Improved efficiency critical-angle transmission gratings for high-resolution soft x-ray spectroscopy

Critical-angle transmission (CAT) gratings are an enabling technology for the Arcus-Probe mission, which addresses high-priority science goals from Astro2020. We previously reported x-ray results from quasi-fully illuminated, co-aligned CAT gratings showing record-high resolving power R = lambda/Delta lambda up to 1.3x10^4 in 18th and 21st orders at Al-K, and diffraction efficiency of blazed orders in agreement with pencil beam synchrotron measurements and model predictions at O-K. We will give updates on enhanced diffraction efficiency for CAT gratings that were chemically thinned after fabrication.