AttoSHINE: Generation of Continuous-Wave Terawatt-Scale Attosecond X-Ray Pulses at SHINE

Attosecond x-ray pulses are a critical tool for tracking ultrafast electron dynamics in condensed matter, molecular systems, and strongly correlated materials. Recent breakthroughs have pushed x-ray free-electron lasers (XFELs) into the attosecond domain, substantially surpassing their previous femtosecond capabilities. Building on these advancements, this work investigates the potential of the Shanghai HIgh repetitioN rate XFEL and Extreme light facility (SHINE), China’s first continuous-wave (CW) XFEL, to generate intense attosecond x-ray pulses, thereby offering transformative capabilities for x-ray science. Through comprehensive start-to-end simulations, we show that SHINE is capable of producing terawatt-scale pulses at both soft and hard x-ray ranges. This is achieved using a self-chirping scheme within the existing machine configuration, requiring no additional hardware. We further find that superradiant behavior in the postsaturation regime plays a central role in attosecond XFEL, enabling higher peak power and shorter attosecond pulses. Our results illustrate the wide applicability of the self-chirping scheme and demonstrate that CW XFELs can generate intense attosecond x-ray pulses at megahertz repetition rates, opening new opportunities for real-time studies of electronic dynamics in complex systems.