Microlens-aided focusing of linearly and azimuthally polarized laser light

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Stafeev, S. S.
Nalimov, A. G.
Kotlyar, M. V.
Gibson, D.
Song, S.
O'Faolain, Liam
Kotlyar, V. V.
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Optical Society of America (OSA)
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We have investigated a four-sector transmission polarization converter (4-SPC) for a wavelength of 633 nm, that enables the conversion of a linearly polarized incident beam into a mixture of linearly and azimuthally polarized beams. It was numerically shown that by placing a Fresnel zone plate of focal length 532 nm immediately after the 4-SPC, the incident light can be focused into an oblong subwavelength focal spot whose size is smaller than the diffraction limit (with width and breadth, respectively, measuring FWHM = 0.28λ and FWHM = 0.45λ, where λ is the incident wavelength and FWHM stands for full-width at half maximum of the intensity). After passing through the 4-SPC, light propagates in free space over a distance of 300 μm before being focused by a Fresnel zone plate (ZP), resulting in focal spot measuring 0.42λ and 0.81λ. The focal spot was measured by a near-field microscope SNOM, and the transverse E-field component of the focal spot was calculated to be 0.42λ and 0.59λ. This numerical result was verified experimentally, giving a focal spot of smaller and larger size, respectively, measuring 0.46λ and 0.57λ. To our knowledge, this is the first implementation of polarization conversion and subwavelength focusing of light using a pair of transmission micro-optic elements
Binary optics , Microstructure fabrication , Polarization-selective devices , Polarization , Diffractive lenses , Near-field microscopy , Subwavelength structures , Azimuthally polarized beams , Cylindrical vector beams , Electron beam lithography , Laser beams , Light beams , Polarization control
Stafeev, S.S., Nalimov, A.G., Kotlyar, M.V., Gibson, D., Song, S., O’Faolain, L. and Kotlyar, V.V., 2016. Microlens-aided focusing of linearly and azimuthally polarized laser light. Optics express, 24(26), pp. 29800-29813. DOI:10.1364/OE.24.029800