Theory and method for large electric field intensity enhancement in the nanoantenna gap

We first investigate the field intensity in the nanoantenna gap as a function of common antenna properties including polarization, input resistance, and gain. This function provides us a method on how to effectively enhance the field intensity. In the case of polarization matched to the incident wave, the nanoantenna should have both large input resistance and high gain in the arrival direction. To meet these demands, the flat feed gap is modified to a bowtie form, and a hemispherical lens is attached to the nanoantenna. Consequently, the relative field intensity in the gap is found to be 2.6×103  a.u., which is about 8 times larger than the original value, and they all agree well with the simulations. This research is expected to be used as guidelines for the design of nanoantennas and to promote them in plasmonic applications such as spectroscopy and photodetection.