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Digital archive of theses discussed at the University of Pisa


Thesis etd-06212018-133248

Thesis type
Tesi di dottorato di ricerca
Thesis title
Noise from stray light in interferometric gravitational wavedetectors
Academic discipline
Course of study
tutor Fidecaro, Francesco
  • Gravitational waves
  • ray tracing
  • scatter light
  • stray light
  • Virgo
Graduation session start date
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.