Measuring the magnetic topological spin structure of light using an anapole probe

Abstract

Topological spin structures of light, including the Skyrmion, Meron, and bi-Meron, are intriguing optical phenomena that arise from spin–orbit coupling. They have promising potential applications in nano-metrology, data storage, super-resolved imaging and chiral detection. Aside from the electric part of optical spin, of equal importance is the magnetic part, particularly the H-type electromagnetic modes for which the spin topological properties of the field are dominated by the magnetic field. However, their observation and measurement remains absent and faces difficult challenges. Here, we design a unique type of anapole probe to measure specifically the photonic spin structures dominated by magnetic fields. The probe is composed of an Ag-core and Si-shell nanosphere, which manifests as a pure magnetic dipole with no electric response. The effectiveness of the method was validated by characterizing the magnetic field distributions of various focused vector beams. It was subsequently employed to measure the magnetic topological spin structures, including individual Skyrmions and Meron/Skyrmion lattices for the first time. The proposed method may be a powerful tool to characterize the magnetic properties of optical spin and valuable in advancing spin photonics.

High-resolution imaging of 3D stray-field components with a Fe3O4 nanoparticle sensor

“…Understanding the mechanism of nanomagnetism underpins the development of future spintronic devices. [1][2][3][4][5][6][7][8][9][10][11][12] The development of magnetic imaging techniques, including scanning transmission X-ray microscopy, magneto-optical Kerr microscopy, Lorentz microscopy, resonant magnetic X-ray imaging, nanoprobe-based near-field mapping, and optical near-field imaging, [13][14][15][16][17][18] have facilitated the research on nanoscale spin-textures for spintronic applications. Additionally, recent advances in near-field Brillouin light scattering, timeresolved X-ray microscopy etc.…”

Three Orthogonal Polarization Distribution Mapping of the Tightly Focused Fields with a Dual‐Mode Waveguide Probe

“…[6][7][8] The investigations into these exceptional characteristics have uncovered various intriguing physical phenomena, e.g., spin-to-orbit angular momentum conversion, [9][10][11][12] the spin dependent unidirectional emission, [13][14][15][16] and photonic skyrmions. [17][18][19][20][21][22][23][24] These phenomena have also led in turn to practical applications including microscopic imaging, [25][26][27][28] nanoparticle manipulation, [29][30][31][32] and displacement sensing. [33][34][35] Characterization of all three orthogonal polarized components is absolutely essential for research into the physical mechanisms of focused EM fields and related applications.…”

“…[ 6–8 ] The investigations into these exceptional characteristics have uncovered various intriguing physical phenomena, e.g., spin‐to‐orbit angular momentum conversion, [ 9–12 ] the spin dependent unidirectional emission, [ 13–16 ] and photonic skyrmions. [ 17–24 ] These phenomena have also led in turn to practical applications including microscopic imaging, [ 25–28 ] nanoparticle manipulation, [ 29–32 ] and displacement sensing. [ 33–35 ]…”

光学自旋角动量的调控机理及研究进展（特邀）

“…7 Nanoparticle-film structures for the detection of spin angular momentum. (a) Two excitation methods of nanogold particle-gold film structure [156] ; (b) optical response of PS nanoparticles [102] ; (c) Ag core-Si shell probe particles used for detecting magnetic field components and the electromagnetic response curves of the particles [91] ; (d) schematic of the coupling process between tightly focused beam and nanoparticle waveguide structure and Fresnel coefficients for different modes in this structure [104] 1026002 -10 8 Spin angular momentum detection system based on nonlinear effects. (a) Optical path configuration of nonlinear nearfield optical microscopy [99] ; (b) circular coupled grating structure for exciting SPP [99] ; (c) nearfield distribution obtained by illuminating the grating with lefthanded and righthanded circularly polarized pump beams and their differential result…”