Concave pulse shaping of a circularly polarized laser pulse from non-uniform overdense plasmas

•Laser pulse shaping for a concave front by non-uniform overdense plasma was studied.•Particle-in-cell (PIC) simulations were used for the investigation.•A laser pulse can be shaped by a density-tapered overdense plasma.•The concave and sharp pulse front are useful in many laser–plasma applications.•They are important for ion acceleration, especially in the radiation pressure dominant regime.

Pulse shaping of circularly polarized laser pulses in nonuniform overdense plasmas are investigated numerically. Specifically we show by two-dimensional particle-in-cell simulations the generation of a concave pulse front of a circularly polarized, a few tens of petawatt laser pulse from a density-tapered, overdense plasma slab. The concept used for the transverse-directional shaping is the differential transmittance depending on the plasma density, and the laser intensity. For suitable selection of the slab parameters for the concave pulse shaping, we studied numerically the pulse transmittance, which can be used for further parameter design of the pulse shaping. The concavely shaped circularly polarized pulse is expected to add more freedom in controlling the ion-beam characteristics in the RPDA regime.