Understanding Circular Polarisation

would take more than a blog post…. but I have found a nice flash animation that does a good job of showing how a 1/4 wave phase retarder can take a linearly polarised beam, and make it circularly polarised (or polarized for the Americans out there).

You can see it here , and there is a good text description too ( D Harrison University of Toronto)

Like most optical systems this is reversible, so it will equally take an incoming circularly polarised beam, and make it linear.

This is what happens with a CO2 laser, when a back reflection off a metal workpiece occurs, and the beam reflects straight back through the beam delivery system the “wrong way”, and possibly straight back into the laser.

At this point I imagine the Jude Law film “Enemy at the gates” where he shoots the sniper through his own rifle sight. Perfect alignment !


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