2019 Fiscal Year Research-status Report
Crystalline mirrors with minimal thermo-optic noise for space-time metrology
| Project/Area Number |
19K03897
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| Research Institution | National Astronomical Observatory of Japan |
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Principal Investigator |
フラミニオ ラファエレ 国立天文台, 重力波プロジェクト, 特任教授 (10723108)
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| Co-Investigator(Kenkyū-buntansha) |
LEONARDI MATTEO 国立天文台, 重力波プロジェクト, 助教 (90816448)
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| Project Period (FY) |
2019-04-01 – 2022-03-31
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| Keywords | gravitational wave / mirror / crystal / optical coating / thermal noise |
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| Outline of Annual Research Achievements |
Part of this year activity has consisted in making a careful evaluation of thermo-elastic and thermo-refractive noise in the case of small beams reflected on GaAs/AlAs coatings. A technical note on this is in preparation.
In collaboration with CMS we realized a 1 inch GaAs/AlAs mirror optimized to minimize coating thermal noise. Both the mirror roughness and mirror scattering were measured. The coating defects were also examined and counted. A mirror map showing all the defects was obtained. Overall, the quality of the coating is very good, comparable to the one already obtained in the case of quarter wavelength coatings.
The calibration procedure usually performed with the PCI systems relays on the comparison of the absorption signal between a reference sample with known absorption and the sample of which we want to know the absorption. This approach has some problem when used to calibrate crystalline coating absorption since the calibration sample has different properties with respect to the crystalline coating one. In order to circumvent this problem, a 633nm beam was set up to perform what is usually called auto-calibration.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
No special reasons, work progressing as well as possible given the constraints and the results.
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| Strategy for Future Research Activity |
The first task will be to issue the technical note describing thermo-optic noise in crystalline coatings illuminated with small beams like those used in table-top optical cavities.
Then we want to proceed with the further optical characterization of the 1 inch crystalline mirror that we already produced. This will be followed by the first measurement of its thermal noise using a high finesse cavity.
In parallel, we want to start the production of larger diameter crystalline coatings (10 cm diameter) on GaAs substrate. This will be used to study and possible optimize the transfer technique on silica wafers. Different type of multi-layer stacks will be realized to this purpose. The optical characterization of these coatings will be part of this fiscal year work.
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