Design and control of femtosecond lasers for optical clocks and the synthesis of low-noise optical and microwave signals

This paper describes recent advances in the design and control of femtosecond laser combs for their use in optical clocks and in the synthesis of low-noise microwave and optical signals. The authors present a compact and technically simple femtosecond laser that directly emits a broad continuum and shows that it can operate continuously on the timescale of days as the phase-coherent "clockwork" of an optical clock. They further demonstrate phase locking of an octave-spanning frequency comb to an optical frequency standard at the millihertz level. As verified through heterodyne measurements with an independent optical frequency standard, this provides a network of narrow optical modes with linewidths at the level of ≤150 Hz, presently limited by measurement noise. Finally, they summarize their progress in using the femtosecond laser comb to transfer the stability and low phase-noise optical oscillators to the microwave domain.