Backscattered light noise and polarisation fluctuations in the Virgo interferometer (20' + 10'Q/A) Room: Auditorium Marcel Vivargent Gravitational wave detection is carried out using the LIGO-Virgo-KAGRA detectors, systems that are sensitive enough to measure distances *one hundred thousand time* smaller than the size of a proton. This sensitivity is achieved by reducing several sources of noise, including backscattered light. This thesis is divided into two parts, and this presentation will focus on the work carried out on backscattered light noise. More specifically, it will focus on the analysis of measurements using a backscattermeter, the analysis of experiments on Virgo and the construction of a simulation to produce these results.