Delivering pulsed and phase stable light to atoms of an optical clock

TL;DR

This paper demonstrates a phase-stable optical link for pulsed laser light in optical clocks, effectively minimizing frequency shifts caused by optical path variations and phase chirps, crucial for improving clock accuracy.

Contribution

It introduces a novel optical path stabilization method for pulsed laser links in optical clocks, achieving sub-2×10⁻¹⁷ frequency shift suppression.

Findings

Achieved phase-stable pulsed light delivery with minimal frequency shift.

Demonstrated effective compensation of optical path length changes.

Enhanced stability for optical clock interrogation.

Abstract

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 challanges 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 acousto optic modulator is below $2\cdot 10^{-17}$.