We demonstrate an all-optical strategy for realizing spherical three-dimensional (3D) super-resolution (∼λ3/22) spot arrays of pure longitudinal magnetization by exploiting a 4π optical microscopic setup with two high numerical aperture (NA) objective lenses, which focus and interfere two modulated vectorial beams. Multiple phase filters (MPFs) are designed via an analytical approach derived from the vectorial Debye diffraction theory to modulate the two circularly polarized beams. The system is tailored to constructively interfere the longitudinal magnetization components, while simultaneously destructively interfering the azimuthal ones. As a result, the magnetization field is not only purely longitudinal but also super-resolved in all three dimensions. Furthermore, the MPFs can be designed analytically to control the number and locations of the super-resolved magnetization spots to produce both uniform and nonuniform arrays in a 3D volume. Thus, an all-optical control of all the properties of light-induced magnetization spot arrays has been demonstrated for the first time. These results open up broad applications in magnetic-optical devices such as confocal and multifocal magnetic resonance microscopy, 3D ultrahigh-density magneto-optic memory, and light-induced magneto-lithography.
The light-induced magnetization distributions for a high numerical aperture focusing configuration with an azimuthally polarized Bessel-Gaussian beam modulated by optimized vortex binary filters are investigated based on the inverse Faraday effect. It is found that, by adjusting the radii of different rings of the single/ cascaded vortex binary filters, super-long (12λ) and sub-wavelength (0.416λ) longitudinal magnetization chain with single/dual channels can be achieved in the focal region. Such well-behaved magnetization trait is attributed to the mutual effect between the optical polarization singularities of the azimuthally polarized beam and single/cascaded spiral optical elements. In addition, we find that the displacement distance of the longitudinal magnetization chain is proportional to the phase difference between the inner circle and outer ring of the vortex binary filters, thus giving rise to the steerable magnetization chain. It is expected that the research outcomes can be applied in multiple atoms trapping and transport, multilayer magneto-optical data storage, fabrication of magnetic lattices for spin wave operation and development of ultra-compact optomagnetic devices.
Based on the vector diffraction theory and the inverse Faraday effect, we numerically study the light-induced magnetization near the focus of a 4π high numerical aperture focusing configuration under the illumination of two counter- propagating radially polarized hollow Gaussian vortex beams. The simulated results demonstrate that, by selecting higher-order vortex beam modes (e.g. with – the beam order) and proper truncation parameter (e.g. with – the ratio of the pupil radius to the incident beam waist), spherical and sub-wavelength longitudinal magnetization can be generated in the vicinity of focus. Such special magnetization feature is attributed to not only the interaction between optical vortices and the radially polarized beams, but also the completely destructive interference of azimuthal components and the constructive interference of the longitudinal component of the two counter-propagating radially polarized vortex beams. This spherical and sub-wavelength longitudinal magnetization distribution may be of interest for applications in all-optical magnetic recording and confocal and magnetic resonance microscopy.