Simultaneous two-photon resonant optical laser locking (STROLLing) in the hyperfine Paschen--Back regime

TL;DR

This paper introduces a technique for simultaneously locking two lasers to a two-photon transition in rubidium atoms under a strong magnetic field, achieving long-term stability and low frequency instability.

Contribution

We develop and demonstrate a method to lock two lasers simultaneously in the hyperfine Paschen-Back regime, maintaining stability over 24 hours with minimal frequency drift.

Findings

Locking duration exceeds 24 hours

Frequency instability is less than 6 MHz

Effective in hyperfine Paschen-Back regime

Abstract

We demonstrate a technique to lock simultaneously two laser frequencies to each step of a two-photon transition in the presence of a magnetic field sufficiently large to gain access to the hyperfine Paschen-Back regime. A ladder configuration with the 5S$_{1/2}$, 5P$_{3/2}$ and 5D$_{5/2}$ terms in a thermal vapour of $^{87}$Rb atoms is used. The two lasers remain locked for more than 24 hours. For the sum of the laser frequencies, which represents the stability of the two-photon lock, we measure a frequency instability of less than the Rb D$_2$ natural linewidth of 6 MHz for nearly all measured time scales