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Form and Wavefront Metrology

Working Group 4.21

Reference materials for Refractive Index 

Table of deliverable reference liquids

Medium Refractive index nD
n-Heptan 1.38777
Iso-Octan 1.39149
Tetrachlorethylen   1.50580

For the reference liquids, refractive index values and the associated temperature coefficient can be provided for the wavelengths 644 nm, 589 nm, 546 nm, 509 nm, 480 nm, 435 nm and 404 nm – with an uncertainty of approx. 1⋅10-5.
The temperature coefficient of the deliverable reference liquids amounts to approx. 0.5⋅10-3/K. The temperature coefficient is a very important part of the certified refractive index value and has to be taken into account in principle. If the user is not able to determine the absolute temperature in the refractometer under test with sufficiently small uncertainty, an increase in the uncertainty results.