研究目的
Investigating multilayer high reflectors with new coating materials (silicon nitride and silica) for next-generation laser interferometer gravitational wave detectors operated at cryogenic temperatures to reduce coating thermal noise and optical absorption.
研究成果
The silicon nitride and silica quarter-wave stacks show coating thermal noise within twice the lower limit for ET-LF and LIGO Voyager specifications and comparable to KAGRA, with lower noise than Advanced LIGO. Loss angles exhibit weak positive frequency dependence. Optical absorption is high at 45.9 ppm but can be reduced to 2 ppm using a multimaterial system. Future work should focus on thermal annealing and optimized layer designs to further reduce noise and absorption.
研究不足
The study assumes temperature-independent elastic constants for films due to lack of cryogenic measurements. Room-temperature loss angle analysis has uncertainties, leading to assumptions of equal bulk and shear losses. Optical absorption measurements are at room temperature, and cryogenic reductions are estimated but not directly measured. Post-deposition heat treatment effects are not fully explored, and the multimaterial system requires further experimental validation.
1：Experimental Design and Method Selection:
The study uses plasma-enhanced chemical vapor deposition (PECVD) to deposit amorphous silicon nitride and silica quarter-wave high-reflector stacks. Mechanical loss angles are measured using the cantilever ring-down method at room and cryogenic temperatures. Finite element method (FEM) simulations are employed to calculate bulk and shear energies and coating thermal noise.
2：Sample Selection and Data Sources:
Samples include cantilevers coated with 1 to 8 pairs of silicon nitride and silica bilayers deposited on silicon substrates. Data on material properties (e.g., refractive index, Young's modulus) are sourced from previous reports and measurements.
3：List of Experimental Equipment and Materials:
Equipment includes PECVD systems, cryogenic systems for ring-down measurements, transmission electron microscope for thickness measurement, and FEM software (COMSOL 4.4). Materials include silicon nitride (SiN0.40H0.79), silica (SiO2), silicon cantilevers, and precursors like SiH4, NH3, N2O.
4：4). Materials include silicon nitride (SiN40H79), silica (SiO2), silicon cantilevers, and precursors like SiH4, NH3, N2O.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: Coatings are deposited via PECVD with controlled parameters. Mechanical loss is measured by exciting cantilevers at resonant frequencies and measuring decay times. Cryogenic measurements are conducted from 10 K to 130 K. Optical properties are analyzed using simulation software.
5：Data Analysis Methods:
Data are analyzed using linear fits for loss angle frequency dependence, FEM for energy calculations, and theoretical models (e.g., Hong's model) for thermal noise evaluation. Statistical methods include error estimation from repeated measurements.
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