High-quality longitudinally polarized photonic nanojet created by a microdisk.

The Letter reports the generation of a high-quality longitudinally polarized photonic nanojet by illuminating a dielectric microdisk with a focused radially polarized light. High-quality longitudinally polarized beams can be generated using a microdisk with a wide range of refractive indices. By optimizing the shape and refractive index of the microdisk, the radial component can be effectively suppressed, and a maximum beam quality of 90% and a field enhancement factor of up to two orders can be achieved with a sub-diffraction-limited spot size. Moreover, the focusing performance of the microdisk is observed to be stable within a wide range of focusing numerical aperture values of the incident light.