Single and coupled cavity mode sensing schemes using a diagnostic field

Aaron W. Goodwin-Jones, Haochen Zhu, Carl Blair, Daniel D. Brown, Joris van Heijningen, Li Ju, Chunnong Zhao

Research output: Contribution to journalArticlepeer-review


Precise optical mode matching is of critical importance in experiments using squeezed-vacuum states. Automatic spatial-mode matching schemes have the potential to reduce losses and improve loss stability. However, in quantum-enhanced coupled-cavity experiments, such as gravitational-wave detectors, one must also ensure that the sub-cavities are also mode matched. We propose what we believe to be a new mode sensing scheme, which works for simple and coupled cavities. The scheme requires no moving parts, nor tuning of Gouy phases. Instead a diagnostic field tuned to the HG20/LG10 mode frequency is used. The error signals are derived to be proportional to the difference in waist position, and difference in Rayleigh ranges, between the sub-cavity eigenmodes. The two error signals are separable by 90 degrees of demodulation phase. We demonstrate reasonable error signals for a simplified Einstein Telescope optical design. This work will facilitate routine use of extremely high levels of squeezing in current and future gravitational-wave detectors.

Original languageEnglish
Pages (from-to)35068-35085
Number of pages18
JournalOptics Express
Issue number21
Publication statusPublished - 9 Oct 2023

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