Simulation of Tight Focusing of Laser Light by Gold Zone Plate

In this paper amplitude Fresnel zone plates with gold relief on silica glass is investigated by using frequency dependent finite difference time domain method. During the simulation linearly and circularly polarized Gaussian beams with wavelength of 532 nm are proposed as incident light. Study of the focal spot characteristics versus the relief height of zone plate is carried out. It shows that the height of 140 nm allows to achieve an optimal ratio between width and intensity of the focal spot. Also, it is shown that for linear polarized Gaussian beam this gold zone plate gives tighter focal spot with the full width at half maximum of 0.38λ and 0.86λ than phase zone plate and produce circle focal spot with the Cartesian axis diameter of 0.64λ for circularly polarized light.