Effects of mode degeneracy in the LIGO Livingston Observatory recycling cavity
Abstract
We analyze the electromagnetic fields in a Pound-Drever-Hall locked, marginally unstable, Fabry-Perot cavity as a function of small changes in the cavity length during resonance. More specifically, we compare the results of a detailed numerical model with the behavior of the recycling cavity of the Laser Interferometer Gravitational-wave Observatory (LIGO) detector located in Livingston, Louisiana. In the interferometer's normal mode of operation, the recycling cavity is stabilized by inducing a thermal lens in the cavity mirrors with an external CO2 laser. During our study, this thermal compensation system was not operating, causing the cavity to be marginally optically unstable and cavity modes to become degenerate. In contrast to stable optical cavities, the modal content of the resonating beam in the uncompensated recycling cavity is significantly altered by very small cavity length changes. This modifies the error signals used to control the cavity length in such a way that the zero crossing point is no longer the point of maximum power in the cavity, nor is it the point where the input-beam mode in the cavity is maximized.
Additional Information
© 2007 Optical Society of America. Received July 12, 2007; revised September 1, 2007; accepted September 7, 2007; posted September 18, 2007 (Doc. ID 85108); published October 17, 2007. The continuing and reliable operation of the LIGO interferometer at Livingston was made possible by the hard work of our many commissioning colleagues. Rana Adhikari taught one of the authors (AMG) how to understand the LIGO Livingston interferometer and also provided useful comments for the paper. David Ottaway read versions of the manuscript and shared insights based on his considerable knowledge of interferometer optics. He was also one of the first people to appreciate the importance of the non-Gaussian structure of the sidebands in the LLO recycling cavity, first seen during installation and commissioning of the LLO phase camera with one of the authors (AMG). Bill Kells and David Ottaway provided information about the LHO results, and Bill Kells pioneered the application of the Eikonal optical model. The authors thank Riccardo DeSalvo and David Reitze for encouraging the submission of the manuscript for publication. Finally, Keita Kawabe provided a careful internal (LSC) review of the manuscript and made observations leading to improvements. LIGO was constructed by the California Institute of Technology and Massachusetts Institute of Technology with funding from the National Science Foundation and operates under cooperative agreement PHY-0107417. This paper has LIGO Document Number LIGO-P070044-02-Z.Files
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Additional details
- Eprint ID
- 9463
- Resolver ID
- CaltechAUTHORS:GREjosab07
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2008-01-07Created from EPrint's datestamp field
- Updated
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2019-10-03Created from EPrint's last_modified field