Description
High-power (>TW), short-pulse (<ps) laser systems are generating significant interest worldwide due to their numerous applications in science, technology, medicine and industry. Each of these applications relies upon the plasma that is initially produced by the laser's interaction with the target matter. These laser-plasmas range widely in spatial scales from microns to millimeters, and their dynamics can evolve on femtosecond to nanosecond timescales. Due to the sensitivity with which the plasma properties depend on the laser system, and the downstream effects of this initial plasma on the subsequent secondary sources and physics applications, diagnostics that capture a robust picture of their temporal and spatial evolution on a single shot must be developed for and demonstrated on high-power laser systems.
Studies of high-power-laser plasmas to-date have been limited by either temporal or spatial resolution or rely on scanning a variable, such as time or delay. Such measurements that use multiple laser shots to form a measurement cannot reliably distinguish between changes due to shot-to-shot variations and changes due to the variable being scanned. To address this problem, we present the development and demonstration of a diagnostic for the measurement of the spatial and temporal evolution of plasma density in a single shot [2]. Single-shot Advanced Plasma Probe HolographIc REconstruction (SAPPHIRE) uses a chirped probe pulse, a diffractive optical element, a self-referenced interferometer, and an interference bandpass filter to achieve high-fidelity electron density measurements suitable for underdense plasmas that exhibit cylindrical symmetry. It overcomes limitations in conventional diagnostics, such as reliance on shot-to-shot reproducibility, while capturing plasma dynamics on picosecond timescales with micron-level spatial resolution. The capabilities of SAPPHIRE are demonstrated through measurements of laser-driven plasma channels in gas jets, including the formation and expansion of plasma channels and the propagation of supersonic ionization fronts while revealing shot-to-shot variations in the plasma profiles. Experimental results are validated against theoretical models and scaling laws, underscoring the robustness and accuracy of this technique. By enabling ultrafast, high-resolution plasma diagnostics in a single exposure, SAPPHIRE represents a transformative advancement in plasma measurement technology.
[1] E Grace et al. Optica 12 1522 (2025).