Studying the Correction Factor of a Lithium Fluoride Crystal During its Shock Compression and Isoentropic Unloading

Abstract

Lithium fluoride (LiF) single crystals are widely used in experiments involving intense dynamic loading as a window for optical methods, such as VISAR or PDV. They are transparent and do not undergo phase transitions under shock compression up to ~200 GPa. To interpret experimental data obtained using such a window, it is necessary to introduce a correction coefficient. This coefficient links the apparent mass velocity obtained experimentally to the true mass velocity. While this coefficient is constant for stationary shock waves, it is affected by the spatial non-uniformity of the window's density for more complex flows. The study highlights the experimental investigations of shock-wave processes in lithium fluoride conducted under shock loading up to 90 GPa. Mathematical modeling of the experiments was also performed. For this purpose, the authors built a mathematical model of one-dimensional elastoplastic flows of the medium using the Prandtl–Reuss plasticity model, and constructed the equation of state for lithium fluoride. The correction coefficient was obtained in two ways: based on the dependence of the refractive index on density and the law of mass conservation on the shock wave, and based on the dependence of the optical path length of the laser beam on the density distribution in the material under study.