2002 Fiscal Year Final Research Report Summary
Study of low-loss materials for mirrors used in the next-generation gravitational wave detectors
| Project/Area Number |
13440070
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
素粒子・核・宇宙線
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| Research Institution | The University of Tokyo |
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Principal Investigator |
TSUBONO Kimio The University of Tokyo, Graduate School of Science, Professor, 大学院・理学系研究科, 教授 (10125271)
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| Co-Investigator(Kenkyū-buntansha) |
ANDO masaki The University of Tokyo, Graduate School of Science, Research Associate, 大学院・理学系研究科, 助手 (90313197)
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| Project Period (FY) |
2001 – 2002
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| Keywords | gravitational wave / laser interferometer / mirror / fused silica / low-loss / mono-crystalline / thermal noise / precise measurement |
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| Research Abstract |
Investigating the mechanical loss of low-loss samples has been an important, but difficult, subject in the field of detecting gravitational-waves. The thermal motion of the internal mode of the mirrors is considered to be one of the fundamental noise sources which limits the sensitivities of gravitational-wave detectors. The amplitude of the thermal motion is proportional to the square root of the mechanical loss of the mirror. Therefore, it is significant to investigate the intrinsic loss of the materials for the mirror to estimate the sensitivity limit of gravitational-wave detectors, and to improve it by finding lower loss materials. However, the loss of low-loss samples is difficult to measure because of the loss due to the support for the measurement.
We have developed a method to measure the mechanical loss of cylindrical samples. By using our nodal support technique, the loss due to the support can be excluded. We evaluated separately the intrinsic loss of the material and the loss due to the surface roughness by systematically analyzing the measured losses.
Then, we measured the mechanical loss of crystalline anisotropic samples, silicon and sapphire, using a nodal support. Measured quality factor of the silicon sample reached 1.0 x 10^8 at room temperature. The sapphire sample showed lower quality factors, 6.4 x 10^7 at most, which were analytically confirmed to be dominated by surface loss.
Also, we systematically measured and compared the mechanical-losses of various kinds of bulk fused silica. Their quality factors widely ranged from 7 x 10^5 to 4 x 10^7, the latter being the highest reported among fused silica mirror substrates. We observed the frequency dependence of Qs. We also found increase in Qs by an annealing.
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