Lawrence Livermore National Laboratory's National Ignition Facility (NIF) is the hottest place on Earth for the briefest of moments during an experiment. Now, it can be one of the brightest places thanks to the Advanced Radiographic Capability (ARC), NIF's laser-within-a-laser. How this is possible and how it's measured is detailed in a paper in Physics of Plasmas titled "Development and scaling of MeV X-ray radiography at NIF-ARC."
