Point absorbers in Advanced LIGO.

Small, highly absorbing points are randomly present on the surfaces of the main interferometer optics in Advanced LIGO. The resulting nanometer scale thermo-elastic deformations and substrate lenses from these micron-scale absorbers significantly reduce the sensitivity of the interferometer directly though a reduction in the power-recycling gain and indirect interactions with the feedback control system. We review the expected surface deformation from point absorbers and provide a pedagogical description of the impact on power buildup in second generation gravitational wave detectors (dual-recycled Fabry-Perot Michelson interferometers).

Narrow-linewidth fiber amplifier for gravitational-wave detectors.

We report on the design and noise performance of a narrow-linewidth Yb-doped fiber amplifier emitting up to 178 W at 1064 nm for possible use in gravitational-wave (GW) interferometric detectors. The novel design utilizes a specialty large-mode-area gain fiber with confined-core doping and depressed cladding, followed by a smaller-core passive fiber to improve output beam quality. We show that the free-running noise of the system is equal to or better than current Advanced LIGO noise requirements.

Simple method for locking birefringent resonators.

We report on a simple method of locking a laser to a birefringent cavity using polarization spectroscopy. The birefringence of the resonator permits the simple extraction of an error signal by using one polarization state as a phase reference for another state. No modulation of the light or the resonator is required, reducing the complexity of the laser locking setup.