Date: Fri Feb 22 11:52:57 2008 Back to Contents

Author: Urs Lauterburg

Subject: Re: [advlabs-l] Re: Wavelength Dependence of Verdet


I show the Farady-Effect the following way:

I pass the light of a randomly polarized HeNe-laser through a
polarization filter to clearly produce polarized light. The laser
light beam is then adjusted to go through what we call a Faraday
Cell. This a transparent leaded glass cylinder which is surrounded by
a dense coil which can take a few amps. After the beam passed the
cell it goes through another polarization filter which acts as the
analyzer and finally hits a photo detector capable to detect the
brightness of the beam. I then power the Faraday cell coil with
music through a hefty audio amplifier. The cell alters the plain of
polarization according to the music signal. Then if I amplify the
photodetector signal, the music can be picked up again and is made
audible by a speaker. The changing plain of polarization in
combination with the analyzer pol-filter makes the brightness of the
laser beam change in phase with the music. It's an easy way to
modulate a signal onto a distinctly directed beam. Of course
interrupting the beam stops the music because the light is the
carrier of the information.

Maybe you want to set op something like that which is probably easier
to detected than the mere change of the polarization plain.

Regards and have a nice weekend


Urs Lauterburg
Physics demonstrator
Physikalisches Institut
University of Bern

>>Hi Adam,
>>Could you describe a bit your setup, particularly the size of the
>>piece of glass? I've been trying to see Faraday rotation without
>>Kind regards
>>Adolf Cortel
>We are fortunate in that our piece of heavy flint glass (Verdet
>constant of about 0.07 min/G-cm) was "leftover" from some cosmic ray
>experiments. It was used as a scintillation counter, as mentioned
>by Ziggy. It is about 47 x 4.5 x 4.5 cm in dimension. I aim a
>bright laser (green for better visibility) through the long axis of
>the glass. I ensure that the incident light is linearly polarized
>and place a second analyzing linear polarizer at the exitting end.
>One can cross the two polarizers and extinguish the light this way.
>After all of this, I also pass the light through a converging lens
>to project a bigger (yet dimmer, mind you) spot on a screen (with
>all of the lights out). The glass is placed inside the long axis of
>a solenoid coil (~230 turns) that is connected to a beefy power
>supply. When ready, we send a lot of current (~10 amps) through the
>coil and get a magnetic field on the order of 80-160 Gauss where the
>glass is (inside). This magnetic field rotates the axis of the
>polarized light about 5-10 degrees. For show, with the magnetic
>field off, I shine the laser through and see the spot. Then I
>extinguish the light with the second polarizer. Then I turn on the
>magnetic field, and some light reappears on the screen. For values,
>I simply rotate the second polarizer through a measurable angle
>until the light is re-extinguished (magnetic field still on). I
>have even used mirrors to carefully send the laser light back and
>forth through the glass in order to lengthen the amount of time it
>spends in the glass. I was indeed able to get a larger angle of
>rotation (22 degrees was the most I ever achieved). I hope this
>Adam Beehler

From Fri Feb 22 11:52:57 2008