Shaped vibration cutting: A novel fabrication method for mid-infrared relief gratings with controllable profiles

Abstract

Relief gratings are a particular group of diffractive gratings with a controlled profile, which can precisely modulate the intensity distribution of diffractive lights through its surface structure of depressions and elevations. The mechanical ruling is still one of the most dominant methods for fabricating relief gratings due to its accuracy and capacity to texture free-formed surfaces. However, the ruling has the drawbacks of low material adaptability and inflexible profile adjustability that restrict its wider application. This study invents a novel ruling process, i.e., shaped vibration cutting (SVC), which uses a controllable special-shaped vibration locus of a diamond cutting tool. The tool moves perpendicularly to the cutting plane, enabling the ruling-based fabrication of relief grating on difficult-to-cut materials with flexible control of the grating profile. Slope grooving tests with elliptical and triangular trajectories were performed on aluminum and silicon materials to explore the surface generation and defect formation mechanism comprehensively. The defect-less process window regarding the vibration trajectory, crossfeed, depth of cut, and ruling velocity was identified. Finally, mid-infrared relief gratings were successfully fabricated using the SVC process on aluminum without burrs and silicon in a ductile regime with a maximum depth of 2.3 µm, which outperforms the existing cutting-based texturing technique. To further demonstrate the process capacity of SVC in high material adaptability and flexible profile adjustability, multi-blaze gratings that have spatially varying groove profiles have been fabricated on bulk metallic glass.