X-Ray SIG Seminar

X-Ray Science Interest Group

XR SIG about X-Ray SIG Seminar

Location

Virtual

Dates

19 December 2025

Community

XR SIG

Type

Seminar

Advancing Critical-Angle Transmission (CAT) Grating Technology for High Resolving Power Soft X-ray Spectroscopy

Speaker

Ralf Heilmann, MIT

Abstract

High resolving power soft x-ray spectroscopy has been confirmed by the Astro2020 Decadal Survey as a high-priority strategic measurement technique with R = l/Dl up to 7500 for some science cases. Important examples concern feedback across more than fifteen orders of magnitude in length: The characterization of highly ionized gases in galaxy halos and within and around galaxy clusters, accretion onto supermassive black holes, and coronal mass ejections and coronal heating. These science cases can all be uniquely addressed by a high-R soft x-ray grating spectrometer (XGS) instrument downstream of a large-area x-ray mirror, such as the two XGS options for the Lynx mission concept.

I will give an update on the technology underlying the Critical-Angle Transmission (CAT) XGS option and the path toward its goal performance. CAT gratings are freestanding blazed transmission gratings, offering the advantages of low mass, relaxed alignment tolerances, and high resolving power and diffraction efficiency. After many years of lab demonstrations, CAT fabrication is increasingly moving toward volume fabrication using commercial tools from the semiconductor and MEMS industries (addressing manufacturing readiness), in tandem with small-scale demonstrations of improved resolving power and diffraction efficiency (addressing technology readiness). Advanced fast and non-destructive grating bar metrology on 200 mm silicon-on-insulator wafers in combination with machine learning will accelerate fine-tuning of process parameters for key fabrication steps. CAT gratings are also part of the REDSoX soft x-ray polarimetry sounding rocket instrument which is scheduled to fly in 2028.