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Updated: Jun 14, 2026

Fabrication and Testing of Photonic Thermometers
Published on: October 24, 2018
Direct measurement of thermal fluctuation of high-Q pendulum
Kazuhiro Agatsuma1, Takashi Uchiyama, Kazuhiro Yamamoto
1Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan. agatsuma@icrr.u-tokyo.ac.jp
Abstract:
We have achieved a direct measurement of the thermal fluctuation of a pendulum in an off-resonant and wide frequency region using a laser interferometric gravitational-wave detector. These measurements have been well identified for over one decade by an agreement with a theoretical prediction, which is derived by a fluctuation-dissipation theorem. Thermal fluctuation was dominated by the contribution of resistances in coil-magnet actuator circuits. When we tuned these resistances, the noise spectrum also changed according to a theoretical prediction. The measured thermal noise level corresponds to a high quality factor on the order of 10(5) of the pendulum.
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