LIGO consist of two detector facilities, one is located at Hanford Reservation, Washington and the other at Livingston Parish, Louisiana. Each installation is configured in L-shaped with 4 km (2.5 mile) long arms, enclosing along its entire length an ultra high vacuum stainless steel beam tube, approximately 1.2 m in diameter, and interconnecting chambers. The beam tube will provide a path for the propagation of laser beams between the chambers.
The LIGO installation at the Washington site will consist of five stations connected by beam tube modules (each 2 km in length). The corner station, two end stations, and two mid stations will house and provide access to the vacuum system and interferometer components, vacuum equipment, and instruments. Full-length interferometers will be made up of components installed in the corner stations and end stations; half-length interferometer components will be installed at corner station and mid stations.
The installation at Livingston, Louisiana is similar to that shown in Fig.1 for Hanford, WA , except that it will have no half-length interferometers, thus no mid stations, and the corner station will be smaller.