Role of plasma waves in rescattering processes in intense laser fields

TL;DR

The study analyzes how wakefield-generated plasma fields in a medium influence rescattering-based strong-field phenomena. By deriving a 1D hydrodynamic model and solving for the wakefield $E_s$ under different ionization scenarios, it identifies conditions where $E_s$ can compensate the electron's magnetic drift, potentially restoring plateau HHG and related NSDI/ATI processes. It also demonstrates, via TDSE, that the plasma field imprints satellites on XFID spectra—shifted by $\pm \omega_p$ or $\pm 2\omega_p$—which can reveal otherwise forbidden transition frequencies. These results open a pathway to both enhanced rescattering in plasmas and XFID spectroscopy that probes forbidden transitions.

Abstract

Rescattering of the photoelectron at its parent ion underlie a number of phenomena in intense laser field interaction with matter, such as high harmonic generation, attosecond pulse production, non-sequential double ionization, and others. These processes are unavoidably accompanied by the medium photoionization. The interaction of the laser pulse with the photoionization-induced plasma excites wakefield waves, which are self-consistently coupled plasma density and Langmuir waves. We study theoretically the effect of the electric field of the plasma wave on the rescattering processes. We show that this field can compensate for the magnetic drift of the rescattering electron, which otherwise dramatically suppresses the rescattering efficiency in intense low-frequency laser fields. Moreover, the presence of the plasma wave field leads to new lines in the spectrum emitted due to the XUV free-induction decay (XFID). Observation of these lines can allow, in particular, the detection of forbidden transition frequencies, thus providing new perspectives for XFID spectroscopy.

Figures (6)

• Figure 1: The normalized plasma field $E_s/A$ and the charge density $\rho/B$ for $n_i=const$ (panel a) and $n_i \ne const$ (panel b)) calculated for $D=4$ as functions of $\theta$. The normalized laser intensity (dashed black curve), the normalized plasma field (solid red and blue curves), the normalized charge density (dotted magenta curve), and the normalized plasma density (dash-dotted cyan curve).
• Figure 2: The normalized maximum plasma field achieved within the laser pulse (solid curves) and the amplitude of its oscillations after the pulse (dashed curves) as functions of $D$. Results for $n_i=const$ (red curves) and for $n_i \ne const$ (blue curves with circles). Note that the normalized amplitude of the charge density oscillations equals that of the plasma field oscillations.
• Figure 3: The normalized plasma field $E_s/A$ for $n_i=const$ (red curve) and $n_i \ne const$ (blue curve with circles) excited by two pulses with equal durations of $D=4$ and the delay between the pulses of $1.5 \times 2 \pi / \omega_{p}$.
• Figure 4: The fields of the the electromagnetic wave $\textbf{E}$ and $\textbf{H}$, its wave vector $\textbf{k}$, the electric field of the plasma wave $\textbf{E}_s$. The dotted curve shows the electron's trajectory before rescattering. The Lorentz force accelerates the electron in the pulse propagation direction and the electric field of the plasma wave accelerates it in the opposite one.
• Figure 5: The coefficient $g$ and the energy of the returning electron $\varepsilon$ as functions of $\varphi=\omega_0 \tau_{free}$, calculated for the quasi-classical electron's trajectory (note the logarithmic scale along the left vertical axis and the linear scale along the right one).