Precise mode matching is needed to maximize performance in coupled cavity interferometers such as Advanced LIGO. In this paper we present a new mode matching sensing scheme that uses a single radio frequency higher order mode sideband and single element photodiodes. It is first order insensitive to misalignment and can serve as an error signal in a closed loop control system for a set of mode matching actuators. We also discuss how it may be implemented in Advanced LIGO. The proposed mode matching error signal has been successfully demonstrated on a tabletop experiment, where the error signal increased the mode matching of a beam to a cavity to 99.9%.
@article{arxiv.2008.05839,
title = {Mode matching error signals using radio-frequency beam shape modulation},
author = {Alexei A. Ciobanu and Daniel David Brown and Peter J. Veitch and David J. Ottaway},
journal= {arXiv preprint arXiv:2008.05839},
year = {2020}
}