Refractive index of shock-compressed liquid nitrogen up to 29 GPa

ABSTRACT

We report the equation of state and optical properties of shock-compressed liquid nitrogen (LN₂) by using a two-stage light-gas gun at pressure up to 29 GPa. Laser velocimetry measurements were used to investigate the transparency and refractive index of shocked LN₂ as a function of density. As the density increased with increasing pressure and temperature (13–25 GPa), the refractive index increased up to 27% of pre-shot index of LN₂. Evidently, such extreme conditions had no major influence on molecules, and no such dissociation was observed up to 25 GPa. The polarizability slightly decreased and thus supported the existence of intact diatomic molecular nitrogen. At 29 GPa, shocked LN₂ dissociated, showing that it probably changed to a highly reflecting fluid. Altogether, these experiments showed how the density affects the refractive index without any change in chemical bonding and allocates the condition at which the temperature-driven dissociation takes place.

KEYWORDS:

• Liquid nitrogen
• refractive index
• phase transition
• shock wave

Acknowledgements

The authors gratefully acknowledge our colleagues for the gas gun operations at Sichuan Provincial Key Laboratory of High Pressure Science and Technology, Southwest Jiaotong University, Chengdu. We would like to thank Mr. Ming-Jian Zhang for their help in setting up these experiments and Dr. Youjun Zhang for useful discussions.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

See the supplementary material for detailed information concerning the target design and apparatus.

Additional information

Funding

These experiments were supported by the School of Physical Science and Technology, Southwest Jiaotong University, Chengdu.