LIGO project status

Stan Whitcomb, Caltech

Construction continues to move forward rapidly at both LIGO sites (Hanford Washington and Livingston, Louisiana). At the Hanford site, construction of 8 kilometers of concrete foundations which will support the beam tubes has been completed. The final survey of the foundation along the two arms indicates that they are straight and level with an accuracy of 1.5 cm. Our Architect/Engineering contractor (Ralph M. Parsons Co.) completed the final design for the buildings. A contract with Levernier Construction Inc of Spokane Washington for the building construction was signed, and work is now underway. At the Louisiana site, the main activity is the rough grading (earthwork to level the site and to build up a berm on which the LIGO facility will be built). This work has gone more slowly than expected due to heavy rains, but is now nearing completion.

The vacuum system is also moving forward. Chicago Bridge and Iron, the company building the LIGO beam tubes (which connect the vertex and ends of the two arms), is installing its fabrication equipment in a facility near the Hanford site. They are preparing for full production of the LIGO beam tubes and plan to begin installation by fall of this year. The final design of the vacuum chambers and associated equipment which will be in the located in the buildings has been completed. Our contractor for this effort, Process Systems International, is now building the first large chambers.

The design of the LIGO detectors is accelerating, with most detector subsystems well into the preliminary design phase. Orders have already been placed for the fused silica that will be used for the test masses and other large optics. LIGO's decision to switch its baseline interferometer design to Nd:YAG lasers operating 1.06 microns has led to a development contract with Lightwave Electronics Corporation to develop a 10 W single frequency laser; first results from this development are expected near the end of the year.

In the R&D program, the 40 m interferometer has been converted to an optically recombined system as the first step toward recycling. The signal extraction and control topology in the recombined configuration is similar to that planned for the full-scale interferometers; a prime objective of this effort was to compare these signals with the results of modeling and in particular to study the problem of lock acquisition. At MIT, optical phase noise at the level of rad Hz are being investigated with a 5 m long suspended interferometer. This interferometer, initially configured as a simple Michelson, has now been converted to a recycled configuration. The increase in effective power due to recycling is approximately a factor of 500, leading to nearly 100 W incident on the beamsplitter. A detailed characterization of the noise is presently underway.

As an additional means of communicating up-to-the-minute information about LIGO, we have initiated a monthly newsletter. It can be accessed through our WWW home page at

Jorge Pullin
Sun Sep 1 16:45:26 EDT 1996