Refractive Index of Helium to 100 GPa

The optical properties of helium are of great interest to high energy density science as helium is a major constituent of gas giants and white dwarfs [1-2]. We statically precompressed helium at room temperature to an initial density of ~0.4 g/cm³ (P~1 GPa) and used high power lasers to reverberation compress the sample to a peak pressure of ~100 GPa on a near-isentropic pathway. Velocity interferometry measurements revealed the refractive index of helium versus density. The experiments used a newly developed pitted diamond-anvil cell [3], which can sustain a higher static pressure for a given pusher thickness compared to prior designs. These data complement prior work on shock-compressed helium and the new target design opens up new opportunities for controlling the dynamic compression pathways in fluid samples.



[1] L. Stixrude, R. Jeanloz, Proc. Natl. Acad. Sci. 105, 11071-11075 (2008).

[2] M. Preising, R. Redmer, Contrib. Plasma Phys. 61, e202100105 (2021).

[3] PALM Scientific, 2538 Braddock Dr., Naperville, IL 60565.