Ultralong pure longitudinal magnetization needle induced by annular vortex binary optics.

In this Letter, based on the Richards and Wolf diffraction theory, an ultralong optical needle with pure transverse polarization is numerically generated by tightly focusing an azimuthally polarized beam through an annular vortex binary filter. Such an ultralong transversely polarized optical needle is generated through the π phase shift between adjacent rings of the binary filter. We show that such a pure transverse optical needle can induce pure longitudinal magnetization with a subwavelength lateral size (0.38λ) and an ultralong longitudinal depth (7.48λ) through the inverse Faraday effect. The corresponding needle aspect ratio of 20 is twice as large as that of the longitudinal magnetization needle generated by electron beam lithography.