Unpolarized Single-Frequency Output
Posted on 2008-09-10 as a part of the Photonics Spotlight (available as e-mail newsletter!)
Permanent link: https://www.rp-photonics.com/spotlight_2008_09_10.html
Author: Dr. Rüdiger Paschotta, RP Photonics Consulting GmbH
Abstract: Unpolarized emission of a laser is a necessarily stochastic phenomenon, which cannot occur for a strictly monochromatic beam.
Ref.: encyclopedia articles on polarization of light, single-frequency lasers
Did you ever encounter a single-frequency laser with truly unpolarized output? This question is a lot more tricky than it may seem. At least for strictly monochromatic emission, some defined polarization state is actually unavoidable, i.e., unpolarized emission is impossible. For any monochromatic laser beam propagation in z direction, the complex field amplitude Ex and Ey for oscillation in the two transverse directions must have some constant values, and depending on their magnitudes and phases, the polarization is either linear in some direction, or elliptical, or circular. Unpolarized emission is a necessarily stochastic phenomenon, which implies an optical spectrum which cannot be described with a delta function.
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