Is it a half wave plate?

Published on: Tue Mar 08 2011

There is a small square of glass at the Laser Teaching Center, and Dr Noe and I thought it could be a wave plate (either ½ or ¼) but we were not sure. I investigated how it interacted with a laser and two linear polarizers to find out.

The laser was a red HeNe 5mw, initially non-polarized (Checked by rotating two linear polarizers in the beam, resulting in no dot). The beam traveled through a linear polarization filter (Dichroic plastic… FYI to self; Remember Dichroic glass) and emerged linearly polarized. A second polarizer, rotated 90 degrees, was placed in front of the viewing screen completely eliminating the dot.

***Note*** I did not have a tool for measuring intensity at the time, so I judged intensity on a scale of “no dot”, “medium dot”, “bright dot”. Next week I will see about exactly measuring the intensity of the dot.

I added the glass square in between the two polarization filters. For most of the rotation positions the dot became visible again. The only time it did not alter the state of the dot (no dot) was at four 90 rotations of itself.

The next question was if it was a ½ waveplate or quarter waveplate, to examine this I wanted to check for circular or elliptical polarization.