We excite a guided plasmonic mode in slot waveguides of subwavelength width. With a phase- and polarization-sensitive near-field microscope, we measure the electric field of the mode for a range of slot widths from 40 to 120 nm. The field is experimentally found to be antisymmetric across the slot gap. Numerical calculations confirm this symmetry. Calculations also show a confinement of the field to a lateral size ∼10 times smaller than the free-space wavelength.

Appl. Phys. Lett.

Spasenović, M., van Oosten, D., Verhagen, E., & Kuipers, K. (2009). Measurements of modal symmetry in subwavelength plasmonic slot waveguides. Appl. Phys. Lett., 95(Article number: 203109), 1–3. doi:10.1063/1.3254246