Physics of interferometric gravitational wave detectors
The Caltech-MIT joint LIGO project is operating three long-baseline interferometers (one of 2 km and two of 4 km) in order to unambiguously measure the infinitesimal displacements of isolated test masses which convey the signature of gravitational waves from astrophysical sources. An interferometric gravitational wave detector like LIGO is a complex, non-linear, coupled, dynamic system. This article summarizes various interesting design characteristics of these detectors and techniques that were implemented in order to reach and maintain its operating condition. Specifically, the following topics are discussed: (i) length sensing and control, (ii) alignment sensing and control and (iii) thermal lensing which changes the performance and operating point of the interferometer as the input power to LIGO is increased.
© Indian Academy of Sciences 2004. Thanks to all LIGO Laboratory colleagues at Caltech, MIT and the Observatory sites at Hanford and Livingston for various studies and measurements which have been used to illustrate various issues in this article. Special thanks are due to M Evans, A Lazzarini, H Radkins, R Savage and Hiro Yamamoto for their help and comments. The LIGO Observatories were constructed by the California Institute of Technology and Massachusetts Institute of Technology with funding from the National Science Foundation under cooperative agreement PHY 9210038. The LIGO Laboratory operates under cooperative agreement PHY-0107417. This article is assigned LIGO document number LIGO-P040005-00-E.