  From fusion dynamics in stars, to terrestrial lightning events, to new
prospects of energy production or novel light sources, hot dense plasmas are of
importance for an array of physical phenomena. Due to a plethora of
correlations in highly excited matter, direct probing of isolated dynamics
remains challenging. Here, the 32.8-nm emission of a high-harmonic seeded
laser-plasma amplifier (LPA), using eight-fold ionized Krypton as gain medium,
is ptychographically imaged in longitudinal direction in the extreme
ultraviolet (XUV). In excellent agreement with ab initio spatio-temporal
Maxwell-Bloch simulations, an overionization of krypton due to nonlinear
laser-plasma interactions is observed. This constitutes the first experimental
observation of the laser ion abundance reshaping a laser plasma amplifier. The
findings have direct implications for upscaling plasma-based XUV and X-ray
sources and allow modeling light-plasma interactions in extreme conditions,
similar to those of the early times of the universe, with direct experimental
verification.
