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We use particle-in-cell (PIC) simulations and simple analytic models toinvestigate the laser-plasma interaction known as ponderomotive steepening.When normally incident laser light reflects at the critical surface of aplasma, the resulting standing electromagnetic wave modifies the electrondensity profile via the ponderomotive force, which creates peaks in theelectron density separated by approximately half of the laser wavelength. Whatis less well studied is how this charge imbalance accelerates ions towards theelectron density peaks, modifying the ion density profile of the plasma.Idealized PIC simulations with an extended underdense plasma shelf are used toisolate the dynamics of ion density peak growth for a 42 fs pulse from an 800nm laser with an intensity of 10$^{18}$ W cm$^{-2}$. These simulations exhibitsustained longitudinal electric fields of 200 GV m$^{-1}$, which producecounter-steaming populations of ions reaching a few keV in energy. We comparethese simulations to theoretical models, and we explore how ion energy dependson factors such as the plasma density and the laser wavelength, pulse duration,and intensity. We also provide relations for the strength of longitudinalelectric fields and an approximate timescale for the density peaks to develop.These conclusions may be useful investigating the phenomenon of ponderomotivesteepening as advances in laser technology allow shorter and more intensepulses to be produced at various wavelengths. We also discuss the parallelswith other work studying the interference from two counter-propagating laserpulses.

Particle-in-Cell Simulations of Density Peak Formation and Ion Acceleration from Short Pulse Laser-Driven Ponderomotive Steepening