Experimental verification of the super-resolution focusing optical needle and imaging with a new type Fresnel zone plate

This paper presents the experimental demonstration of the mixed Fresnel zone plate (M-FZP) for super-resolution focusing and imaging applications. The M-FZP, with a processing error of 5 nm, is fabricated using focused ion beam etching (FIB). The influence of FIB processing parameters and processing scanning methods on the quality of M-FZP is explored. Results show that the annular scanning processing method, performed from inside to outside, is more suitable for manufacturing M-FZPs. At a wavelength of λ = 633 nm, the planar M-FZP exhibits a focusing optical-needle with the smallest full width at half maximum of 295 nm (0.466 λ) and 283 nm (0.447 λ) in x and y directions, respectively. It also possesses a depth of focus of 3.9μm and a central focal length of 9.073μm. A device based on M-FZP is constructed in combination with confocal technology, and a corresponding experiment is conducted to enable super-resolution imaging. This new microstructure provides a new solution for super-resolution focusing and imaging.