Document Type



Atomic, Molecular and Optical Physics | Optics | Physical Sciences and Mathematics | Physics

Publication Details

Applied Physics Letters, 14(14) (2019). This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared as Victor V. Kotlyar, Sergey S. Stafeev, Anton G. Nalimov and Liam O'Faolain, "Subwavelength grating-based spiral metalens for tight focusing of laser light", Applied Physics Letters 114, 141107 (2019) and may be found at https://doi.org/10.1063/1.5092760.


In this paper, we investigate a 16-sector spiral metalens fabricated on a thin film (130 nm) of amorphous silicon, consisting of a set of subwavelength binary diffractive gratings and with a numerical aperture that is close to unity. The metalens converts linearly polarized incident light into an azimuthally polarized optical vortex and focuses it at a distance approximately equal to the wavelength of the incident light, k ¼ 633 nm. Using a scanning near-field optical microscope, it is shown experimentally that the metalens forms an elliptical focal spot with diameters smaller than the diffraction limit: FWHMx ¼ 0.32k (60.03k) and FWHMy ¼ 0.51k (60.03k). The experimental results are close to those of a numerical simulation using the FDTD method, with FWHMx ¼ 0.37k and FWHMy ¼ 0.49k. The technological errors due to manufacturing were taken into account in the simulation. This is the smallest focal spot yet obtained with a metalens.