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).

First Demonstration of Electrostatic Damping of Parametric Instability at Advanced LIGO.

Interferometric gravitational wave detectors operate with high optical power in their arms in order to achieve high shot-noise limited strain sensitivity. A significant limitation to increasing the optical power is the phenomenon of three-mode parametric instabilities, in which the laser field in the arm cavities is scattered into higher-order optical modes by acoustic modes of the cavity mirrors. The optical modes can further drive the acoustic modes via radiation pressure, potentially producing an exponential buildup.

The advanced LIGO input optics.

The advanced LIGO gravitational wave detectors are nearing their design sensitivity and should begin taking meaningful astrophysical data in the fall of 2015. These resonant optical interferometers will have unprecedented sensitivity to the strains caused by passing gravitational waves. The input optics play a significant part in allowing these devices to reach such sensitivities.

Observation of Parametric Instability in Advanced LIGO.

Parametric instabilities have long been studied as a potentially limiting effect in high-power interferometric gravitational wave detectors. Until now, however, these instabilities have never been observed in a kilometer-scale interferometer. In this Letter, we describe the first observation of parametric instability in a gravitational wave detector, and the means by which it has been removed as a barrier to progress.

Control and tuning of a suspended Fabry-Perot cavity using digitally enhanced heterodyne interferometry.

We present the first demonstration of real-time closed-loop control and deterministic tuning of an independently suspended Fabry-Perot optical cavity using digitally enhanced heterodyne interferometry, realizing a peak sensitivity of ~10 pm/√Hz over the 10-1000 Hz frequency band. The methods presented are readily extensible to multiple coupled cavities. As such, we anticipate that refinements of this technique may find application in future interferometric gravitational-wave detectors.

Arm-length stabilisation for interferometric gravitational-wave detectors using frequency-doubled auxiliary lasers.

Residual motion of the arm cavity mirrors is expected to prove one of the principal impediments to systematic lock acquisition in advanced gravitational-wave interferometers. We present a technique which overcomes this problem by employing auxiliary lasers at twice the fundamental measurement frequency to pre-stabilise the arm cavities' lengths. Applying this approach, we reduce the apparent length noise of a 1.

Tip-tilt mirror suspension: beam steering for advanced laser interferometer gravitational wave observatory sensing and control signals.

We describe the design of a small optic suspension system, referred to as the tip-tilt mirror suspension, used to isolate selected small optics for the interferometer sensing and control beams in the advanced LIGO gravitational wave detectors. The suspended optics are isolated in all 6 degrees of freedom, with eigenmode frequencies between 1.3 Hz and 10 Hz.

Stable transfer of an optical frequency standard via a 4.6 km optical fiber.

We present a technique for the stable transfer of an optical frequency reference over a kilometer-scale optical fiber link. This technique implements phase measurements and laser feedback to cancel out the phase fluctuations that are introduced to an optical frequency standard as it passes through the fiber. We also present results for a bench top experiment, developed for the Advanced LIGO lock acquisition system, where this technique is implemented to phase-lock two Nd:YAG lasers, through a 4.