Khonina Svetlana N, Volotovsky Sergey G
Image Processing Systems Institute of the RAS, Molodogvardeiskaya Street 151, Samara 443001, Russia.
J Opt Soc Am A Opt Image Sci Vis. 2010 Oct 1;27(10):2188-97. doi: 10.1364/JOSAA.27.002188.
We show that the contribution of the electric field components into the focal region can be controlled using binary phase structures. We discuss differently polarized incident waves, for each case suggesting easily implemented binary phase distributions that ensure a maximum contribution of a definite electric field component on the optical axis. A decrease in the size of the central focal spot produced by a high numerical aperture (NA) focusing system comes as the result of the spatial redistribution of the contribution of different electric field components into the focal region. Using a polarization conversion matrix of a high NA lens and the numerical simulation of the focusing system in Debye's approximation, we demonstrate benefits of using asymmetric to polar angle ϕ binary phase distributions (such as arg[cos ϕ] or arg[sin 2ϕ]) for generating a subwavelength focal spot in separate electric field components. Additional binary structure variations with respect to the azimuthal angle also make possible controlling the longitudinal distribution of light. In particular, the contribution of the transverse components in the focal plane can be reduced by the use of a simple axicon-like structure that serves to enhance the NA of the lens central part, redirecting the energy from focal plane. As compared with the superimposition of a narrow annular aperture, this approach is more energy efficient, and as compared with the Toraldo filters, it is easier to control when applied to three-dimensional focal shaping.
我们表明，利用二元相位结构可以控制电场分量对焦区的贡献。我们讨论了不同偏振的入射波，针对每种情况提出了易于实现的二元相位分布，以确保在光轴上特定电场分量的最大贡献。高数值孔径（NA）聚焦系统产生的中央焦斑尺寸减小，是不同电场分量对焦区贡献的空间重新分布的结果。利用高NA透镜的偏振转换矩阵以及在德拜近似下对聚焦系统的数值模拟，我们展示了使用相对于极角ϕ不对称的二元相位分布（如arg[cos ϕ]或arg[sin 2ϕ]）在单独的电场分量中产生亚波长焦斑的优势。相对于方位角的额外二元结构变化也使得控制光的纵向分布成为可能。特别是，通过使用一种简单的类似轴锥的结构，可以减少焦平面中横向分量的贡献，该结构用于增强透镜中心部分的NA，将能量从焦平面重新定向。与窄环形孔径的叠加相比，这种方法更节能，与托拉尔多滤波器相比，应用于三维焦斑整形时更容易控制。
