Measurement of refractive index and equation of state in dense He, H2, H2O, Ne under high pressure in a diamond-anvil cell

TL;DR

This study accurately measures the refractive index of dense hydrogen, helium, water, and neon under high pressure using interferometry, revealing electronic changes and enabling precise phase transition and equation of state analysis.

Contribution

It introduces a high-precision interferometric method to measure refractive index and volume of transparent media under high pressure, providing new insights into electronic changes and phase transitions.

Findings

Refractive index measurements up to 35 GPa for H, He, H2O, Ne.

Observation of significant electronic changes with pressure.

Ability to determine the equation of state with ~1% accuracy.

Abstract

We present an accurate determination of the refractive index of hydrogen, helium, H2O and neon up to 35 GPa at ambient temperature. The experimental method is based on the combination of two interferometric signals of the Fabry-Perot cavity containing the sample in the diamond anvil cell. The data are put in perspective through the variation of the molecular polarisability with density. Significant electronic changes are observed. Interesting possibilities of the method are also illustrated: the high precision to finely probe phase transition; the simultaneous measurement of the volume to obtain the equation of state of transparent media with around 1 % accuracy.