Creation of an ultra-long depth of focus super-resolution longitudinally polarized beam with a ternary optical element

We proposed a method to design a ternary optical element in order to achieve a needle of super-resolution longitudinally polarized beam with ultra-long depth of focus, and obtained a beam with a size of 0.3995λ and depth of focus of 12.83λ after focusing a ternary optical element modulated, radially polarized Bessel–Gaussian beam with an aplanatic lens of numerical aperture 0.95. The algorithm we used to design the ternary optical element is based on axial uniformity in the focal region, which allows rapid searching speeds and excellent performance. The ratio of pupil radius to the beam waist was set as 0.57, making the peak intensity of the incident beam occur at the rim of the lens aperture, which maximized the possible resolution of the focused beam.