Photon emission by bremsstrahlung and nonlinear Compton scattering in the interaction of ultraintense laser and plasmas

By implementing the bremsstrahlung with Monte Carlo algorithm into the particle-in-cell code, the bremsstrahlung and nonlinear Compton scattering can be studied simultaneously in comparison way in the laser plasma interactions. The simulations are performed for the laser of different intensities interacting with either low-$Z$ or high-$Z$ target. The relative strength of the two photon emission from bremsstrahlung and nonlinear Compton scattering are compared. The result shows that when an ultrastrong intensity laser interacting with a thin and relative high $Z$ target the nonlinear Compton scattering is dominant, however, when the laser intensity $I < 10^{22} \mathrm{W/cm^2}$, the photon emission contributed by bremsstrahlung is comparable to that from nonlinear Compton scattering. In this case the usual ignorable of bremsstrahlung need to be reconsidered.