Frequency stabilization of a 650 nm laser to I$_{2}$ spectrum for trapped $^{138}$Ba$^{+}$ ions

TL;DR

This paper demonstrates a novel frequency stabilization method for a 650 nm laser using iodine spectral lines, enabling precise control for Ba$^{+}$ ion experiments, which was previously unreported.

Contribution

The authors develop and validate a new stabilization scheme for a 650 nm laser using iodine lines, facilitating improved manipulation of Ba$^{+}$ ions.

Findings

Identified 20 iodine spectral lines near the Ba$^{+}$ transition.

Achieved laser stabilization with a 350 MHz offset from resonance.

Confirmed frequency differences align with theoretical predictions.

Abstract

The optical manipulation of Ba$^{+}$ ions is mainly performed by a 493 nm laser for the S$_{1/2}$-P$_{1/2}$ transition and a 650 nm laser for the P$_{1/2}$-D$_{3/2}$ transition. Since the branching ratio between the 493 nm and 650 nm transitions of a single Ba$^{+}$ ion is comparable, stabilization systems of both lasers are equally important for Doppler cooling, sub-Doppler cooling, optical pumping and state detection. The stabilization system of a 493 nm laser to an absolute Te$_2$ reference has been well established. However, the stabilization of a 650 nm laser has not been presented before. Here we report twenty spectral lines of I$_{2}$ in the range of 0.9 GHz above the resonance of the P$_{1/2}$-D$_{3/2}$ transition. We stabilize the 650 nm laser through the optical cavity to the lowest one among these lines, which is about 350 MHz apart, as the absolute frequency reference. Furthermore, we measure the frequency differences between these iodine lines and the Ba$^+$ resonance through fluorescence excitation spectrum with well-resolved dark states, which is in agreement with the theoretical expectation. The presented stabilization scheme enables us to perform precise experiments with Ba$^{+}$ ions.