Determination of Electric-Field, Magnetic-Field, and Electric-Current Distributions of Infrared Optical Antennas: A Near-Field Optical Vector Network Analyzer

Abstract

In addition to the electric field $\mathbit{E}(\mathbit{r})$, the associated magnetic field $\mathbit{H}(\mathbit{r})$ and current density $\mathbit{J}(\mathbit{r})$ characterize any electromagnetic device, providing insight into antenna coupling and mutual impedance. We demonstrate the optical analogue of the radio frequency vector network analyzer implemented in interferometric homodyne scattering-type scanning near-field optical microscopy for obtaining $\mathbit{E}(\mathbit{r})$, $\mathbit{H}(\mathbit{r})$, and $\mathbit{J}(\mathbit{r})$. The approach is generally applicable and demonstrated for the case of a linear coupled-dipole antenna in the midinfrared spectral region. The determination of the underlying 3D vector electric near-field distribution $\mathbit{E}(\mathbit{r})$ with nanometer spatial resolution and full phase and amplitude information is enabled by the design of probe tips with selectivity with respect to ${E}_{\ensuremath{\parallel}}$ and ${E}_{\ensuremath{\perp}}$ fabricated by focused ion-beam milling and nano-chemical-vapor-deposition methods.