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Laser-interferometer application to broadband observations

Akito ARAYA (Earthquake Research Inst., Univ. of Tokyo, Japan). Broadband observation … requires low-frequency sensitivity. Advantages of Laser Interferometers: ・ high resolution owing to short wavelength of light

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Laser-interferometer application to broadband observations

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  1. Akito ARAYA (Earthquake Research Inst., Univ. of Tokyo, Japan) Broadband observation … requires low-frequency sensitivity Advantages of Laser Interferometers: ・high resolution owing to short wavelength of light ・low drift using frequency-stabilized laser ・wide range by counting fringes ・in-situ calibration with reference to wavelength of light ・free from EM noise or heating based on optical sensing ・operation at high-temperature (deep borehole) Laser-interferometer application to broadband observations

  2. Application I ・・・・・・ an inertia accelerometer Features of the laser-interferometric seismometer ・Laser-diode as a light source (l=850nm, 5mW) ・Long-period pendulum (f0=7s with a 10-cm mass) ・Self calibration (with reference to the laser wavelength) ・Wideband feedback (UGF=1kHz, phase delay < 0.2deg. below 100Hz) Prototype laser seismometer Block diagram

  3. ・Accuracy of the self calibration ----- ~1% as compared with an STS-2 seismometer ・Self-noise level ----- well below the Low Noise Model (50mHz ~ 100Hz) estimated from two identical laser seismometers Comparison with an STS-2 seismometer Self-noise estimation (measured at Black Forest Obs.)

  4. Optical-fiber-linked version of a laser seismometer (under development) Accelerometer and an air-tight case No electronic components are installed in the accelerometer Accelerometer (vertical)

  5. Application II ・・・・・・ a long-baseline strainmeter Laser strainmeter as a broadband seismometer ・Iodine-stabilized Nd:YAG laser (l =532nm, dn/n=2×10-13) ・100-m baseline, 1000-m underground (in Kamioka Mine)

  6. Comparison with CMG seismometers Tokachi (Hokkaido, Japan) earthquake (M=8.0) No saturation by fringe counting

  7. Summany Laser interferometer … promising method for ・opening up a new window (deep borehole, ocean floor, etc.) optical-fiber-linked borehole seismometer, tiltmeter, and strainmeter ・improving sensitivity long-baseline extensometer with a highly-stabilized laser The details are shown in POSTER.

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