Laser Frequency Stabilization Using Light Shift in Compact Atomic Clocks

TL;DR

This paper introduces the Light-Shift Laser-Lock (LSLL) technique for compact atomic clocks, which stabilizes laser frequency by canceling light shifts, leading to robust, high-stability clocks suitable for GNSS applications.

Contribution

The paper presents a novel LSLL method that simplifies laser stabilization in compact atomic clocks without external references, demonstrating robustness and high stability.

Findings

Operates with a gigahertz capture range

Achieves a white frequency noise of 3.2×10⁻¹³ τ⁻¹/²

Maintains stability below 1×10⁻¹⁴ up to 100,000 seconds

Abstract

This paper describes the Light-Shift Laser-Lock (LSLL) technique, a novel method intended for compact atomic clocks that greatly simplifies the laser setup by stabilizing the pumping-laser frequency to the atoms involved in the clock, without the need of an external reference. By alternating two clock sequences with different light shifts, 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 3-level clocks and was demonstrated with FPGA-based electronics on a pulsed-optically-pumped (POP) 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 time up to 4000 s, reaching a floor below $1 \times 10^{-14}$ up to 100 000 s. These performance levels meet the requirements of future Global Navigation Satellite Systems (GNSS) on-board clocks, and offer the added benefits of a reduced clock footprint, as well as increased reliability and robustness.