Single-pass synchronized two-color attosecond x-ray free-electron laser featuring attosecond time jitter

Two-color attosecond x-ray pulses are the key to advancing the study of ultrafast dynamics in quantum systems. In this work, we propose a single-pass free-electron laser scheme generating synchronized attosecond two-color x-ray pulses with femtosecond separation and tens-of-gigawatts peak power. By modulating a chirped electron beam with an infrared laser, we create a periodic train of ultrashort current spikes. This scheme utilizes the limited gain bandwidth of the free-electron laser as a filter, allowing only two adjacent current spikes with different resonance wavelengths to lase. This scheme holds promise for delivering sub-300-as two-color x-ray pulses with an intrinsic timing jitter below 100 as. This work provides insights and technical support for generating two-color attosecond x-ray free-electron laser pulses with robust time jitter.