title: Modal frequency degeneracy in thermally loaded optical resonators.
abstract: We observe power coupling from the fundamental mode to frequency-degenerate higher-order spatial modes in optical resonators illuminated with a 30 W laser. Thermally-induced modal frequency degeneracy facilitates power transfer from the fundamental mode to higher-order modes, reduces power coupling into the cavity, and triggers power fluctuations. Modeling thermoelastic deformation of a mirror's surface shows predicted modal frequency degeneracy to be in reasonable agreement with experimental observations. Predictions for the Laser Interferometer Gravitational-wave Observatory (LIGO) show that the circulating fundamental-mode power necessary for gravitational-wave detection is compromised at coating absorptions of 3.8 and 0.44 ppm for Enhanced and Advanced LIGO Fabry-Pérot cavities, respectively.
authors.affiliation: E L Ginzton Laboratory, Stanford University, Stanford, CA, USA. abull@stanford.edu
authors.forename: Amber L
authors.initials: AL
authors.lastname: Bullington
authors.forename: Brian T
authors.initials: BT
authors.lastname: Lantz
authors.forename: Martin M
authors.initials: MM
authors.lastname: Fejer
authors.forename: Robert L
authors.initials: RL
authors.lastname: Byer