DC response of an interferometer topology with an L-shaped cavity: a tabletop study

TL;DR

This study experimentally investigates a novel L-shaped cavity interferometer topology for gravitational-wave detection, revealing its optical response characteristics and confirming theoretical predictions, which aids in understanding its lock acquisition process.

Contribution

The paper provides the first tabletop experimental characterization of the DC response of an L-shaped cavity interferometer topology with a Sagnac vortex, confirming theoretical models.

Findings

The cavity input coupler becomes transparent at resonance, simplifying the response.

The Sagnac vortex splits into two independent paths, acting as separate pumping routes.

Experimental results agree with theoretical predictions.

Abstract

A new interferometer topology for kilohertz gravitational-wave detection was recently proposed in [Zhang et al. Phys. Rev. X 13, 021019 (2023)]. The design is based on an L-shaped optical cavity pumped through a Sagnac-like vortex. We report a tabletop experiment that characterizes the interferometer's optical response near DC. When the laser frequency is locked to the resonance of the L-shaped cavity, we observe that the cavity input coupler becomes effectively transparent, yielding a simple Michelson-like response. Moreover, the Sagnac vortex separates into upper and lower paths, which behave as two independent pumping paths driving the cavity. These observations are in agreement with theoretical predictions. Our results provide an intuitive physical picture of this interferometer topology and offer insight into its lock acquisition strategy.