| 摘要 |
A free-electron laser system and optical polarization conversion are provided for producing azimuthal polarization and radial polarization laser beams. The free-electron laser system includes a helical wiggler for generating a transverse magnetic field around a beam axis. An electron beam is projected along the beam axis and interacts with the transverse magnetic field so as to induce spontaneous and stimulated emission of optical radiation. A resonator cavity is formed by a pair of mirrors in which the optical radiation oscillates therein. The laser system directly produces an azimuthal polarization laser beam as an output. The laser system may further be coupled to an optical polarization converter which includes a pair of optical half-wave plates having a forty-five degree (45 DEG ) optical axis difference therebetween. The azimuthal polarization laser beam is transmitted through the optical polarization converter so as to generate a radial polarization output beam. The optical polarization converter may further operate as a bi-directional optical polarization converter for converting between azimuthal polarization and radial polarization laser beams. In addition, optical polarization converter may further operate with other optical axis differences so as to provide a general polarization rotator for rotating polarization according to directions based on selected arbitrary angles.
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