10-fs-level synchronization of femtosecond laser with RF master oscillator

Laser-to-RF synchronization plays a crucial role in various scientific and technological domains. It is instrumental in generating high-quality electron beams, producing high-performance FEL pulses, ex-ploring ultrafast dynamical processes, and achieving precise measurements and transmission. Passively mode-locked femtosecond lasers are known for their exceptionally low noise characteristics, particularly in the high-offset frequency range, where jitter remains less than 5 fs from 1 kHz to 1 MHz. Meanwhile, RF master oscillators provide outstanding long-term sta-bility in the offset frequency range. This paper demon-strates that integrating the low-noise performance of passively mode-locked femtosecond laser with the superior stability of RF master oscillator enables the achievement of 10-fs-level synchronization. By im-plementing an RF-based phase-locked loop (PLL) scheme, we achieved an absolute timing jitter of 17.4 fs integrated from 10 Hz to 1 MHz.