Subwavelength focusing of laser light using a chromium zone plate

Anton Gennadyevich Nalimov, Samara National Research University
Sergey Sergeevich Stafeev, Samara National Research University
Elena Sergeevna Kozlova, Samara National Research University
Victor Victorovich Kotlyar, Samara National Research University
Liam O’Faolain, University of St Andrews
Maria V. Kotlyar, Federal Scientific Research Center "Crystallography and photonics" of Russian Academy of Sciences


© 2017, Institution of Russian Academy of Sciences. All rights reserved. We study in which way the parameters of a focal spot generated by a chromium zone plate 15-μm in diameter synthesized by sputtering on a glass substrate and having a focal length equal to the incident wavelength of λ = 532 nm depend on the microrelief height. It is shown numerically that an optimal microrelief height of the zone plate is 70 nm. With these parameters, the minimal size of the focal spot is achieved. Using a scanning near field optical microscope the said zone plate is shown to focus a linearly polarized Gaussian beam into an elliptical focal spot having the fullwidth at half-maximum of FWHMx = 0.42λ and FWHMy = 0.64λ along the Cartesian axes.