Diagnosing electron density profiles of laser-driven magnetized collisionless shocks with refractive imaging

Collisionless shocks are frequently observed in astrophysical plasmas and play a key role in energy dissipation and particle acceleration. However, the complexities of these shocks, especially at small scales, is challenging to understand through in situ observations alone. Laboratory settings can complement these observations by enabling diagnostic methods for high-resolution probing of plasma characteristics. In this work, we use refractive imaging diagnostics, specifically angular filter refractometry (AFR) and shadowgraphy, to measure electron density profiles across magnetized collisionless shocks. Shocks were created on the Omega EP laser facility by pushing a laser-driven piston plasma supersonically through a magnetized ambient plasma. AFR images are analyzed to determine extended density profiles from ambient plasma to the laser targets. In turn, shadowgraphy is used to isolate and diagnose localized profiles of strong density gradients. By combining these methods, we obtain both the general shape of the density profile, as well as details about the narrow shock features, including density compression at the shock front, shock width, and the gap between shock and piston plasma. This study highlights the capabilities of refractive imaging to quantitatively probe plasma densities and to validate models of collisionless shock formation and evolution.