Fabrication of self-standing binary Gabor zone plate and its single order diffraction

Abstract

The Gabor zone plate is an ideal zone plate with single focus spot, which has the potential applications in spectroscopy, X-ray imaging, etc. However, the Gabor zone plate is very difficult to prepare because of its sinusoidal transmission characteristic, thereby restricting its applications. Traditionally, the zone plate is prepared on the transparent substrate such as quartz glass, polyimide, etc. This restricts the applications of Gabor zone plates in the extreme ultraviolet and soft X-ray frequency band due to the strong absorption of quartz and polyimide in such bands.In this work, we report a method of preparing the self-standing binary Gabor zone plate by using the focused ion beam direct writing. By combining the techniques of focused ion beam and chemical wet etching, the binary Gabor zone plate with self-standing and curved structure is fabricated. The main characteristic parameters of the Gabor zone plate are as follows: the diameter of 1400 m, the radius of the first zone 90 m, the outset zone number of 60, and a gold absorber thickness of 500 nm. The focusing properties of the self-standing binary Gabor zone plate are measured at different transfer distances with a 355 nm laser. The experimental results show that the high-order focus is removed with only the first-order focus spot reserved, and the focal distance is 2.28 cm, which is in agreement with the theoretical value of 2.41 cm. The self-standing Gabor zone plate is free from the influence of the substrate. Therefore, this kind of binary Gabor zone plate has potential applications in ultraviolet and soft X-ray regions.