Direct Observation of Lateral Field Confinement in Symmetry-Protected THz Bound States in the Continuum

摘要

Electromagnetic field confinement on sub-wavelength scales is possibleat the expense of increasing optical losses. Examples are surface plasmonpolaritons and resonant structures, which suffer from absorption losses andradiative outcoupling, respectively. Here, the first experimental evidenceof strong electromagnetic field confinement along the lateral (out-of-plane)direction in a near lossless metasurface that supports a symmetry-protectedBound State in the Continuum is shown, which fully suppresses the radiativelosses of resonant scatterers. This experimental demonstration, supported bycoupled dipole calculations, is measured by a double near-field probe techniqueto locally excite and detect the time evolution and confinement of theelectric field onto the surface, achieving an amplitude decay length from themetasurface of λ/38 at 0.39 THz.