Delivering pulsed and phase stable light to atoms of an optical clock
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In optical clocks, transitions of ions or neutral atoms are interrogated using pulsed ultra-narrow laser fields. Systematic phase chirps of the laser or changes of the optical path length during the measurement cause a shift of the frequency seen by the interrogated atoms. While the stabilization of cw-optical links is now a well-established technique even on long distances, phase stable links for pulsed light pose additional challenges and have not been demonstrated so far. In addition to possible temperature or pressure drift of the laboratory, which may lead to a Doppler shift by steadily changing the optical path length, the pulsing of the clock laser light calls for short settling times of stabilization locks. Our optical path length stabilization uses retro-reflected light from a mirror that is fixed with respect to the interrogated atoms and synthetic signals during the dark time. Length changes and frequency chirps are compensated for by the switching AOM. For our strontium optical lattice clock, we have ensured that the shift introduced by the fiber link including the pulsing acoustooptic modulator is below 2×10-17.
KeywordsOptical Path Length Voltage Control Oscillator Frequency Comb Clock Pulse Beat Signal
The support by the Centre of Quantum Engineering and Space-Time Research (QUEST), funding from the European Community’s ERA-NET-Plus Programme (Grant No. 217257), from the European Community’s Seventh Framework Programme (Grant No. 263500), and by the ESA and DLR in the project Space Optical Clocks is gratefully acknowledged. We thank Burghard Lipphardt for helpful discussions.
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