Observation of Magnetized Soliton Remnants in the Wake of Intense Laser Pulse Propagation through Plasmas

Slowly evolving, regularly spaced patterns have been observed in proton projection images of plasma channels drilled by intense ($\gtrsim {10}^{19}\mathrm{W}{\mathrm{cm}}^{-2}$) short ($\sim 1\mathrm{ps}$) laser pulses propagating in an ionized gas jet. The nature and geometry of the electromagnetic fields generating such patterns have been inferred by simulating the laser-plasma interaction and the following plasma evolution with a two-dimensional particle-in-cell code and the probe proton deflections by particle tracing. The analysis suggests the formation of rows of magnetized soliton remnants, with a quasistatic magnetic field associated with vortexlike electron currents resembling those of magnetic vortices.

Figure 1

Typical PPI data (acquired in a single laser shot). The probing times, relative to the arrival of the peak of the interaction pulse at $x=y=0$, are (a) $t=3.5\mathrm{ps}$, (b) $t=7\mathrm{ps}$, and (c) 17 ps [probe proton energies $\sim 12\mathrm{MeV}$ (a), $\sim 11\mathrm{MeV}$ (b) and $\sim 8\mathrm{MeV}$ (c)].

Figure 2

(a) Detail of PPI data showing bubble structures at late times ($t\sim 140\mathrm{ps}$, probe proton energy $\sim 8\mathrm{MeV}$). (b) Detail of a secondary filament exhibiting a multiple bubble pattern ($t\sim 37\mathrm{ps}$, probe proton energy $\sim 11\mathrm{MeV}$).

Figure 3

Details of the fields’ distribution in a single PS from PIC simulations. (a) Quasistatic electric field ($E_x$, $E_y$) at $t=875T_L$, (b) oscillating electric field $E_z$, (c) oscillating magnetic field ($B_x$, $B_y$), and (d) quasistatic magnetic field $B_z$ at $t=800T_L$.

Figure 4

Particle tracing simulations. (a) Simulated proton image and (b),(c) maps of the proton deflection $\delta \theta \sim \delta v_{py}/v_p$ arising from (b) the $\mathbf{E}$ field alone ($y$ scale enlarged for $x>-0.5\mathrm{mm}$ to highlight the $E_y$ focusing effect inside the channel) and from (c) the $\mathbf{B}$ field alone for the unmodulated channel. (d) Simulated proton image for the modulated channel.