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Matters of Gravity
LIGO Update for Fall 1995

by Sydney Meshkov and Stan Whitcomb

     Since the last Matters of Gravity report on LIGO in March, a number of significant events have occurred. Dedication ceremonies for the Louisiana LIGO site took place on July 6, 1995 at Livingson, Louisiana, exactly one year after a similar ceremony at the Hanford, Washington site. By now the clearing and grubbing activities at the Louisiana site have been completed and rough grading will begin shortly.

     Working with our Architect/Engineering contractor (Ralph M. Parsons Co.), LIGO has finalized the conceptual design for the buildings and associated site development. Parsons has now started the full design effort. The large scale demonstration test for the construction of the LIGO beam tubes (which connect the vertex and ends of the two arms) was successfully completed this spring, confirming that the design meets our vacuum and cleanliness requirements. A preliminary design competition for the remainder of the vacuum system was carried out and a contractor selected for the final design and fabrication effort.

     Organizationally, a LIGO pre-Program Advisory Committee has been formed, with Peter Saulson (Syracuse) as its chair. The other members are: S. Finn (Northwestern), A. Giazotto (Pisa), J. Hall (JILA), W. Hamilton (LSU), C. Prescott (SLAC), A. Ruediger (MPI-Garching). This committee will exist only for a year or two. During its brief life it will act as both a LIGO Program Advisory Committee (PAC) and as an External Advisory Committee (EAC). Before it goes out of existence it will help design a final PAC and EAC. The first meeting is scheduled for September 8-9, 1995 at Caltech.

     Following the very succesful Aspen Winter Physics Conference on Gravitational Waves and Their Detection (see Matters of Gravity, Number 5, Spring 1995), a second Aspen Winter Physics Conference has been scheduled for January 15-21, 1996. A major theme of the Conference will be the study of advanced interferometers and long range planning. The program will include extensive meetings of the LIGO Research Community, and several sessions on LISA.

     In the R&D program, the 40m interferometer at Caltech has been converted to an optically recombined system, as a first step toward operating it as a recycled interferometer. The optical configuration chosen for the optical recombination is modeled after that planned for the full-scale LIGO interferometers and uses a small asymmetry in the arms to produce the required modulation at the point where the difference in arm lengths is sensed. New servosystems required to hold the interferometer at its correct operating points are being testing on the 40 m system, and noise studies to understand the performance in the new configuration are underway.

     At MIT, a suspended interferometer to investigate optical sources of noise at high phase sensitivity is under development. This interferometer has a simple optical configuration, to emphasize the study of optical sources of noise and to minimize the amount of time needed to debug other noise sources. The initial phase of its fabrication has been completed and it is producing its first data, although still at relatively low power (about 50 mW). Over the next year, the power will be gradually increased, with a goal of achieving shot noise limited sensitivity with 70 W incident on the beamsplitter.

     The effort on the LIGO detectors is growing rapidly as projects move from the R&D to the actual detector detailed modeling and hardware design. A recent highlight in this effort was the integration of a stabilized argon ion laser under the control of EPICS. EPICS is the control system planned for the LIGO detectors, and this laser is the first detector subsystem to be fully interfaced to it to provide data logging and operator interfaces appropriate for a facility the scale of LIGO.

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Last modified October 19, 1995