Opportunities and challenges of X-ray multilayer mirror coatings for NewAthena and Future High-Energy Missions

High-energy astrophysics missions demand cutting-edge technologies to assure their maximum observational capabilities. This study explores multilayer coatings for X-ray mirrors, specifically assessing their potential applications for the NewAthena mission and other possible future high-energy missions. Our work emphasizes the design parameters crucial for enhancing mirror performance and investigates the experimental challenges related to the fabrication and performance evaluation of multilayer coatings. We present various concept designs for both soft and hard X-ray focusing telescopes, incorporating simple single-layer and bilayer coatings, with a particular focus on linear and depth-graded multilayer coatings. Leveraging state-of-the-art understanding and modeling of relevant effects influencing telescope performance enables a realistic extension of coating designs to higher energies. The implications of our findings not only endorse the use of multilayer coatings for the NewAthena mission but also offer insights into the broader landscape of future high-energy astrophysics missions.