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Technologies 2014, 2(3), 129-142; doi:10.3390/technologies2030129
Article

A 100-m Fabry–Pérot Cavity with Automatic Alignment Controls for Long-Term Observations of Earth’s Strain

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Received: 29 April 2014 / Revised: 27 June 2014 / Accepted: 15 July 2014 / Published: 6 August 2014
(This article belongs to the Special Issue Precision Measurements and Metrology Using Lasers)
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Abstract

We have developed and built a highly accurate laser strainmeter for geophysical observations. It features the precise length measurement of a 100-m optical cavity with reference to a stable quantum standard. Unlike conventional laser strainmeters based on simple Michelson interferometers that require uninterrupted fringe counting to track the evolution of ground deformations, this instrument is able to determine the absolute length of a cavity at any given time. The instrument offers advantage in covering a variety of geophysical events, ranging from instantaneous earthquakes to crustal deformations associated with tectonic strain changes that persist over time. An automatic alignment control and an autonomous relocking system have been developed to realize stable performance and maximize observation times. It was installed in a deep underground site at the Kamioka mine in Japan, and an effective resolution of 2 × (10−8 − 10−7) m was achieved. The regular tidal deformations and co-seismic strain changes were in good agreement with those from a theoretical model and a co-located conventional laser strainmeter. Only the new instrument was able to record large strain steps caused by a nearby large earthquake because of its capability of absolute length determination.
Keywords: absolute distance determination; earthquake monitoring; laser strainmeter; optical cavity alignment absolute distance determination; earthquake monitoring; laser strainmeter; optical cavity alignment
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Takamori, A.; Araya, A.; Morii, W.; Telada, S.; Uchiyama, T.; Ohashi, M. A 100-m Fabry–Pérot Cavity with Automatic Alignment Controls for Long-Term Observations of Earth’s Strain. Technologies 2014, 2, 129-142.

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