High-resolution, high-efficiency narrowband spectroscopy with an s-p-phased holographic grating in double passC. Farret Jentink, F. Pepe, C. Lovis, C. Schwab, F. Wildi and A. ClawsonA&A, 698 (2025) A249DOI: https://doi.org/10.1051/0004-6361/202554218