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Description
Future upgrades and detectors aim to both reduce quantum noise by 10 dB and to increase the circulating power in the interferometer arm cavities. Achieving these goals will be extremely challenging due, in part, to the degradations to the squeezed state caused by mode mismatch between the internal interferometer optical cavities and between the auxiliary external cavities. There are two types of internal mismatch which are mainly due to the thermal aberrations generated when the test mass optics absorb a small fraction of the circulating arm power. The two types of mismatch are predominantly responsible for different squeezing degradations since the dynamics responsible for the degradations caused by the mismatch between the quadratic part of the wavefront of two modes has a low-pass frequency dependence while the dynamics of the mismatch due to all higher order thermal aberrations has a high-pass behavior. These dynamics can be measured with an audio diagnostic field injected along the squeeze path, and efforts are underway in the current detectors and in a laboratory setting to use such measurements to characterize the squeezing degradations and correct them with thermal actuators.