Optical frequency comb-based phase locking of two-color Raman lasers for a magnetically insensitive inertial sensor using a Ba atom interferometer

We aim to realize a quantum inertial sensor with low magnetic sensitivity by constructing an atom interferometer based on the metastable states of barium (Ba) atoms, ultimately leading to the development of an advanced inertial navigation system. Stable phase control between Raman laser pairs is essential for high-contrast atom interferometry. In the magnetically insensitive Ba atom interferometer, the Raman transition between the ³D₁ and ³D₂ states is driven by two lasers at 1108 nm and 1131 nm. Fluctuations in the relative phase between the two lasers deteriorate the interference contrast and result in a degradation of sensitivity, highlighting the need for precise and long-term phase stability. To achieve this, we employ a fiber-based optical frequency comb operating near 1.5 µm, spectrally broadened to 1.1 µm, and phase-lock each Raman laser to different comb modes. This configuration ensures robust control of the two-color relative phase. In this poster, we describe the design and performance of the phase-locking system and report the relationship between the relative phase stability and the observed interference contrast, providing a key technological basis for future Ba-based inertial sensors.