Angle of Incidence Detection of Long-Wave IR Radiation Using Nanoantennas

We are studying thermoelectrically coupled nanoantennas (TECNAs) to determine the angle of incidence (AOI) of laser beams in the long-wave infrared (LWIR) regime. TECNAs consist of a nanoantenna and a nanothermocouple (NTC) that are fabricated over a quasi-spherical cavity etched into the Si substrate. The antenna nature of the TECNAs makes them polarization and wavelength-selective, and the cavity provides directional selectivity. In this article, we experimentally demonstrate that the far-field radiation pattern of TECNAs is altered by positioning them at various locations above the cavity. Both experimental results and finite element method simulations show that the resulting radiation pattern of the antenna is determined by the nanoantenna’s position relative to the center of the cavity. Additionally, we highlight that the substrate significantly affects the far-field pattern of TECNAs; under coherent excitation, interference patterns overlay the radiation pattern due to back reflection from the substrate. We have shown that this effect is attributed to the substrate, as the interference pattern is negligible under incoherent illumination.