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Free keywords:
Astrophysics, Instrumentation and Methods for Astrophysics, astro-ph.IM, Physics, Instrumentation and Detectors, physics.ins-det
Abstract:
Gravitational waves have revolutionised the field of astronomy by providing
scientists with a new way to observe the universe and gain a better
understanding of exotic objects like black holes. Several large-scale laser
interferometric gravitational wave detectors (GWDs) have been constructed
worldwide, with a focus on achieving the best sensitivity possible. However, in
order for a detector to operate at its intended sensitivity, its optics must be
free from imperfections such as thermal lensing effects. In the GEO\,600
gravitational wave detector, the beam splitter (BS) experiences a significant
thermal lensing effect due to the high power build-up in the Power Recycling
Cavity (PRC) combined with a very small beam waist. This causes the fundamental
mode to be converted into higher order modes (HOMs), subsequently impacting the
detector's performance. To address this issue, the GEO\,600 detector is
equipped with a thermal compensation system (TCS) applied to the BS. This
involves projecting a spatially tunable heating pattern through an optical
system onto the beam splitter. The main objective of the TCS is to counteract
the thermal lens at the BS and restore the detector to its ideal operating
condition. This paper presents the new beam splitter TCS in GEO\,600, its
commissioning, and its effect on strain sensitivity. It also outlines the
planned upgrade to further enhance the performance of the TCS.
