Sider, A. et al. (2023) E-TEST: a compact low-frequency isolator for a large cryogenic mirror. Classical and Quantum Gravity, 40(16), 165002. (doi: 10.1088/1361-6382/ace230) Text 364816.pdf - Published Version Available under License Creative Commons Attribution. 3MB Abstract To achieve the expected level of sensitivity of third-generation gravitationalwave (GW) observatories, more accurate and sensitive instruments than those of the second generation must be used to reduce all sources of noises.