A beam of light has radial polarization if at every position in the beam the polarization (electric field) vector points towards the centre of the beam. In practice, an array of waveplates may be used to provide an approximation to a radially polarized beam. In this case the beam is divided into segments (eight, for example), and the average polarization vector of each segment is directed towards the beam centre.
Radial polarization can be produced in a variety of ways. It is possible to use a liquid crystal device to convert the polarization of a beam to a radial state, or a radially polarized beam can be produced by a laser in which the Brewster window is replaced by a cone at Brewster's angle. A related concept is azimuthal polarisation, in which the polarisation vector is tangential to the beam. If a laser is focused along the optic axis of a birefringent material, the radial and azimuthal polarizations focus at different planes. A spatial filter can be used to select the polarization of interest
It has been shown that a radially polarized beam can be used to increase the information capacity of free space optical communication via mode division multiplexing, and radial polarization can "self-heal" when obstructed.
- Saito, Y.; Kobayashi, M.; Hiraga, D.; Fujita, K.; et al. (March 2008). "z-Polarization sensitive detection in micro-Raman spectroscopy by radially polarized incident light". Journal of Raman Spectroscopy 39: 1643. Bibcode:2008JRSp...39.1643S. doi:10.1002/jrs.1953.
- "Radial-Azimuthal Polarization Converter". Retrieved 2008-09-30.
- Kozawa, Yuichi; Sato, Shunichi (2005). "Generation of a radially polarized laser beam by use of a conical Brewster prism". Optics Letters 30 (22): 3063–3065. Bibcode:2005OptL...30.3063K. doi:10.1364/OL.30.003063. PMID 16315722.
- Erdélyi, Miklós; Gajdátsy, Gábor (2008). "Radial and azimuthal polarizer by means of a birefringent plate". Journal of Optics A: Pure and Applied Optics 10 (5): 055007. Bibcode:2008JOptA..10e5007E. doi:10.1088/1464-4258/10/5/055007.
- Quabis, S.; Dorn, R.; Muller, J.; Rurimo, G.K.; et al. (2004). Radial polarization minimizes focal spot size. Quantum Electronics Conference 2004 (IQEC) (Washington, OSA, Optical Society of America: Optical Society of America). pp. 615–616. doi:10.1109/IQEC.2004.242867. ISBN 1-55752-778-4.
- Qiwen Zhan (2004). "Trapping metallic Rayleigh particles with radial polarization". Optics Express 12 (15): 3377–3382. Bibcode:2004OExpr..12.3377Z. doi:10.1364/OPEX.12.003377. PMID 19483862.
- Giovanni Milione; et al. (2015). "4 × 20 Gbit/s mode division multiplexing over free space using vector modes and a q-plate mode (de)multiplexer". Optics Letters 40 (9): 1980–1983. arXiv:1412.2717. Bibcode:2015OptL...40.1980M. doi:10.1364/OL.40.001980.
- Giovanni Milione; et al. (2015). "Measuring the self-healing of the spatially inhomogeneous states of polarization of vector Bessel beams". Journal of Optics 17 (3): 1–7. Bibcode:2015JOpt...17c5617M. doi:10.1088/2040-8978/17/3/035617.
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