3D confinement of the focal spot of plasmonic Fresnel zone plate lens using gold bowtie nanoantenna

By using a gold bowtie nanoantenna at the focal plane of a plasmonic Fresnel zone plate lens, we numerically demonstrate that the focused beam spot can be strongly confined in a three-dimensional (3D) region, which means the focal spot will have high axial resolution as well as high lateral resolution. According to the antenna's resonance spectrum, the Fresnel zone plate lens is designed at the resonance wavelength of the antenna to get the right diffractive efficiency, and then the antenna will be positioned at the focal plane, so the 3D confined focal spot can be achieved with much higher intensity and much smaller spot size along both axial and transverse directions than that of a lens without using antennas.