Abstract
We propose to use a pure-phase filter in combination with a high NA lens axicon to achieve a sub-wavelength magnetic focal spot with large uniform magnetization depth when illuminated by a circularly polarized beam. The magnetization distributions are derived and evaluated based on the vector diffraction theory and the inverse Faraday effect of the isotropic and non-magnetically ordered material. With this kind of system, the longitudinal magnetization depth is increased to 12.82λ and the magnetic spot size has been reduced to 0.38λ. However, in the conventional lens with the same NA, the FWHM of the magnetic spot is found to be 0.43λ and its corresponding magnetization depth is only 0.89λ. We expect such a sub-wavelength strong longitudinal magnetic field with large magnetization depth can be widely used in high density magneto-optic recording and the scanning near-field magnetic microscope for studies of magnetic responses of sub-wavelength elementary cells of metamaterials.
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