Characterization of focusing performance of spiral zone plates with fractal structure

Zang Hua-Ping¹, Zheng Cheng-Long¹, Ji Zi-Wen¹, Fan Quan-Ping², Wei Lai², Li Yong-Jie³, Mu Kai-Jun¹, Chen Shu¹, Wang Chuan-Ke², Zhu Xiao-Li⁴, Xie Chang-Qing⁴, Cao Lei-Feng^{2, †}, Liang Er-Jun^{1, ‡}

(a) Schematic flow chart of fabrication process of FSZPs which consists of 1 chromium layer and photoresist coatings, 2 exposure, 3 chromium etching, and 4 resist removal; (b) microscopic image of fabricated FSZP sample.