Kinematic Constraints on Absorption of Ultraintense Laser Light

Abstract

We derive upper and lower bounds on the absorption of ultraintense laser light by solids as a function of fundamental laser and plasma parameters. These limits emerge naturally from constrained optimization techniques applied to a generalization of the laser-solid interaction as a strongly-driven, relativistic, two degree of freedom Maxwell-Vlasov system. We demonstrate that the extrema and the phase-space-averaged absorption must always increase with intensity, and increase most rapidly when $10^{18}<I_L{\lambda }_L^2<10^{20}$ W $\mu$m${}^2/$cm${}^2$. Our results indicate that the fundamental empirical trend towards increasing fractional absorption with irradiance therefore reflects the underlying phase space constraints.