Precision interferometry in a new shape: higher-order Laguerre-Gauss modes for gravitational wave detection

Abstract

The sensitivity of the next generation of interferometric gravitational wave detectors will be limited in part by thermal noises of the optics. It has been proposed that using higher-order Laguerre-Gauss (LG) beams in the interferometers can reduce this noise. This thesis documents progress made in assessing the compatibility of higher-order LG beam technology with the existing precision interferometry framework used in the gravitational wave detector community. A numerical investigation was made into techniques for generating higher-order LG modes with a phase modulating surface. The optimal conditions for mode conversion were determined using fast Fourier transform (FFT) simulations, and predictions were made for the mode purity achievable with this method. Table-top experiments performed at Birmingham demonstrated the generation of higher-order LG modes using a spatial light modulator, and showed for the first time the feedback control of an optical cavity on resonance for higher-order LG modes. An increase in the purity of LG\(_{33}\) modes from 51% to over 99% upon transmission through the cavity was shown. Investigations were carried out at the Glasgow 10m prototype detector into the performance of the LG\(_{33}\) mode in a suspended 10m cavity, providing useful insights into the compatibility of LG modes with larger scale interferometers.