Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Expansivity of fused quartz glass measured within 6 x 10^-10 /K

Published

Author(s)

Patrick Egan

Abstract

Thermal expansion sometimes dominates uncertainty in a precision measurement. A cell-based refractometer has been designed at NIST which targets 10^-6 relative uncertainty in the measurement of helium refractivity; in terms of absolute refractive index at ambient conditions, the accuracy goal is 3 × 10^-11. To achieve this level of accuracy, the length of a 0.5 m gas cell would need to be known within 100 nm. This is achievable when cell length is measured by coordinate-measuring machine at 20 degC. However, the refractometer will operate at the thermodynamically known fixed-points of water and gallium, near 0 degC and 30 degC, respectively. The cell is made from fused quartz glass, which has a nominal thermal expansion coefficient of 0.4 (µm/m)/K. Therefore, to scale the accuracy of the dimensional metrology across 20 degC to the triple-point of water requires that the thermal expansion coefficient of fused quartz glass is known within 10 (nm/m)/K, or 2.5 %. A method is described to measure the thermal expansion coefficient of fused quartz glass. The measurement principle is to monitor the change in resonance frequency of a Fabry–Perot cavity as its temperature changes; the Fabry–Perot cavity is made from fused quartz glass. The standard uncertainty in the measurement was less than 0.6 (nm/m)/K, or 0.15 %. The limit on performance is arguably uncertainty in the reflection phase-shift temperature dependence, because neither thermooptic nor thermal expansion coefficients of thinfilm coatings are reliably known. However, several other uncertainty contributors are at the same level of magnitude, and so any improvement in performance would entail significant effort. Furthermore, measurements of three different samples revealed that material inhomogeneity leads to differences in the effective thermal expansion coefficient of fused quartz; inhomogeneity in thermal expansion among samples is 24 times larger than the measurement uncertainty in a single sample.
Citation
NCSLI Measure
Volume
15
Issue
1

Keywords

thermal expansion, dimensional metrology, reference material

Citation

Egan, P. (2023), Expansivity of fused quartz glass measured within 6 x 10^-10 /K, NCSLI Measure, [online], https://doi.org/10.51843/measure.15.1.5, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=935332 (Accessed July 14, 2024)

Issues

If you have any questions about this publication or are having problems accessing it, please contact reflib@nist.gov.

Created December 20, 2023, Updated December 21, 2023