Shock response of barium fluoride (BaF2) in planar impact experiments
Project conducted under Professor James Hawreliak; Institute for Shock Physics, Washington State University
In a 10-week internship taking place in Summer 2024, I conducted a project investigating the shock response of barium fluoride (BaF2) in high-pressure planar impact experiments. In the early 1970s, work conducted at WSU characterized the shock response of BaF2 at low pressures (P < 4GPa) [1]. Since it may be useful as an optical window in shock physics experiment (see caption describing experimental setup, bottom-right paragraph), there is an interest in its response to high-pressure impacts. This includes changes in its refractive index and whether or not it remains transparent.
My time in lab was spent preparing materials, conducting shock experiments, and analyzing wave profile data. The results of the first three experiments provided some crucial insights into its response to high-pressure shocking. Nevertheless, more work is required to characterize the material so it can be used as an optical window in future experiments.
[1] Dandekar, D. P., & Duvall, G. E. (1973). Characteristics of the shock induced transformation in BaF2. In Metallurgical Effects at High Strain Rates (pp. 185-200). Boston, MA: Springer US.
[2] Shapiro, M., Hunter, L., Hawreliak, J., & Jensen, B. Shock response of barium fluoride (BaF2) in planar impact experiments: optical properties under extreme compression [poster presentation]. Washington State University Summer 2024 Research Symposium, Pullman, WA, United States.
Above image shows target consisting of a barium fluoride single crystal bonded to a lithium fluoride (LiF) single crystal. The top surface has an aluminum vapor deposition. The entire piece is bonded to a target holder (aluminum ring with screw holes).
Left diagram shows side and back views of experimental setup [2]. Fiber optics send/receive pulses of light to determine the velocity of an interface/surface (in this case, the velocities of the BaF2 free surface and BaF2/LiF interface). This is achieved with Velocity Interferometry System for Any Reflector (VISAR). The data can then be used to calculate and infer the shock response of the BaF2 target.
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Note on optical windows: the optical window (LiF in this case) serves as a continuation of the material. It reduces the prominence of shock wave reflections once the shock wave reaches the back surface of the BaF2. Akin to the refraction of light as it passes from one medium to another, the more similar the materials are in shock impedance values, the less prominent the wave reflections.