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28 April 2008 Subnanometric Michelson interferometry for seismological applications
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A digital seismic measuring chain is an electromechanical system able to record the lowest natural ground motions observable on Earth but also to measure signals from largest earthquakes. Its cornerstones are an inertial seismometer and a digitizer. As equipments available on the market don't answer to all seismological applications CEA/DASE (Commissariat a l'Energie Atomique/Departement analyse, surveillance, environnement) is interested in, it has developed the adequate digital seismic measuring chains. Today, the technologies used have reached their maturity. New sensing techniques need to be developed. Optical sensors are now widely used in vibrometry and displacement measurements. Such devices generally use interferometry to achieve subnanometric resolution with a large dynamic range. We have developed a prototype digital motion transducer from a Michelson interferometer in order to evaluate the potential of this technology for seismological applications. Tests were carried out to validate the operation of this transducer and to estimate its main characteristics for seismological applications. We focused on transducer motion range and intrinsic noise. Results are promising. Prototype intrinsic noise reaches levels as small as 100 fm/√Hz around 8 Hz and is better than that of present transducers all over the bandwidth of interest, motion range also. Interesting seismological applications can be considered leading to more accurate seismic measuring chains, easier to manufacture, deploy and operate.
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D. Ponceau, P. Millier, and S. Olivier "Subnanometric Michelson interferometry for seismological applications", Proc. SPIE 7003, Optical Sensors 2008, 70030U (28 April 2008);

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