Optics and Photonics Society of Iran

 High harmonics can be generated thanks to the interaction high power femtosecond laser and plasmas. In this research, by particle in cell (PIC) simulation of the plasma density, the variation in the generated harmonics is investigated and as a result the optimum spectrum of the harmonics is achieved. The lower atomic number can be produced the higher harmonics. Based on the primary explanation of the high harmonic generations known as Doppler shift effect in reflection of the electromagnetic wave from the surface of the plasma oscillation, the amplitude of the plasma surface is theoretically derived, and it is shown that the amplitude is maximum for lower nuclei number of atoms. Finally the PIC simulation is applied for the different atomic number of the nuclei and it shown that the surface amplitude oscillation is in good agreement with the simulations.