Seismic isolation enhancements for initial and advanced LIGO

A seismic isolation system for the proposed 'Advanced LIGO' detector upgrade is under development. It consists of a two-stage in-vacuum active isolation platform that is supported by an external hydraulic actuation stage. A full-scale preliminary-design technology demonstrator of the in-vacuum platform has been assembled and is being tested at Stanford's engineering test facility. Unanticipated excess ground motion from local human activity at LIGO Livingston has prompted accelerated development of the external stage for installation and use in the initial Livingston detector. As an interim measure, active external isolation in the laser beam direction is implemented using existing PZT external actuators.