Noise from stray light in interferometric gravitational wavedetectors

The era of the second generation of gravitational waves detectors has been very successful with the advanced versions of Virgo and LIGO. In September 2015, LIGO had detected the first gravitational wave the day before it started the first science run. After a successful first science run, LIGO upgraded both interferometers to improve the sensitivity and during the second science run Virgo joined LIGO in the search for gravitational waves. Many challenges have been faced in order to improve on the sensitivity of advanced detectors. One of those challenges has been stray light. Up to now, both Virgo and LIGO have been affected by stray light problems and this is expected to be an important problem to address in the future third generation of gravitational wave detectors. At the same time, the search for stray light is probably the least studied aspect before the instrument is switched on. For this reason, it is important to develop new methods to predict and deal with stay light. This thesis focuses on the study and simulation of light in order to find the coupling between stray light and vibration of mechanical elements that spoil the sensitivity during operation. The first section contains a short summary of the state of the art of gravitational waves detectors. The first chapter presents the General Relativity principle to generate gravitational waves and summarises the astrophysical sources that emit gravitational waves, either they have already been detected or not. The second section presents the computational methods used and developed to simulate stray light. The third chapter explains ray tracing as a tool to simulate stray light without frequency dependence. The fourth chapter contains two diferent extensions to ray tracing. The first is the development done to implement the coupling between mechanical elements and stray light. The second part describes different tests to accelerate the code using GPU and its results. The third part is focused on the results. The fith chapter contains simulations of stray light with the methods presented in the second part. Finally, the sixth chapter presents the studies done to analysing stray light in Virgo during the period of commissioning.