Investigation of the Raman backward radiation evolutions leading to chaos in the interaction of intense laser pulses with Helium atoms

This paper investigates the stochastic heating of electrons caused by Raman backscatter radiations during the interaction of a laser pulse with helium atoms by means of a parallel particle-in-cell (PIC) code. At different propagation times, the self-consistent laser pulse changes are investigated via the space-time Fourier transform of the transverse vector potential. It is demonstrated that, since ionization has a striking influence on the emission of Raman backscattered radiation, it also plays an important role in the threshold of electron stochastic heating. As demonstrated by the experiments, the Raman backscattered radiations are initiated by a strong initial noise when a laser pulse has a long rise time, 100 fs. Hence, the fundamental condition for the chaos threshold is satisfied sooner by examining ionization effects. In this manner, stochastic heating of the electrons is initiated more rapidly than if the laser pulse were emitted in the preplasma. Accordingly, in concurrence with the idea of chaos, the electrons acquire more energy via the stochastic mechanism in the field-ionized plasma.