The coupling of laser energy to electrons is fundamental to almost all topics in intense laser-plasma interactions, including laser-driven particle and radiation generation, relativistic optics, inertial connement fusion and laboratory astrophysics. We report measurements of total energy absorption in foil targets ranging in thickness from 20 nm, for which the target remains opaque and surface interactions dominate, to 40 nm, for which expansion enables relativistic-induced transparency and volumetric interactions. We measure a total peak absorption of ~80% at an optimum thickness of ~380 nm. For thinner targets, for which some degree of transparency occurs, although the total absorption decreases, the number of energetic electrons escaping the target increases. 2D particle-in-cell simulations indicate that this results from direct laser acceleration of electrons as the intense laser pulse propagates within the target volume. The results point to a trade-off between total energy coupling to electrons and efficient acceleration to higher energies.
- laser energy
- energy absorption
Williamson, S. D. R., Gray, R. J., King, M., Wilson, R., Dance, R. J., Armstrong, C., ... McKenna, P. (2020). Energy absorption and coupling to electrons in the transition from surface- to volume-dominant intense laser-plasma interaction regimes. New Journal of Physics, . https://doi.org/10.1088/1367-2630/ab86df