Light is an electromagnetic wave composed of oscillating electric and magnetic fields, the one never occurring without the other. In light-matter interactions at optical frequencies, the magnetic component of light generally plays a negligible role. When we “see” or detect light, only its electric field is perceived; we are practically blind to its magnetic component. We used concepts from the field of metamaterials to probe the magnetic field of light with an engineered near-field aperture probe. We visualized with subwavelength resolution the magnetic- and electric-field distribution of propagating light.

Burresi, M, van Oosten, D, Kampfrath, T, Schoenmaker, H, Heideman, R, Leinse, A, & Kuipers, L.K. (2009). Probing the magnetic field of light at optical frequencies. Science, 326, 550–553. doi:10.1126/science.1177096