High-purity longitudinal needle-shaped magnetization fields produced in uniaxial crystals

Based on the Richard-Wolf vector diffraction theory and the inverse Faraday effect, a method of generating a high-purity longitudinal needle-shaped magnetization field in the uniaxial crystal is proposed. In this method, the inverse radiation of the electric dipole in the uniaxial crystal is used to construct an optimal entry pupil light field through regulating the multi-parameter of the number of electric dipole pairs N and their array, and then the magnetization field of the desired target is obtained by forward tightly focusing. The simulation results show that when N = 1, the focal length of the magnetic field generated in the uniaxial crystal increases by 1.4 times and the lateral resolution increases by 5% compared with the counterparts in an isotropic medium. It can be further seen that when N = 2 and N = 3, with the increase of the number of electric dipole pairs, the focal length of the needle magnetic field generated in the uniaxial crystal increases by 10%, and the lateral resolution increases by 18%. The purity of the needle magnetic field gradually increases to 1 as the magnetization field profile surface value changes from 0.1 to 1. Especially when N = 2 and the contour surface value is 0.1, the magnetic field purity is as high as 95%. The results provide a feasible scheme for generating a longitudinal magnetization field with higher purity and longer focal length in an anisotropic medium, and also present the theoretical guidance for selecting optimal pupil beams in practical applications such as all-optical magnetic recording, atom capture and lithography.