Conservation laws and conversion efficiency in ultraintense laser-overdense plasma interactions
Particle coupling to the oscillatory and steady-state nonlinear force of an ultraintense laser is studied through analytic modeling and particle-in-cell simulations. The complex interplay between these absorption mechanisms—corresponding, respectively, to “hot” electrons and “hole punching” ions—is central to the viability of many ultraintense laser applications. Yet, analytic work to date has focused only on limiting cases of this key problem. In this paper, we develop a fully relativistic model in 1-D treating both modes of ponderomotive light absorption on equitable theoretical footing for the first time. Using this framework, analytic expressions for the conversion efficiencies into hole punching ions and into hot electrons are derived. Solutions for the relativistically correct hole punching velocity and the hot electron Lorentz factor are also calculated. Excellent agreement between analytic predictions and particle-in-cell simulations is demonstrated, and astrophysical analogies are highlighted.