One way to make a linearly polarized beam rotating at frequency $\Delta f\approx10\mbox{MHz}$ is by combining two circularly polarized beams, one left-handed and one right-handed, and where one beam is at a frequency $f$ and the other at $f\pm\Delta f$. Is there another way to do this using only a single beam passed through some active optical device (eg electro-optic-modulator)? I'm interested in the mid-infrared (10.6um).
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1$\begingroup$ Just put a polarizing filter there and rotate it with an electric motor, if you don't need very high rotation frequency that would do what you want. $\endgroup$– Maxim UmanskyOct 14, 2014 at 16:59
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1$\begingroup$ Unfortunately I would need frequency of about 10MHz. I'll edit the question. $\endgroup$– cpc333Oct 14, 2014 at 18:10
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2 Answers
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A Pockel cell followed by a quarter waveplate will do this. The Pockel cell acts as an electrically controlled waveplate which will give an elliptical state. The waveplate will then convert this to a rotated linear state. Producing a 10MHz driving signal at the several kilovolts required might be a challenge but not impossible.
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Faraday Effect. The plane of polarization in a medium is rotated when exposed to a magnetic field. Solenoid, glass rod.