A transmission grating extreme ultraviolet spectrometer using a gradient-reflectivity Al/Zr multilayer mirror for the range of 24–32 nm

Compact extreme ultraviolet (EUV) spectrometers are increasingly required for laboratory plasma diagnostics and EUV optical metrology, where broadband coverage and high spectral resolution must be simultaneously achieved. In this paper, a compact spectrometer operating in the 24-32 nm band is presented, enabled by a near-normal-incidence spherical mirror coated with an aperiodic Al(1.5%Si)/Zr multilayer specifically designed to exhibit a monotonic, gradient-reflectivity profile. The multilayer was optimized using interactive multilayer design to provide a broadband response with a reflectance increasing from ∼5% to ∼20% toward the long-wavelength end, thereby compensating for the intrinsic efficiency roll-off of the other optical elements in this band. Synchrotron measurements confirm that the fabricated coating closely reproduces the designed peak position, bandwidth, and gradient behavior of reflectivity. With this system, single-shot laser-produced plasma EUV emission from high-purity W, Mo, Fe, Cu, Cr, Si, and Al targets was systematically characterized, revealing the optimal excitation power density and multi-shot lifetime behavior for each material within this spectral range. Overall, this spectrometer achieves a spatial resolution of ∼31 μm and maintains a spectral resolution better than 0.2 nm across the full 24-32 nm band, establishing a compact and high-performance solution for broadband EUV source diagnostics.