All-Dielectric Nanophotonics Enables Tunable Excitation of the Exchange Spin Waves.

Launching and controlling magnons with laser pulses opens up new routes for applications including optomagnetic switching and all-optical spin wave emission and enables new approaches for information processing with ultralow energy dissipation. However, subwavelength light localization within the magnetic structures leading to efficient magnon excitation that does not inherently absorb light has still been missing. Here, we propose to marriage the laser-induced ultrafast magnetism and nanophotonics to efficiently excite and control spin dynamics in magnetic dielectric structures. We demonstrate that nanopatterning by a 1D grating of trenches allows localization of light in spots with sizes of tens of nanometers and thus launch the exchange standing spin waves of different orders. The relative amplitude of the exchange and magnetostatic spin waves can be adjusted on demand by modifying laser pulse polarization, incidence angle, and wavelength. Nanostructuring of the magnetic media provides a unique possibility for the selective spin manipulation, a key issue for further progress of magnonics, spintronics, and quantum technologies.

Magneto-optics of subwavelength all-dielectric gratings.

We provide the experimental research on a novel type of all-dielectric magnetic structure designed to achieve an enhanced magneto-optical response. 1D grating fabricated via etching of bismuth substituted iron garnet film supports the excitation of optical guided modes, which are highly sensitive to the external magnetic field. A unique feature of proposed structure is the synergetic combination of high transparency, tunability, high Q-factor of the resonances and superior magneto-optical response that is two orders higher in magnitude than in the non-structured smooth iron-garnet film. The considered all-dielectric magnetic garnet structures have great potential in various fields including the magneto-optical modulation of light, biosensing and magnetometry.

All-dielectric magnetic metasurface for advanced light control in dual polarizations combined with high-Q resonances.

Nanostructured magnetic materials provide an efficient tool for light manipulation on sub-nanosecond and sub-micron scales, and allow for the observation of the novel effects which are fundamentally impossible in smooth films. For many cases of practical importance, it is vital to observe the magneto-optical intensity modulation in a dual-polarization regime. However, the nanostructures reported on up to date usually utilize a transverse Kerr effect and thus provide light modulation only for p-polarized light. We present a concept of a transparent magnetic metasurface to solve this problem, and demonstrate a novel mechanism for magneto-optical modulation. A 2D array of bismuth-substituted iron-garnet nanopillars on an ultrathin iron-garnet slab forms a metasurface supporting quasi-waveguide mode excitation. In contrast to plasmonic structures, the all-dielectric magnetic metasurface is shown to exhibit much higher transparency and superior quality-factor resonances, followed by a multifold increase in light intensity modulation. The existence of a wide variety of excited mode types allows for advanced light control: transmittance of both p- and s-polarized illumination becomes sensitive to the medium magnetization, something that is fundamentally impossible in smooth magnetic films. The proposed metasurface is very promising for sensing, magnetometry and light modulation applications.

Nonreciprocal Transverse Photonic Spin and Magnetization-Induced Electromagnetic Spin-Orbit Coupling.

We present a formulation of electromagnetic spin-orbit coupling in magneto-optic media, and propose an alternative source of spin-orbit coupling to non-paraxial optics vortices. Our treatment puts forth a formulation of nonreciprocal transverse-spin angular-momentum-density shifts for evanescent waves in magneto-optic waveguide media. It shows that magnetization-induced electromagnetic spin-orbit coupling is possible, and that it leads to unequal spin to orbital angular momentum conversion in magneto-optic media evanescent waves in opposite propagation-directions. Generation of free-space helicoidal beams based on this conversion is shown to be spin-helicity- and magnetization-dependent. We show that transverse-spin to orbital angular momentum coupling into magneto-optic waveguide media engenders spin-helicity-dependent unidirectional propagation. This unidirectional effect produces different orbital angular momenta in opposite directions upon excitation-spin-helicity reversals.