Errors in PDH offset locking due to spurious spectral features
Abstract
The Pound-Drever-Hall (PDH) technique is widely used to stabilize the frequency of lasers. Here we report on a routinely underestimated source of error in PDH offset-locking: a shift in the lock point due to the unintended interaction between residual optical sidebands and higher-order spatial modes in misaligned Fabry-Perot cavities. Significant frequency deviations-up to 50% of the cavity linewidth-can arise when the optical offset is obtained from a sinusoidally driven EOM. We measure this deviation experimentally, find agreement with a simple model, and show how a spectrally-pure frequency offset can reduce the deviation by an order of magnitude. Our findings draw attention to a systematic effect of importance to precision optical spectroscopy, optical clocks, and quantum information science.
Cite
@article{arxiv.2512.03900,
title = {Errors in PDH offset locking due to spurious spectral features},
author = {Roame A. Hildebrand and Wance Wang and Connor Goham and Alessandro Restelli and Joseph W. Britton},
journal= {arXiv preprint arXiv:2512.03900},
year = {2025}
}