Topic/Type: 1.3 High intensity Laser Plasma Interaction, Poster

### Numerical investigation of ponderomotive force effect in an underdense plasma with a linear density profile

A. R. Niknam1, M. Hashemzadeh1, M. M. Montazeri2

1 Laser-Plasma Research Institute of Shahid Beheshti University, G. C., Evin, 1983963113, Tehran, Iran
2 Department of Physics, University of Qom, Qom, Iran

The ponderomotive force in interaction of ultrashort laser pulses with plasmas can cause various nonlinear phenomena [1-2]. This force is applied on electrons by the spatial variation of laser pulse intensity and it can change the plasma density profiles. The ponderomotive force which is applied on ions could be neglected because the ions are massive. In our previous works, by considering the ponderomotive force, we investigated the electric and magnetic field profiles of an intense laser pulse and the electron density variation in the plasma for different values of energy flux in nonrelativistic and weakly relativistic regimes [3-4]. In this work, we consider the nonlinear interaction between a high intense laser pulses and an underdense plasma with a linear density profile. This case models the interaction of a laser pulse with a solid target. We assume the laser energy flux $\small I=1\times10^{17}W/cm^2$, the electron temperature $\small T_e=10 keV$ and the incident laser wavelength $\small \lambda=0.8\mu m$. By using the momentum transfer and Maxwell?s equations and by considering the ponderomotive force and the linear density profile effects, we obtain the plasma dielectric permittivity and the nonlinear differential equation for the propagation of intense laser pulse in a cold underdense plasma. Therefore, for obtaining the electromagnetic fields in plasma, this intensely nonlinear differential equation must be solved by numerical procedures. We show that the profiles of the electric field and the magnetic field become nonsinusoidal. Also, the electron density distribution becomes highly peaked.

[1] W. L. Kruer, The physics of laser plasma interactions (Addison-Wesley Publishing Company) 1988.

[2] S. Eliezer, The interaction of high-power lasers with plasmas, (IOP Publishing Ltd) 2002.

[3] B. Shokri, and A. R. Niknam, Phys. Plasmas 13, 113110 (2006).

[4] A. R. Niknam, M. Hashemzadeh, and B. Shokri, Phys. Plasmas, 16, 033105 (2009).