Characterization of the Alignment Sensing and Control Subsystem of Advanced LIGO
With a strain sensitivity of 10−23/√Hz achieved by the detectors, LIGO made the first direct observation of gravitational waves on September 14, 2015. Dozen of events have been observed since then, which include massive black hole mergers, binary neutron star mergers and BH and neutron stars. The next step is to upgrade the detector, such that we can be able to achieve a binary neutron star inspiral range (BNS) > 120 Mpc. One of the main detector upgrades after the second observing run O2, in addition to the installation of an in-vacuum squeezer and the replacement of the core optics, was increase in laser power input to at least 50W; two times the power used for the second observational run (O2). Since the power build up inside the interferometer's cavities creates radiation pressure torque, increasing the power enlarges the angular motion of the main optics which could induce potential instabilities. As the system changes, our angular sensing might change too. An efficient angular control system to keep the mirrors aligned and the interferometer locked is therefore needed. This thesis present different studies and analyses performed to characterize the Alignment Sensing and Control sub-system that were done during the observing run O2, and towards the third observing run (O3). All the work discussed in this document was done while working with the commissioning team at the LIGO Livingston Observatory (LLO) as a LIGO fellow.