizer. Place another polarizer on top of these and rotate it to see

if the intensity changes.

Dale

George Herold wrote:
> Dale, can you describe the optics setup in more detail. What is the
> light source? Where and how many linear polarizer's.
>
> 1/4 wave plates are 'designed' for one wavelength. The cheap plastic
> ones have bit of a spread in their optical thickness... But you can
> 'tune' them by rotating them about one of the optical axes
>
> George H.
>
> -----Original Message-----
> From: tap-l-owner@lists.ncsu.edu [mailto:tap-l-owner@lists.ncsu.edu]
On
> Behalf Of Dale E. Stille
> Sent: Tuesday, October 13, 2009 12:42 PM
> To: tap-l@lists.ncsu.edu
> Subject: Re: [tap-l] 1/4 wave plates
>
> Tappers,
>
> I just brought out the 1/4 wave plate stuff that I have accumulated or
> bought ( specifically from Edmund and Sargent Welch ) over the years
for
> optics class. Apparently none of them are 1/4 wave plates in the fact
> that they do not satisfy the statement:
> "With incident natural light, the two constituent P-states (sorry I
> don't have the proper script for the P ) are incoherent; that is,
their
> relative phase difference changes randomly and rapidly. The
> introduction of an additional constant phase shift by any form of
> retarder will still result in a random phase difference and thus have
no
> noticeable effect."
> In other words, the intensity of the light coming through the 1/4 wave
> plate should remain the same as one of the polarizers is rotated.
> That ain't happening for us except on a very old quartz plate we
found.
> We have even tried some color compensation with filters to see if what
> we had was color dependent. That also didn't work.
>
> Anyone else out there have this experience and if so, what did you
find
> that worked for you??
>
> Dale Stille
> U of Iowa
>
>

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