Simple method for the real-time estimation of timing jitter in ultrashort pulses from mode-locked ultralong ring fiber lasers

A simple method for the estimation of timing jitter in ultrafast lasers is presented and applied for the first time to the characterization of ultralong passively mode-locked femtosecond fiber oscillators with ultra-low repetition rates in the range of kHz. RMS jitter of the order of tens of fs is demonstrated, showing the potential of these recently introduced family of oscillators to be used in phase-noise sensitive applications.