LIGO project update

David Shoemaker, MIT

LIGO Installation is once again the focus of our efforts in the LIGO Lab. Because the activities are so hands-on, this Update is mostly in graphical form with the text serving as captions for the photographs which can be found at

We start (Fig. 1) with a view from space of the Livingston Observatory. The 4km arms are visible (as the clearing of the forest), and in the detailed view the 'X' shaped main building can be made out. Descending from angel to airplane height, we now see clearly the high-bay space containing the interferometer components on the right, the covered beam tubes in the background and to the right, and the entrance and offices in the right foreground. (The 'overpass' and the black water tank are fire precautions.)

A view inside the high bay (Fig 3), this time from Hanford, shows a number of the test-mass vacuum equipment chambers (the taller vertical cylinders), some 'HAM' multipurpose chambers (the two to the right), the main beam tubes (the large horizontal tubes to the far left and the right background), and a few of the many electronics racks. Navigating around the equipment involves lots of walking and climbing of stairs!

Several 2km sections of the beam tube (Fig 4) have been successfully 'baked out'--heated to drive off excess water and other contaminants. We see here a section of beam tube, wrapped in insulation, a heavy cable snaking across the floor to deliver current for heating. The concrete cover is arch-shaped.

A very significant effort is now underway in both Hanford and Livingston to install the seismic isolation system. Vacuum cleanliness requires 'bunny suits' (Fig 5); all of the equipment placed in the vacuum must be cleaned and baked as well, to guard against contamination of the mirrors. Fig 6 is a view after installation, with the bottom table, cylindrical masses and somewhat hidden springs between them, the top 'optics' table, and counterweights (emulating the final load) all visible.

The test masses, fused silica 25cm in diameter, are carefully characterized in a metrology interferometer (Fig 7), and mounted in a cage with a simple wire loop.

A detail of the point of departure of the wire is seen at the bottom left. The optical losses are determined by the polish and coating (and its cleanliness), and the mechanical losses are the point of connection with thermal noise, and so excruciating attention must be given to every detail.

The optics are installed (Fig 8) in the vacuum system and given an initial alignment sufficiently precise that the reflected beam will be correctly aligned to within one beam tube radius (0.5 m) over the length of the beam tube (4 km). Fancy surveying!

Our last image (Fig 9) shows a part of the optical table carrying the Pre-Stabilized Laser and some of the Input Optics (the University of Florida's contribution). The cylindrical vacuum system contains the frequency reference cavity for the laser, and the rectangular block of fused silica (developed at Stanford) is an optical cavity used in transmission to 'clean' the optical beam.

Our schedule calls for first tests of an interferometer using just the optics in the main building for this summer, with the full 4km paths included in the fall of '99. Please visit one of the sites if you are in the vicinity; contact and other information can be found at

Jorge Pullin