Advanced LIGO

TL;DR

Advanced LIGO is a significant upgrade over initial LIGO, featuring enhanced sensitivity and lower frequency detection capabilities, enabling more effective gravitational wave observations with improved technology and design.

Contribution

This paper details the design and technological improvements of Advanced LIGO, achieving tenfold sensitivity enhancement and lower frequency detection compared to initial LIGO.

Findings

Sensitivity improved by a factor of 10 around 100 Hz

Lower frequency detection down to 10 Hz

Implementation of signal recycling for better frequency response

Abstract

The Advanced LIGO gravitational wave detectors are second generation instruments designed and built for the two LIGO observatories in Hanford, WA and Livingston, LA. The two instruments are identical in design, and are specialized versions of a Michelson interferometer with 4 km long arms. As in initial LIGO, Fabry-Perot cavities are used in the arms to increase the interaction time with a gravitational wave, and power recycling is used to increase the effective laser power. Signal recycling has been added in Advanced LIGO to improve the frequency response. In the most sensitive frequency region around 100 Hz, the design strain sensitivity is a factor of 10 better than initial LIGO. In addition, the low frequency end of the sensitivity band is moved from 40 Hz down to 10 Hz. All interferometer components have been replaced with improved technologies to achieve this sensitivity gain. Much better seismic isolation and test mass suspensions are responsible for the gains at lower frequencies. Higher laser power, larger test masses and improved mirror coatings lead to the improved sensitivity at mid- and high- frequencies. Data collecting runs with these new instruments are planned to begin in mid-2015.