Experimental Demonstrations of Alignment and Mode Matching in Optical Cavities with Higher-Order Hermite-Gauss Modes

Higher -order spatial laser modes have recently been investigated as candidates for reducing test -mass thermal noise in ground -based gravitational -wave detectors such as advanced LIGO. In particular, higherorder Hermite-Gauss (HG) modes have gained attention within the community for their more robust behaviors against random test -mass surface deformations and stronger sensing and control capacities. In this Letter we offer experimental investigations on various aspects of HG mode interferometry. We have generated purified HG modes up to the twelfth order HG6,6 mode, with a power conversion efficiency of 38.8% and 27.7% for the HG3,3 and HG6,6 modes respectively. We demonstrate for the first time the misalignment and mode mismatch -induced power coupling loss measurements for HG modes up to the HG6,6. We report an excellent agreement with the extended numerical power loss factors that in the "small power loss" region converge to 2n + 1 or n2 + n + 1 for a misaligned or mode mismatched HGn,n mode. We also demonstrate the wavefront sensing (WFS) signal measurement for HG modes up to the HG6,6. The measurement result is accurately in accordance with theoretical WFS gain beta n,n-1 HGn,n mode, with beta n,n-1 being the beat coefficient of the adjacent HGn,n and HGn-1,n modes on a split photodetector. p + beta n,n+1 ffiffin pfor an ffiffiffiffiffiffiffiffiffiffin + 1