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Matters of Gravity
LIGO Update for Spring 1996

by Stan Whitcomb

     Construction continues to move forward rapidly at both LIGO sites (Hanford Washington and Livingson, Louisiana). The rough grading activities at the Louisiana site are underway, and in Washington a contract to begin the construction of the 8 kilometers of foundations which will support the beam tube has been awarded. Our Architect/Engineering contractor (Ralph M. Parsons Co.) has completed the preliminary design for the buildings and associated site development. Parsons is now coninuing with the final design effort, and the preparation of the bid packages for the construction contracts.

     Significant milestones were also achieved on the other major elements of the LIGO facilities. A contract for the construction of the LIGO beam tubes (which connect the vertex and ends of the two arms) was signed with Chicago Bridge and Iron, the company that performed the successful demonstration test last year. They are preparing for full production of the LIGO beam tubes and plan to begin installation by fall of this year. The contact for the final design, fabrication and installation of the remainder of the vacuum system was signed with Process Systems International, and they have begun intensive design work. This design work is scheduled to be complete by summer and will be followed by fabrication of the hardware to be delivered to the sites.

     LIGO helped to organize a second Aspen Winter Physics Conference on Gravitational Waves from January 15-21, 1996. In addition to the usual technical interchanges among the experimenters present from the various groups around the world, there was a special emphasis on data analysis and the intereraction between experiment and theory in the analysis of LIGO data. The conference was also the first meeting of the LIGO Research Community, an organization of people interested in LIGO science. Another meeting of the LIGO Research Community will take place at the May APS meeting in Indianapolis.

     A major effort in LIGO has been to push forward the design of the LIGO detectors. After careful consideration, the LIGO Project has made a working decision to switch its baseline interferometer design to solid-state lasers operating in the near-infrared in place of Argon ion lasers operating in the green. The new lasers are expected to result in comparable sensitivity and higher reliability in the initial interferometers. This decision also defines a clear path for later improvements to the initial interferometers taking advantage of rapidly progressing solid-state laser technology, and will permit closer cooperation with other gravitational wave groups who have generally adopted solid state near-infrared lasers for their detectors.

     In the R&D program, investigations of noise on the 40m interferometerat Caltech continued. The 40 m interferometer has been converted to an optically recombined system, and will be converted to a recycled configuration later this year. At MIT, the initial phase of research with a suspended interferometer to investigate optical sources of noise has been completed. This interferometer, initially configured as a simple Michelson to emphasize the study of optical sources of noise and to minimize the amount of time needed to debug other noise sources, has been fully characterized. The next step, that of adding a recycling mirror to increase the optical power incident on the beamsplitter, is underway.

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Last modified February 13, 1996