Kinetic approach to THz radiation generation at femtosecond laser pulse ponderomotive effect on plasma in magnetic field

For a semibounded plasma in a constant magnetic field and interacting with short laser pulse, a kinetic equation is derived, which makes it possible to describe the low-frequency movements of electrons. In the linear approximation in laser radiation intensity the solution of kinetic equation is obtained taking into account mirror reflection of electrons by the plasma surface. Using this solution, we derived low-frequency currents generated by low-frequency field and ponderomotive force that changes during the pulse affect. Under the assumption that characteristic spatial scales of changes in the low-frequency field and ponderomotive force exceed the Larmor radius of electrons, we studied low-frequency currents near the plasma surface. If the electron cyclotron frequency exceeds the inverse pulse duration, then low-frequency currents differ from their values in a homogeneous plasma only at a distance from the surface not exceeding several Larmor radii. Taking this fact into account, a solution to the equation for low-frequency field in the plasma was obtained. The terahertz (THz) magnetic field generated by nonlinear currents is found. It is shown that the maximum value of the generated field is attained at cyclotron frequency comparable with the product of the plasma frequency square and laser pulse duration.

Figure 1

Dependence of the function $G_{xx}(\xi ,\lambda )$ on $\xi$ for several values of $\lambda =0.1,0.6,0.9$.

Figure 2

Dependence of the function $G_{yx}(\xi ,\lambda )$ on $\xi$ for several values of $\lambda =0.1,0.6,0.9$.

Figure 3

Dependence of the function $G_{yy}(\xi ,\lambda )$ on $\xi$ for several values of $\lambda =0.1,0.3,0.6,0.9$. The right scale refers to the curve with $\lambda =0.1$, the left scale refers to the rest curves.

Figure 4

Dependence of the value $B_z(0,t)/B_m\left({\mathrm{\Omega }}_{★}\right)$ on the dimensionless time $t/t_p$ for different values of the ratio $\mathrm{\Omega }/{\mathrm{\Omega }}_{★}=0.1,0.3,1.0$.