Low-Drift Zeeman Shifted Atomic Frequency Reference

We present a simple method for producing a low-drift atomic frequency reference based upon the Zeeman effect. Our Zeeman Shifted Atomic Reference 'ZSAR' is demonstrated to have a tens of GHz tuning range, limited only by the strength of the applied field. ZSAR uses Doppler-free laser spectroscopy in a thermal vapor where the vapor is situated in a large, static, and controllable magnetic field. We use a heated Rb-85 vapor cell between a pair of position-adjustable permanent magnets capable of applying magnetic fields up to similar to 1 T. To demonstrate the frequency reference we use a spectral feature from the Zeeman shifted D1 line in Rb-85 at 795 nm to stabilize a laser to the 7S(1/2) -> 23P(1/2) transition in atomic cesium, which is detuned by approximately 19 GHz from the unperturbed Rb transition. We place an upper bound on the stability of the technique by measuring a 2.5 MHz RMS frequency difference between the two spectral features over a 24 hour period. This versatile method could be adapted easily for use with other atomic species and the tuning range readily increased by applying larger magnetic fields. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License.