Reflective Time-Resolved Wavefront-Images of Overcritical Ultra-Short-Pulse-Laser-Induced Plasma on Solid State Targets

When intense laser pulses hit solid surfaces, hot and dense plasmas are generated, which are a critical area of study with applications ranging from fusion to medical imaging. This paper presents an experimental technique for studying the early evolution of plasma using a Mach-Zehnder interferometer, which analyzes the phase distortions of a probe pulse reflected by the expanding plasma. The evaluation is not straightforward, but we show that by using specially designed ray tracing algorithms, we are able to calculate optical path differences of laser beams reflecting on plasma, providing us with insights into the plasma properties and development. First measurements are presented, displaying high spatial (∼ 10 µm), temporal (∼ 30 fs), and phase (∼ 0.1 rad) resolution, allowing quantitative data interpretation. In addition, we address key challenges for the correct alignment of this type of interferometer.