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 <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><a:mn>3.2</a:mn><a:mo>×</a:mo><a:msup><a:mn>10</a:mn><a:mrow><a:mo>−</a:mo><a:mn>13</a:mn></a:mrow></a:msup><a:msup><a:mi>τ</a:mi><a:mrow><a:mo>−</a:mo><a:mn>1</a:mn><a:mo>/</a:mo><a:mn>2</a:mn></a:mrow></a:msup></a:math> for averaging times <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><d:mi>τ</d:mi></d:math> up to 4000 s, reaching a floor below 1×<g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><g:msup><g:mn>10</g:mn><g:mrow><g:mo>−</g:mo><g:mn>14</g:mn></g:mrow></g:msup></g:math> 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. Published by the American Physical Society 2024