Implementing an electronic sideband offset lock for precision spectroscopy in radium

TL;DR

This paper presents a method for laser frequency stabilization with large offset tunability using an IQ modulator, enabling highly precise isotope shift measurements in radium spectroscopy.

Contribution

The authors demonstrate a novel electronic sideband offset lock technique that achieves at least 6 GHz of offset tunability for laser stabilization, significantly improving precision in isotope shift measurements.

Findings

Achieved at least 6 GHz offset tunability in laser frequency stabilization.

Measured isotope shift between radium isotopes with 0.3 MHz precision.

Enhanced the accuracy of isotope shift data by a factor of 8.

Abstract

We demonstrate laser frequency stabilization with at least 6 GHz of offset tunability using an in-phase/quadrature (IQ) modulator to generate electronic sidebands (ESB) on a titanium sapphire laser at 714 nm and we apply this technique to the precision spectroscopy of $^{226}$Ra, and $^{225}$Ra. By locking the laser to a single resonance of a high finesse optical cavity and adjusting the lock offset, we determine the frequency difference between the magneto-optical trap (MOT) transitions in the two isotopes to be $2630.0\pm0.3$ MHz, a factor of 29 more precise than the previously available data. Using the known value of the hyperfine splitting of the $^{3}P_{1}$ level, we calculate the isotope shift for the $^{1}S_{0}$ to $^{3}P_{1}$ transition to be $2267.0\pm2.2$ MHz, which is a factor of 8 more precise than the best available value. Our technique could be applied to countless other atomic systems to provide unprecedented precision in isotope shift spectroscopy and other relative frequency comparisons.