Upgrades and improvements of ground-basedlaser interferometric gravitational wave detectors

Gravitational wave astronomy has rapidly developed into a powerful means of probing compact objects and understanding the evolution of the Universe. In order to improve sensitivity and expand the detection band, ground-based laser interferometers such as LIGO, Virgo, and KAGRA are constantly upgraded. This review summarizes their systematic development with an emphasis on noise sources and mitigation strategies. After outlining the principle of gravitational wave detection with laser interferometry, we analyze dominant noise sources, including quantum vacuum fluctuations, thermal noise, and seismic disturbances, and introduce techniques such as frequency-dependent squeezed light, advanced seismic isolation, multi-stage suspensions, and cryogenic mirrors. For LIGO, we highlight the transition from the Initial to Advanced configurations, which results in strain sensitivities of the order of <inline-formula><tex-math id="M1">\begin{document}$10^{-24}/\sqrt{\text{Hz}}$\end{document}</tex-math></inline-formula> and leads directly to the first detection, GW150914, and over one hundred subsequent events during O1 to O4. The unique superattenuator system of Virgo and its recent implementation of squeezed light, as well as the underground design of KAGRA and the use of cryogenic sapphire test masses, represent different approaches to suppressing low-frequency and thermal noise. In addition, we compare the technical routes adopted by different detectors and summarize the lessons learned from their upgrades, thereby providing valuable guidance for designing future detectors. Finally, we present next-generation projects, including LIGO Voyager, the Cosmic Explorer, and the Einstein Telescope, which aim to increase sensitivity by up to orders of magnitude and provide new research opportunities for developing gravitational-wave cosmology and fundamental physics. Overall, the development of detector technologies has been a key driving force for advances in gravitational wave astronomy, and the forthcoming facilities will change our ability to explore the universe.