自支撑二值化Beynon-Gabor波带片的制备及其单级聚焦特性

Gabor波带片是一种理想的单级聚焦光学元件,但制备困难.本文采用聚焦离子束直写技术成功制备出30环、20扇区的二值化Beynon-Gabor波带片,其有效面积半径为700μm,第一环半径90μm.利用各向异性腐蚀液对硅基底进行开孔,实现了Beynon-Gabor波带片二值化、自支撑、镂空的结构特征.在波长为355 nm的激光下测试其光学性能,结果表明所制备的Beynon-Gabor波带片主光轴上只存在1级衍射叠加后的焦点,不存在高级衍射焦点,具有优异的单级聚焦性能.

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

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 μm, the radius of the first zone 90 μm, 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.