Near-field probing the magnetic field vector of visible light with a silicon nanoparticle probe and nanopolarimetry.

Abstract

Magnetic light-matter interaction plays a crucial role in nanophysics, such as in photonic topological insulators and metamaterials. Recent advances in all-dielectric nanophotonics especially demand vectorial mapping of magnetic light at visible wavelengths. Here, we report that a novel functional nanoprobe decorated with a silicon nanoparticle predominantly senses both the vertical and lateral magnetic field, that is, the magnetic field vector, complementary to a metal nanoparticle probe detecting the local electric field vector. As a proof-of-principle experiment, we demonstrate the mapping of magnetic field vectors in a transverse electric (TE) evanescent standing wave by this probe in a scanning near-field optical microscope (SNOM) with nanopolarimetry. It is for the first time that the full magnetic field vector of visible light, whose frequency exceeds 550 THz, can be directly detected with deep subwavelength resolution. Such functional probe and nanopolarimetry may pave the way toward complete vectorial near-field characterization over the whole visible band for nano-optics and subwavelength optics.