Asymmetry of Pound-Drever-Hall error signal induced by spatial-mode coherence
Phys. Rev. Applied 24, 014025 – Published 14 July, 2025
DOI: https://doi.org/10.1103/pzrk-wmt3
Abstract
A monotonic stable error signal is essential for the Pound-Drever-Hall (PDH) laser-frequency stabilized system. However, several factors affect the line shape of the error signal even in steady states and the frequency-locked state. Among them, the coherence between the higher-order Gaussian modes and the fundamental modes of the resonate cavity will induce the asymmetry of the PDH error-signal line shape, as well as the zero-crossing-point bias. The effect of the spatial-mode coherence on the error signal is independent of the experimental frequency-scanning process and can still affect the PDH-locking status by changing the locking point of the PDH system. In this paper, we revise the theoretical expression of the PDH error signal according to the theory of coherence between the higher-order modes and the fundamental mode and give the analytical equation of the asymmetry of the PDH error signal. The validation of this theory has been provided by both numerical simulation and experiment.
