In this work we investigated the use of a plasma shutter in the form of a thin foil for laser-driven ion acceleration enhancement. It is shown with the help of 3D particle-in-cell simulations that the laser pulse intensity can be increased and its profile steepened after burning through the plasma shutter. The enhanced intensity profile has a positive effect on the subsequent ion acceleration from the main foil, significantly increasing the maximal ion energy. The pre-expansion of the plasma shutter caused by prepulses is investigated using 2D hydrodynamic simulations. A scheme using a double plasma shutter configuration (the first one filtering out the prepulses and the second one shaping the main pulse) is proposed.
An increasing intensity of the laser systems becomes available for experiments in the fields of particle acceleration, radiation sources and many other applications. The higher intensity of the laser irradiation is inherently accompanied by the growth of the amplified spontaneous emission (ASE) pedestal and other parasitic effects. Considering the forthcoming generation of multi-PW laser systems, the nanosecond and picosecond pedestals significantly exceed the respective plasma formation thresholds and may have detrimental effects on the laser--target interaction. One of the promising methods to mitigate these effects is the relativistic plasma shutter, where an ultra-thin foil is placed in front of the target. The initial interaction with the shutter increases the temporal contrast, where the pre-plasma is opaque for the pedestal, but relativistically transparent for the main pulse. Moreover, the created pre-plasma exhibits a focussing effect, increasing the effective intensity of the main pulse. Two-dimensional hydrodynamic simulations of the pedestal are performed, followed by PIC simulations of the main pulse. The parameters of the shutter, like density and thickness, are varied to optimize performance of the configuration.
The pre-plasma effects have been extensively studied experimentally and numerically and techniques for suppressing the pre-pulse are known widely. However, the increasing availability of the (multi-)PW-class laser systems enables to perform experiments with ultra-high laser intensities. The simulations of the pre-plasma formation and the effect on the main laser pulse must be reconsidered, since the systems are always limited in the contrast available and the created pre-plasma affects the interaction considerably. Our recent investigation of the topic revealed that the non-local transport of energy going beyond the paradigm of the diffusive approximation plays an important role in the process. An over-critical plateau is formed, where the main pulse is absorbed partially before reaching the solid target. Moreover, strong filamentation of the laser field occurs in the plasma. This effect is studied further by the means of the hydrodynamic simulations of the pre-plasma followed by the kinetic simulations of the interaction of the main pulse.