• Achieving a re-image of the source point within a size of a sub-50 µm level. • The pulse-front tilt can be compensated to sub-femtosecond level (0.9 fs). • The total theoretical throughput can exceed 30% for S-polarized light. • All harmonic light spots can be focused in the same place for easy usability. High-harmonic generation serves as a crucial coherent light source in the extreme ultraviolet to soft X-ray spectral region, featuring ultrashort pulses and broad spectral coverage, with rich applications in ultrafast spectroscopy, nano-imaging, and attosecond science. For certain applications such as angle-resolved photoelectron spectroscopy and coherent diffraction imaging, monochromatic light sources are preferred. The spectral monochromatization process should aim at high optical efficiency and high spectral resolution while maintaining the short pulse characteristics for ultrafast applications. We propose a time-delay compensated monochromator design, employing two off-plane mounted plane gratings to separate and recombine harmonic orders. This configuration achieves both high efficiency (exceeding 30% peak efficiency) and sub-femtosecond pulse-front tilt compensation (average 0.9 fs), thereby preserving the ultrashort temporal characteristics of high-harmonic source. The grating-induced aberrations are corrected by optimizing the toroidal mirror orientations, achieving 50 µm source refocusing within the 20.2-29.4 nm spectral range. Our monochromator design can be extended to other extreme ultraviolet and soft X-ray regions.
Tang et al. (Sun,) studied this question.