Laser-frequency stabilization using light shift in compact atomic clocks

This paper describes the light-shift laser-lock (LSLL) technique, an alternative method intended for laser-based compact atomic clocks. The technique greatly simplifies the laser setup by stabilizing the pumping-laser frequency to the same atoms involved in the clock operation, without the need of an external reference. By alternating two clock sequences, the method estimates and cancels out a controlled amount of induced light shift, acting on the laser frequency. The LSLL technique is compatible with state-of-the-art three-level clocks and was demonstrated with field-programmable-gate-array-based electronics on a pulsed-optically-pumped vapor-cell clock developed at INRIM. The results have shown that the LSLL technique operates robustly, having a capture range of gigahertz without significantly compromising clock stability. In our tests, the clock exhibited a white frequency noise of $3.2\times {10}^{-13}{\tau }^{-1/2}$ for averaging times $\tau$ up to 4000 s, reaching a floor below 1×${10}^{-14}$ up to 100 000 s. This level of performance meets the requirements of future global navigation satellite systems on-board clocks, adding the benefits of a reduced clock footprint, as well as increased reliability and robustness.