Abstracts Astronomy & Space Science

Detector Improvements and Optimization to Advance Gravitational-wave Astronomy

by Varun Srivastava

The thesis covers a range of topics relevant to the current and future gravitational-wave facilities. After the last science observing run, O3, that ended in March 2020, the aLIGO and VIRGO gravitational-wave detectors are undergoing upgrades to improve their sensitivity. My thesis focuses on the work done at the LIGO Hanford Observatory to facilitate these upgrade activities. I worked to develop two novel technologies with applications to gravitational-wave detectors. First, I developed a high-bandwidth, low-noise, flexure-based piezo-deformable mirror for active mode-matching. Mode-matching losses limit improvements from squeezing as they distort the ground state of the squeezed beam. For broadband sensitivity improvements from frequency-dependent squeezing, it is critical to ensure low mode-mismatch losses. These piezo-deformable mirrors are being installed at the aLIGO facilities. Second, I worked to develop and test a high-resolution wavefront sensor that employs a time-of-flight sensor. By achieving phase-locking between the demodulation signal for the time-of-flight sensor and the incident modulated laser beam, this camera is capable of sensing higher-order mode distortions of the incident beam. Cosmic Explorer is a proposed next-generation gravitational-wave observatory in the United States that is planned to be operational by the mid-2030s. Cosmic Explorer along with Einstein Telescope will form a network of next-generation gravitational-wave detectors. I propose the science-goal-focused tunable design of the Cosmic Explorer detectors that allow for the possibility to tune with sensitivity at low, mid, and high frequencies. These tuning options give Cosmic Explorer the flexibility to target a diverse set of science goals with the same detector infrastructure. The technological challenges to achieving these tunable configurations are presented. I find that a 40 km Cosmic Explorer detector outperforms a 20 km in all key science goals other than access to post-merger physics. This suggests that Cosmic Explorer should include at least one 40 km facility. I also explore the detection prospects of core-collapse supernovae with the third-generation facilities – Cosmic Explorer and Einstein Telescope. I find that the weak gravitational-wave signature from core-collapse supernovae limits the likely sources within our galaxy. This corresponds to a low event rate of two per century.