LIGO Document P2000016-v1
- 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.
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