Any light that hits the film from free space at a 90-degree angle, known as the normal, will get coupled into a SPP (this part works like a diffraction grating coupler), and that SPP will be heading towards the center of the circles, which is the focal point.
[3] In 2007, a novel, or technologically new, plasmonic lenses and waveguide by modulating light a mesoscale dielectric structure on a metallic film with arrayed nano-slits, which have constant depth but variant widths.
[4] The slits transport electromagnetic energy in the form of SPPs in nanometer sized waveguides and provide desired phase adjustments for manipulating the beam of light.
[5] These devices have been suggested for various applications that take advantage of the small size and high intensity of the SPPs at the focal point.
These include photolithography,[2] heat-assisted magnetic recording, microscopy, biophotonics, biological molecule sensors, and solar cells, as well as other applications.