Optical flywheels with attosecond jitter

It has been known for some time that the steady-state pulse propagating inside a mode-locked laser is the optical equivalent of a mechanical flywheel. By measuring the timing error spectrum between phase-locked optical pulse trains emitted from two nearly identical 10 fs Ti:sapphire lasers, we demonstrate a record low integrated timing error of less than 13 as, measured from d.c. to the Nyquist frequency of the pulse train, which is 41 MHz. This corresponds to the lowest high-frequency phase noise ever recorded of -203 dBc Hz(-1) (assuming a 10 GHz carrier) for offset frequencies greater than 1 MHz. Such a highly uniform train of pulses will enable the synchronization of pump-probe experiments that measure the evolution dynamics of chemical(1,2) and atomic processes(3,4) evolving on femtosecond and attosecond timescales. The ultralow timing jitter of such pulse trains will also allow photonic analog-to-digital conversion of mid-infrared waveforms with a resolution of 6 bits(5).