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Technische Universitaet Muenchen, Forschungseinrichtung Satellitengeodaesie Fundamentalstation Wettzell, 93444 Bad Kötzting, Germany schreiber{at}fs.wettzell.de
Department of Earth and Environmental Sciences, Ludwig-Maximilians-University Munich, Theresienstrasse 41, D-80333 Munich, Germany
Technische Universitaet Muenchen, Forschungseinrichtung Satellitengeodaesie Fundamentalstation Wettzell, 93444 Bad Kötzting, Germany
Department of Earth and Environmental Sciences, Ludwig-Maximilians-University Munich, Theresienstrasse 41, D-80333 Munich, Germany
Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0225
Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch 8020, New Zealand
Since the discovery of the wave nature of light, optical interferometry has assumed an important place in high precision metrology. This is mostly due to the inherent high sensor resolution for operational wavelengths in the vicinity of several hundred nanometers. In this context, interferometers in the Michelson configuration are most prominently used in gravitational wave antennas, such as the large projects VIRGO, LIGO, TAMA, and GEO600. In the Sagnac configuration they are used for high resolution rotation monitoring such as the precise observation of Earth rotation. Modern large-scale ring lasers reach a sensitivity for the measurement of rotation of 1 prad/sec (with approximately 1 hr of averaging). Because of the comparatively short wavelengths employed, optical interferometers are extremely sensitive to small mechanical perturbations of the entire apparatus. These can be caused by deformations, thermal or mechanical stress, and instabilities in the alignment of the optical components at the level of about 
/100. Ring lasers suitable for geophysical applications require a sensor resolution in the range of 10-8 rad/sec and below. This demands a scale factor of the instrument that is only achievable with mechanical dimensions of the interferometer on the order of about 1 m2 or larger. At the same time the necessary mechanical rigidity of the entire instrument has to be on the order of 5 nm. Currently, this has only been achieved with monolithic ring lasers made from blocks of Zerodur and installed in a temperature stabilized underground environment. However if long-term sensor stability is not required, compromises can be made and, in particular for studies of regional seismic events, it becomes feasible to build a heterolithic rotation sensor in a simpler and much cheaper way. Here, we report the design and first results from the GEOsensor, which has been specifically constructed for studies in rotational seismology. The sensor is operated at the Piñon Flat Seismological Observatory in Southern California.
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  W. H. K. Lee, H. Igel, and M. D. Trifunac Recent Advances in Rotational Seismology Seismological Research Letters, May 1, 2009; 80(3): 479 - 490. [Full Text] [PDF]
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 W. H. K Lee, M. Celebi, M. I. Todorovska, and H. Igel Introduction to the Special Issue on Rotational Seismology and Engineering Applications Bulletin of the Seismological Society of America, May 1, 2009; 99(2B): 945 - 957. [Abstract] [Full Text] [PDF]
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N. D. Pham, H. Igel, J. Wassermann, A. Cochard, and U. Schreiber The Effects of Tilt on Interferometric Rotation Sensors Bulletin of the Seismological Society of America, May 1, 2009; 99(2B): 1352 - 1365. [Abstract] [Full Text] [PDF]
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R. W. Dunn, H. H. Mahdi, and H. J. Al-Shukri Design of a Relatively Inexpensive Ring Laser Seismic Detector Bulletin of the Seismological Society of America, May 1, 2009; 99(2B): 1437 - 1442. [Abstract] [Full Text] [PDF]
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