Optical frequency stabilization with a synchronous frequency-to-voltage converter

Between a frequency comb mode and a continuous-wave (cw) laser, we demonstrate that a frequency-to-voltage converter can be used to transfer frequency instability in the 10^-14 range for integration times τ between 0.25 and 2100 s. The technique is relevant when the optical beat between laser signals is weak and a high level of frequency stability is required both in the short term and long term, as in the case of laser cooling with very narrow transitions. The impressive stability transfer arises through the use of a synchronous voltage-to-frequency converter that relies on an external CMOS oscillator. Aided by an atomic reference to the frequency comb, the method grants long-term stability to the cw laser, superior to that achieved with most optical cavities.