Quantum electrodynamics (QED) effects in intense laser plasma interaction were investigated using Particle in Cell (PIC) simulations, specifically the generation of electron-positron pairs. Linearly polarized intense laser pulses were used to irradiate a thin foil (1 μm) with an intensity of 4×10 23 Wcm -2 . A scan of targets with varying Z (Al, Cu and Au) is investigated to determine the effect of target Z/density on electron-positron pair production. The total number of pairs created for Al and Cu targets is 10 14 and 10 13 respectively. In the case of Au, we did not observe any pair production to occur. We have also calculated the variation in electron energy in these targets. The results indicate that target Z plays a very important role with the laser interaction in the pair production process, which will be explained in this paper.

We study the photon emission by bremsstrahlung and nonlinear Compton scattering from interaction of ultraintense laser pulses with cone target and flat foil using particle-in-cell simulations. The simulations are performed for laser pulses interacting with Al and Au targets. The strength of the two mechanisms of photon emission from bremsstrahlung and nonlinear Compton scattering are compared. When an ultra-intense (I > 10 22 W/cm 2 ) laser interacts with a cone and a foil target, photon emission by bremsstrahlung is found to be comparable to that from nonlinear Compton scattering. The obtained electron energy as well as the energy and number of photons emitted were found to be higher in case of cone shaped target compared with that of a foil target. The enhanced photon emission from cone shaped target is attributed to the guiding or collimation of hot electrons towards the cone tip from the self-generated magnetic field and electrostatic field along the cone surface which pushes the hot electrons towards the tip.

We investigate the production of intense ү-rays following the interaction of ultraintense laser pulse with a hybrid combination of under-dense plasma associated with a thin foil of fully ionized Al or Cu or Au at the rear side. Relativistic electrons are accelerated following the interaction of high intensity laser pulses with an under-dense plasma. These electrons are then stopped by the thin foils attached to the rear side of the under-dense plasma. This results in the production of intense-ray bursts. So, the enhancement of photon generation is due to the under-dense plasma electrons interacting with different over-dense plasma. Using open-source PIC code EPOCH, we study the effect of different electron densities in the under-plasma on photon emission. Photon emission enhancement is observed by increasing the target Z in the hybrid structure. Hybrid structure can enhance photon emission; it can increase the photon energy and yield and improve photon beam divergence. Simulations were also performed to find the optimal under-dense plasma density for ү-ray production.

We report an experimental investigation on the proton acceleration from the interaction of intense
laser pulse of intensity about 10^20 Wcm−2 with a thin foil of Aluminum, Titanium and Gold of
thickness 2μm. Protons are accelerated via the TNSA mechanism from the rear surface of the target
and in addition, protons accelerated from the front surface were also detected on the Radio Chromic
films. Hollow proton rings could be seen on the radio chromic films corresponding to 1-3MeV protons.
The protons from the front surface are driven into the target and directed towards the rear side of
the target by the Kilotesla magnetic fields generated from the laser-plasma. The enhancement in
the proton number in the 1-3MeV range with a hollow beam profile in the experiments are in good
agreement with the observed strong magnetic field structures from the results of 2D Particle-In-Cell
simulations EPOCH and SMILEI.