Optical $$n(p,\ T_{90})$$ Measurement Suite 1: He, Ar, and N$$_2$$

A suite of measurements of refractive index $$n(p,\ T_{90})$$ n ( p , T 90 ) is reported for gas phase ordinary water H$$_2$$ 2 O and heavy water D$$_2$$ 2 O. The methodology is optical refractive index gas metrology, operating at laser wavelength $$633\ \text {nm}$$ 633 nm and covering the range $$(293< T_{90} < 433)\ \text {K}$$ ( 293 < T 90 < 433 ) K and $$p < 2\ \text {kPa}$$ p < 2 kPa . A key output of the work is the determination of molar polarizabilities $$A_{\text {R}} = 3.7466(18) \cdot [1 + 1.5(6) \times 10^{-6} (T/\text {K} - 303) ]\ \text{cm}^3 \cdot \text{mol}^{-1}$$ A R = 3.7466 ( 18 ) · [ 1 + 1.5 ( 6 ) × 10 - 6 ( T / K - 303 ) ] cm 3 · mol - 1 for ordinary water, and $$A_{\text {R}} = 3.7135(18) \cdot [1 + 4.4(10) \times 10^{-6} (T/\text {K} - 303) ]\ \text{cm}^3 \cdot \text{mol}^{-1}$$ A R = 3.7135 ( 18 ) · [ 1 + 4.4 ( 10 ) × 10 - 6 ( T / K - 303 ) ] cm 3 · mol - 1 for heavy water, with the numbers in parentheses expressing standard uncertainty. For heavy water, this work appears to be only the second gas phase measurement to date. For both ordinary and heavy water, this work agrees within $$0.15\ \%$$ 0.15 % with recent ab initio theoretical results for $$A_{\text {R}}$$ A R , but the comparison is affected by imperfect knowledge of dispersion. For ordinary water, the close agreement between the present work and theory suggests problems at the $$2\ \%$$ 2 % level in the low density limit of the reference formulation for refractivity.

Optical $$n(p,\ T_{90})$$ Measurement Suite 2: H$$_2$$O and D$$_2$$O

Egan,

Yang

2024

Optical n(p, T90) Measurement Suite 3: Results at $$\lambda = 1542\,\text{nm}$$

Egan,

Yang

2024

Single-isotherm n(p, T90) results are reported for the gases Ar, N2, H2O, and D2O at vacuum wavelength $$\lambda = 1542.383(1)$$ λ = 1542.383 ( 1 ) nm. The argon and nitrogen isotherms were measured near 303 K; the water isotherms were measured near 373 K. Combined with the two previous articles of this series, the present results beget several insights via dispersion analyses. The argon result is highly consistent with static measurement plus ab initio calculation of dispersion polarizability. The nitrogen result is nominally consistent with one recent experiment and the dipole oscillator strength distributions, but the present work offers a refined estimate of the molar refractivity at optical wavelengths. For ordinary and heavy water, the dispersion trend is nominally consistent with existing liquid measurements. However, water’s absorption features in the near-infrared preclude a reliable comparison of the present result with literature.

Expansivity of Fused Quartz Glass Measured Within $$6 \times 10^{-10}\,\text{K}^{-1}$$

Egan

2024

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 $$(\textrm{nm}{\cdot } \textrm{m}^{-1}){\cdot }\textrm{K}^{-1}$$ ( nm · m - 1 ) · K - 1 , 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 thin-film 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.