Tight focusing of laser light using a chromium Fresnel zone plate
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Using near-field scanning microscopy, we demonstrate that a 15-µm zone plate fabricated in a 70-nm chromium film sputtered on a glass substrate and having a focal length and outermost zone's width equal to the incident wavelength λ = 532 nm, focuses a circularly polarized Gaussian beam into a circular subwavelength focal spot whose diameter at the full-width of half-maximum intensity is FWHM = 0.47λ. This value is in near-accurate agreement with the FDTD-aided numerical estimate of FWHM = 0.46λ. When focusing a Gaussian beam linearly polarized along the y-axis, an elliptic subwavelength focal spot is experimentally found to measure FWHMx = 0.42λ (estimated value FWHMx = 0.40λ) and FWHMy = 0.64λ. The subwavelength focal spots presented here are the tightest among all attained so far for homogeneously polarized beams by use of non-immersion amplitude zone plates.
Kotlyar , V V , Stafeev , S S , Nalimov , A G , Kotlyar , M V , O'Faolain , L & Kozlova , E S 2017 , ' Tight focusing of laser light using a chromium Fresnel zone plate ' , Optics Express , vol. 25 , no. 17 , pp. 19662-19671 . https://doi.org/10.1364/OE.25.019662
© 2017, Optical Society of America. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1364
DescriptionFunding: Russian Scientific Foundation (17-19-01186).
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