High efficiency multilevel phase-type Fresnel zone plates produced by two-photon polymerization of SU-8

In this paper, we report on high quality two-level phase-type Fresnel zone plates (FZPs) produced by femtosecond laser two-photon polymerization of the resin SU-8. The optical focusing property was tested using a simple experimental setup. In order to further enhance the diffraction efficiency, four-level and eight-level FZPs were designed using theoretical calculation and rapidly realized by point-to-point femtosecond laser scanning. In this way, the diffractive efficiency was enhanced from 35.8% for the two-level phase lens to 67% for the four-level phase lens and 73.9% for the eight-level phase lens, which are the largest values reported so far