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arXiv · 2512.03900

Errors in PDH offset locking due to spurious spectral features

Roame A. Hildebrand·Wance Wang·Connor Goham·Alessandro Restelli·Joseph W. Britton
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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.

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Roame A. Hildebrand, Wance Wang, Connor Goham, Alessandro Restelli, Joseph W. Britton. 2025-12-03. Errors in PDH offset locking due to spurious spectral features. https://doi.org/10.1364/oe.572595

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