研究目的
To propose a design for a laser refractometer that reduces uncertainty due to changes in window pathlength, aiming for a fractional error of less than 3 × 10?6 in the measurement of helium refractivity.
研究成果
The proposed quadruple-cell design with fused-silica windows is expected to reduce uncertainty due to changes in window pathlength by a factor of 3 compared to previous designs, enabling realizations of either the pascal or kelvin to within 3 × 10?6 relative standard uncertainty through helium refractivity measurements.
研究不足
The study identifies that an alternative design with sapphire windows and a low thermal expansion spacer, while reducing pressure-induced changes in pathlength, introduces concerns due to mismatch in thermal expansion and resulting temperature-induced changes in pathlength.
1：Experimental Design and Method Selection:
The study involves the design of a quadruple-cell laser refractometer to minimize pathlength uncertainty caused by window deformation and stress. Finite-element and photoelastic calculations are used to analyze the design.
2：Sample Selection and Data Sources:
The study focuses on the measurement of helium refractivity using the proposed refractometer design.
3：List of Experimental Equipment and Materials:
The design considers fused-silica and sapphire windows, with a spacer of low thermal expansion glass-ceramic for the sapphire windows.
4：Experimental Procedures and Operational Workflow:
The proposed design aims to reduce the area upon which the pressure acts and increase the elastic modulus of the window material to minimize pathlength changes.
5：Data Analysis Methods:
The analysis involves calculating the change in optical pathlength through windows and the sensitivity of the window pathlength to changes in beam location.
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