Influence of a magnetic field on the frequency of a laser stabilized to molecular iodine

TL;DR

This study investigates how weak magnetic fields influence the frequency stability of a laser stabilized to molecular iodine, demonstrating the importance of magnetic shielding for optimal performance.

Contribution

It provides the first measurement of the linear Zeeman shift on a specific iodine hyperfine transition used for laser frequency stabilization.

Findings

Magnetic shielding improves short-term frequency stability.

Zeeman effect causes measurable frequency shifts in iodine hyperfine lines.

Uncontrolled magnetic fields can limit laser frequency stability to above 10^{-14}.

Abstract

We report on the effect of a weak magnetic field applied on an iodine cell used to frequency stabilize a laser. A 1.5$~\mu$m laser is frequency tripled in order to excite the molecular transitions at 0.51$~\mu$m and frequency locked on a hyperfine line. With this frequency reference, we report short-term stability about $3\,\times\,10^{-14}~\tau^{-1/2}$, with a minimum value of $4\,\times\,10^{-15}$ at 200~s. The lower part of $10^{-15}$ frequency stability domain is reached, in our case, only by adding an efficient magnetic shield around the sealed quartz iodine cell. In order to quantify the Zeeman effect, we applied magnetic fields of several $\,\times\,10^{-4}$~T on the cell containing the iodine vapour. The Zeeman effect affects the lineshape transition in such a way that we observe a modification of the laser frequency. We have measured this linear Zeeman shift at $(1062\pm6)\,\times\,10^{4}$~Hz/T for the $a1$ hyperfine component of the R(34)~44-0 transition, near 514~nm by applying a magnetic field along the cell. Thus, in case of uncontrolled magnetic fields of an order of magnitude of 1$\,\times\,10^{-4}$~T, the frequency stability is limited in the upper of the $10^{-14}$ domain.