Order of magnitude increase in laser-target coupling at near-relativistic intensities using compound parabolic concentrators

TL;DR

This paper demonstrates that using compound parabolic concentrators on targets significantly enhances laser-target coupling efficiency and electron temperature at near-relativistic intensities, offering a practical solution for large-scale laser systems.

Contribution

The study introduces target-mounted compound parabolic concentrators that substantially improve laser energy coupling and electron heating in high-intensity laser interactions.

Findings

Nearly tenfold increase in conversion efficiency.

More than three times higher electron temperature.

Plasma confinement and turbulent laser fields are key mechanisms.

Abstract

Achieving a high conversion efficiency into relativistic electrons is central to short-pulse laser application and fundamentally relies on creating interaction regions with intensities ${\gg}10^{18}$~W/cm$^2$. Small focal length optics are typically employed to achieve this goal; however, this solution is impractical for large kJ-class systems that are constrained by facility geometry, debris concerns, and component costs. We fielded target-mounted compound parabolic concentrators to overcome these limitations and achieved nearly an order of magnitude increase to the conversion efficiency and more than tripled electron temperature compared to flat targets. Particle-in-cell simulations demonstrate that plasma confinement within the cone and formation of turbulent laser fields that develop from cone wall reflections are responsible for the improved laser-to-target coupling. {These passive target components can be used to improve the coupling efficiency for all high-intensity short-pulse laser applications, particularly at large facilities with long focal length optics.