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 isstudied through analytic modeling and particle-in-cell simulations. The complex interplaybetween 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, wedevelop a fully relativistic model in 1-D treating both modes of ponderomotive light absorptionon equitable theoretical footing for the first time. Using this framework, analytic expressions forthe conversion efficiencies into hole punching ions and into hot electrons are derived. Solutionsfor the relativistically correct hole punching velocity and the hot electron Lorentz factor arealso calculated. Excellent agreement between analytic predictions and particle-in-cell simulationsis demonstrated, and astrophysical analogies are highlighted