Arm locking for laser interferometer space antenna

The Laser Interferometer Space Antenna (LISA) is a collaborative National Aeronautics and Space Administration (NASA)/European Space Agency (ESA) space mission to detect gravitational waves in the frequency region of 3 × 10-5 Hz to 1 Hz by means of laser interferometry. It will be the first space-based interferometric gravitational wave detector to be launched in 2020s. LISA will consist of three identical spacecraft arranged in a quasi-equilateral triangular constellation with 5 Gm on each side. Each spacecraft houses two drag-free proof masses that follow the geodesic motion. The Interferometric Measurement System (IMS) of LISA monitors changes in the proper distance between two proof masses on each respective spacecraft.;Laser frequency stabilization is one of the most significant and difficult issues for the IMS of LISA. Arm locking as a proposed frequency stabilization technique, transfers the stability of the long arm lengths to the laser frequency. The arm locking sensor synthesizes an adequately filtered linear combination of the inter-spacecraft phase measurements to estimate the laser frequency noise, which can be used to control the laser frequency. Due to the large propagation delay during the light transmission, the arm locking controller needs to be carefully designed to retain enough phase margin. A potential problem for arm locking is that the Doppler shift of the return beam will cause a constant pulling in the master laser frequency if unaccounted for in the phase measurement. Until now all the benchtop experiments on arm locking verified only the basic single arm locking configuration with unrealistic short delay time and without any Doppler estimation error at the phasemeter. At the University of Florida we developed the hardware-based University of Florida LISA Interferometer Simulator (UFLIS) to study and verify laser frequency noise reduction and suppression techniques under realistic LISA-like conditions. These conditions include the variable Doppler shifts between the spacecraft, LISA-like signal travel times, far-end heterodyne phase-locking, realistic laser frequency and timing noise. In this dissertation we will systematically introduce the cutting edge of experimental studies of arm locking under these realistic conditions. We have built an analog/digital hybrid system to demonstrate the control system of various arm locking schemes and their incorporation with pre-stabilization subsystems. We measured the noise suppression in our experiments as well as the frequency pulling in the presence of Doppler frequency error. With the achievement of meeting the requirement, our pioneering work have sufficiently demonstrated the validity and feasibility of arm locking under LISA-like conditions.