Laser ablation of high-aspect-ratio hole arrays in tungsten for X-ray applications

Abstract

Periodic two-dimensional tungsten X-ray optical gratings were fabricated using a combination of pico-second laser ablation and wet chemical etch. A 200 μm thick cold-rolled sheet of tungsten (99.97%) was used as base material for the fabrication of a 1.5 × 1.5 cm2 periodic grating with an array of circular holes of approximately 12:1 aspect ratio. The laser parameters were optimized to obtain through-hole diameters slightly smaller than the desired final dimension. Subsequent wet etching was used to precisely control the diameter of through-holes. The through-hole profile was characterized using scanning electron microscopy (SEM) and showed a slight conical shape with a slope of 1.3%. The two-dimensional tungsten absorption grating was successfully tested in an X-ray phase-contrast imaging setup. The method has proven to have some relevant benefits, such as good reproducibility and fairly easy fabrication due to few manufacturing steps.