Direct measurement of coating thermal noise at low temperatures with a folded optical cavity

• Project/Area Number: 18K03681
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 15020:Experimental studies related to particle-, nuclear-, cosmic ray and astro-physics
• Research Institution: National Astronomical Observatory of Japan
• Principal Investigator: Aso Yoichi 国立天文台, 重力波プロジェクト, 准教授 (10568174)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Project Status: Completed (Fiscal Year 2020)
• Budget Amount: ¥4,420,000 (Direct Cost: ¥3,400,000、Indirect Cost: ¥1,020,000); Fiscal Year 2020: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000); Fiscal Year 2019: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000); Fiscal Year 2018: ¥1,950,000 (Direct Cost: ¥1,500,000、Indirect Cost: ¥450,000)
• Keywords: 重力波 / 低温 / 薄膜 / 熱雑音 / コーティング

Outline of Final Research Achievements

In order to reduce the thermal noise, which is one of the main noises of gravitational wave detectors, mirrors are cooled down to a cryogenic temperature in the next generation detectors. However, an adsorbed molecular layer is formed on the surface of such a mirror with time, which increases the optical loss. We have developed a method to simultaneously measure the optical loss and thickness of the cryogenic molecular layer (CML) using a folded optical cavity. The absorption coefficient of the CML was determined by this method, and it was found to be almost the same as the literature value for amorphous ice.
The results of this study indicate that the next generation gravitational wave detectors using silicon mirrors require measures such as the suppression of CML formation by adding low-temperature baffles and/or the heating and desorption of CMLs using a CO2 laser.

Academic Significance and Societal Importance of the Research Achievements

本研究では、真空中で鏡表面に形成される薄膜の光学損失と、膜厚を同時に測定する手法を開発することに成功した。またこれを用いて低温鏡の表面に形成される吸着分子層の吸収係数を求めることにも成功した。これは次世代低温重力波検出器の設計に重要な示唆を与える結果である。本研究の成果を活用することで、低温バッフルや、分子層除去システムの設計を最適化することができる。

Research Products

• [Journal Article] Optical loss study of the cryogenic molecular layer using a folded cavity for future gravitational-wave detectors (2021)
  • Author(s): Tanioka Satoshi、Aso Yoichi
  • Journal Title: Optics Express Volume: 29 Issue: 5 Pages: 6780-6793
  • DOI: 10.1364/oe.415921
  • Peer Reviewed / Open Access
• [Journal Article] Optical loss study of molecular layer for a cryogenic interferometric gravitational-wave detector (2020)
  • Author(s): Tanioka Satoshi、Hasegawa Kunihiko、Aso Yoichi
  • Journal Title: Physical Review D Volume: 102 Issue: 2 Pages: 022009-022009
  • DOI: 10.1103/physrevd.102.022009
  • Peer Reviewed
• [Journal Article] First cryogenic test operation of underground km-scale gravitational-wave observatory KAGRA (2019)
  • Author(s): Akutsu T, et al. (KAGRA Collaboration)
  • Journal Title: Classical and Quantum Gravity Volume: 36 Issue: 16 Pages: 165008-165008
  • DOI: 10.1088/1361-6382/ab28a9
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Measuring scattering light distributions on high-absorptive surfaces for stray-light reduction in gravitational-wave detectors (2019)
  • Author(s): Zeidler Simon、Akutsu Tomotada、Torii Yasuo、Aso Yoichi
  • Journal Title: Optics Express Volume: 27 Issue: 12 Pages: 16890-16890
  • DOI: 10.1364/oe.27.016890
  • Peer Reviewed / Open Access
• [Journal Article] Demonstration of Displacement Sensing of a mg-Scale Pendulum for mm- and mg-Scale Gravity Measurements (2019)
  • Author(s): N. Matsumoto, S. B. Catano-Lopez, M. Sugawara, S. Suzuki, N. Abe, K. Komori, Y. Michimura, Y. Aso, and K. Edamatsu
  • Journal Title: Phys. Rev. Lett. Volume: 122 Issue: 7 Pages: 071101-071101
  • DOI: 10.1103/physrevlett.122.071101
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Measurement of optical losses in a high-finesse 300 m filter cavity for broadband quantum noise reduction in gravitational-wave detectors (2018)
  • Author(s): E. Capocasa, Y. Guo, M. Eisenmann, Y. Zhao, A. Tomura, K. Arai, Y. Aso, M. Marchio, L. Pinard, P. Prat, K. Somiya, R. Schnabel, M. Tacca, R. Takahashi, D. Tatsumi, M. Leonardi, M. Barsuglia, and R. Flaminio
  • Journal Title: Phys. Rev. D Volume: 98 Issue: 2 Pages: 022010-022010
  • DOI: 10.1103/physrevd.98.022010
  • Peer Reviewed / Int'l Joint Research