Line Spread Functions of Blazed Off-Plane Gratings Operated in the Littrow Mounting

TL;DR

This paper reports on the fabrication and testing of blazed off-plane gratings for X-ray spectroscopy, demonstrating high resolution and efficiency improvements suitable for future space missions.

Contribution

It introduces a scalable microfabrication technique for off-plane gratings with blazed profiles and evaluates their performance in a test facility.

Findings

Maximum resolution of 800 ± 20 achieved.

Evidence of blaze effect observed in efficiency measurements.

Gratings show potential for high-resolution X-ray spectroscopy.

Abstract

Future soft X-ray (10 - 50 Angstrom) spectroscopy missions require higher effective areas and resolutions to perform critical science that cannot be done by instruments on current missions. An X-ray grating spectrometer employing off-plane reflection gratings would be capable of meeting these performance criteria. Off-plane gratings with blazed groove facets operated in the Littrow mounting can be used to achieve excellent throughput into orders achieving high resolutions. We have fabricated two off-plane gratings with blazed groove profiles via a technique which uses commonly available microfabrication processes, is easily scaled for mass production, and yields gratings customized for a given mission architecture. Both fabricated gratings were tested in the Littrow mounting at the Max-Planck-Institute for extraterrestrial Physics PANTER X-ray test facility to assess their performance. The line spread functions of diffracted orders were measured, and a maximum resolution of 800 $\pm$ 20 is reported. In addition, we also observe evidence of a `blaze' effect from measurements of relative efficiencies of the diffracted orders.