Systematic investigation of the diffraction efficiency of sub-15 nm resolution soft X-ray zone plates via simulation and measurement.

Soft X-ray Fresnel zone plates (FZPs) are core components in synchrotron radiation microscopy systems, and their diffraction efficiency directly determines focal intensity and imaging performance. Currently, research on 15 nm high-resolution FZPs has been primarily focused on spatial resolution, while experimental investigations into their diffraction efficiency remain scarce. Moreover, inconsistencies observed among different measurement approaches significantly hinder the accurate evaluation of their optical performance. In this study, we conducted systematic comparative measurements of the relative and absolute diffraction efficiencies of an FZP with a 12.5 nm outermost zone width. By integrating the beamline's active closed-loop vibration suppression and high-speed real-time incident flux normalization, we effectively mitigated environmental noise and top-up injection fluctuations. This specific setup enabled highly repeatable efficiency measurements over the short continuous measurement period at the 15 nm resolution limit, yielding a relative RMS fluctuation below 3%. These measurement results were subsequently benchmarked against a whole-aperture, area-averaged rigorous coupled-wave analysis model. Results indicate that relative diffraction efficiency aligns well with the theoretical calculations, supporting the overall consistency between the measured and calculated energy responses. Conversely, absolute diffraction efficiency more directly quantifies the realized first-order energy conversion under the present synchrotron conditions by accounting for practical factors, including membrane transmission loss, alignment errors, and incident intensity fluctuations. This precise characterization and systematic analysis of the FZP with a 12.5 nm outermost zone width provide a useful reference for evaluating high-resolution optics and support the optimized design and standardized development of next-generation synchrotron beamlines.