We consider two kinds of plasmonic nanolenses which focus radially polarized Laguerre-Gauss beam into
subwavelength spot. The first one is free-standing opaque metal layer with concentric grooves on both sides [Phys. Rev.
Lett. 102, 183902 (2009)]. The second has slits instead of grooves thus concentric rings have to be integrated with
dielectric matrix. Constructive interference of far-field radiation of SPPs scattered on the back side of the lenses gives
subwavelength size foci approaching the Rayleigh resolution limit. We investigate transmission and focusing properties
of considered metal structures. Choice of appropriate metal such as silver, gold, copper or aluminum strongly affects
transmission. Parameters of surface structure determine efficient photon-plasmon coupling and plasmon scattering
phenomenon thus influence both transmission and focusing effect. Finally, the choice of dielectric function of
surrounding medium gives another degree of freedom to fulfill momentum matching condition for resonant photonplasmon
interaction. In this paper, taking into account the above parameters, we show an optimization procedure, which
leads to high transmission, tight focal spot and large focal length of the considered plasmonic nanolenses.
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