High Power and Optomechanics in Advanced LIGO Detectors

In September 2015, a new era of astronomy began with the first direct detection of grav- itational waves from a binary black hole coalescence. The event was captured by the Laser Interferometer Gravitational-wave Observatory, comprised of two long-baseline interferometers, one in Livingston, LA and one in Hanford, WA. At the time of the first detection, the interferometers were part way through an upgrade to an advanced configuration and were operating with a strain sensitivity of just better than 10−23/Hz1/2 around 100Hz. The full Advanced LIGO design calls for sensitivity of a few parts in 10−24/Hz1/2. This thesis covers the detector upgrade to double the input power, thereby reducing quantum shot noise, which currently limits LIGO strain sensitivity above 100Hz. First, it presents the design of the interferometer and the noises – fundamental, technical, and environmental – which contribute to the full sensitivity curve, motivating the need for high power. The details of the high power laser upgrade are discussed. Second, it presents select side effects of high power, which can result in overall losses and heighten specific classical noise couplings. The work particularly focuses on a three-mode opto-mechanical interaction that can become unstable at high power, threatening the operational ability of the detector; multiple successful mitigation technique are presented and compared. The results of this work, combined with the collaborative work of many others, allow the Advanced LIGO detectors to achieve a strain sensitivity better than 5 × 10−24/Hz1/2 during the third observation run

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. One proposed technique to stabilize parametric instability is active damping of acoustic modes. We report here the first demonstration of damping a parametrically unstable mode using active feedback forces on the cavity mirror. A 15 538 Hz mode that grew exponentially with a time constant of 182 sec was damped using electrostatic actuation, with a resulting decay time constant of 23 sec. An average control force of 0.03 nN was required to maintain the acoustic mode at its minimum amplitude

Effects of d-α-tocopherol supplements on lipid metabolism in a high-fat diet-fed animal model

High-fat diet up-regulates either insulin resistance or triglycerides, which is assumed to be related to the expression of peroxisome proliferator-activated receptor (PPAR)-α and PPAR-γ. The beneficial effects of vitamin E on insulin resistance are well known; however, it is not clear if vitamin E with a high-fat diet alters the expression of PPAR-α and PPAR-γ. We investigated the effects of d-α-tocopherol supplementation on insulin sensitivity, blood lipid profiles, lipid peroxidation, and the expression of PPAR-α and PPAR-γ in a high-fat (HF) diet-fed male C57BL/6J model of insulin resistance. The animals were given a regular diet (CON; 10% fat), a HF diet containing 45% fat, or a HF diet plus d-α-tocopherol (HF-E) for a period of 20 weeks. The results showed that the HF diet induced insulin resistance and altered the lipid profile, specifically the triglyceride (TG) and total cholesterol (TC) levels (P < 0.05). In this animal model, supplementation with d-α-tocopherol improved insulin resistance as well as the serum levels of TG and very-low-density lipoprotein-cholesterol (VLDL-C) (P < 0.05). Moreover, the treatment decreased the levels of malondialdehyde (MDA) in the serum and liver while increasing hepatic PPAR-α expression and decreasing PPAR-γ expression. In conclusion, the oral administration of d-α-tocopherol with a high-fat diet had positive effects on insulin resistance, lipid profiles, and oxidative stress through the expression of PPAR-α and PPAR-γ in a high-fat diet-fed male mice

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 nano-meter scale thermo-elastic deformations and substrate lenses from these micron-scale absorbers significantly reduces 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 build-up in second generation gravitational wave detectors (dual-recycled Fabry-Perot Michelson interferometers). This analysis predicts that the power-dependent reduction in interferometer performance will significantly degrade maximum stored power by up to 50% and hence, limit GW sensitivity, but suggests system wide corrections that can be implemented in current and future GW detectors. This is particularly pressing given that future GW detectors call for an order of magnitude more stored power than currently used in Advanced LIGO in Observing Run 3. We briefly review strategies to mitigate the effects of point absorbers in current and future GW wave detectors to maximize the success of these enterprises.Comment: 49 pages, 16 figures. -V2: typographical errors in equations B9 and B10 were corrected (stray exponent of "h" was removed). Caption of Figure 9 was corrected to indicate that 40mW was used for absorption in the model, not 10mW as incorrectly indicated in V