Sin Hyuk Yim and colleagues have used two extended-cavity diode lasers, one of them frequency stabilized to a spectroscopic line in rubidium, with the other one phase locked to the first one by means of serrodyne modulation. The sawtooth signal was generated by a nonlinear transmission line where the propagation speed of the electronic signal depends on its amplitude and, hence, results in a steepening of the input signal. The authors demonstrated with the beat note between the two lasers servo bumps close to 10 GHz, indicating a similar bandwidth of the phase-locking loop. From the measured phase noise spectral density, the authors calculated the sensitivity limit for an atom interferometic gravitational acceleration measurement based on their stabilization system. This sensitivity surpassed the conventional locking scheme with the same lasers by about a factor of two, promising the possibility of improved performance in atom interferometric precision measurements.
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