Investigation of the suitability of RSA-501 as a bulk material for ruling of planar diffraction gratings

This paper investigates the performance of ruled diffraction gratings in the bulk material RSA-501. RSA-501 is a rapidly solidified aluminium alloy with an ultra-fine grain structure that meets the optical and nano-structuring requirements. The aim is to investigate ruled diffraction gratings of RSA-501 regarding their diffraction efficiency, stray light, and structure. Individual grooves, groove arrays, and whole diffraction gratings were fabricated using ruling. Using the bulk material RSA-501 instead of a coating has the advantage that sample preparation by means of flycutting and ruling can be carried out on the same ultra-precision machine tool. This eliminates the need for the cost-intensive and time-consuming preparation of the workpiece by polishing and coating, and avoids re-mounting errors, as a monolithic fabrication is possible. The generated structures were measured by AFM, SEM, and a self-developed optical measuring setup. Results show RSA-501’s suitability for ruled diffraction gratings, with a roughness of the blaze facets that matches the diamond tool’s roughness. Deviations in the vertical positions of groove valleys were identified, which are mainly responsible for the stray light. Ruling performed with shallow blaze angles α ≤ 3° led to a rounding of the blaze facets. This rounding was also observed for individual grooves with larger blaze angles of α ≥ 4°, but the rounding did not occur when the structures were produced in an array. The structure quality and diffraction efficiency of ruled diffraction gratings in RSA-501 lie between those of shaped gratings and gratings produced in complex and less economical ruling process chains. Rapidly solidified aluminium RSA-501 is suitable for ruling diffraction gratings Using a bulk material allows ruling and the sample preparation on the same machine Efficiency lies between shaped gratings and thin-film ruling process chains Stray light results from the deviation of the groove valley position Ruling of small blaze angles α ≤ 3° result in a rounding of the blaze facets