Generating intense attosecond pulses and vectorizing polarization states from laser-plasma interactions

Abstract

Vector beams with spatially structured polarization and intertwined spin-orbital angular momentum (SAM-OAM) provide powerful degrees of freedom for tailoring light-matter interactions. While such structured beams are well established in the visible and infrared regimes, extending them to the extreme-ultraviolet (EUV) and soft X-ray (SXR) domains at relativistic intensities remains a major challenge. Here, we investigate the generation of higher-order harmonic vector beams driven by relativistic laser-plasma interactions. Combining theoretical analysis with three-dimensional particle-in-cell simulations, we elucidate the underlying physical mechanisms governing the transfer and conversion of polarization and orbital angular momentum during harmonic generation. We demonstrate that both the polarization topology and OAM of the emitted harmonics can be deterministically controlled by the topological charges of the driving field. Owing to the intrinsic properties of vector beams, either few-cycle driving pulses or vector polarization gating applied to multi-cycle pulses enable the production of intense isolated attosecond pulses featuring spiral wavefronts and spatially tailored polarization states. These results establish a pathway toward high-intensity structured light sources in the EUV and SXR regimes and open new opportunities for ultrafast and strong-field light-matter interaction studies with engineered angular momentum.

Figures (6)

• Figure 1: Schematic view: Generation of intense harmonic vector beams from laser-solid interactions. When an intense near-infrared vector pump beam (red) is normally incident on an overdense planar target, the resulting longitudinal ponderomotive force drives relativistic oscillations of electrons at the critical density surface. These oscillations reflect the incident light and emit high-order harmonic vector radiation (dark blue). The slices represent the intensity and polarization patterns of the incident and reflected harmonic vector beams in the transverse plane.
• Figure 2: (a) Spectra of reflected pulses for different vector pump beams. The magenta dashed line shows the spectral scaling law. (b) Spatiotemporal evolution of electron density at a fixed transverse position ($y=w_0, z=0$). (c)-(l) Transverse distribution of electron density at $x=12.76\mu$m for different moments, with (c)-(g) corresponding to ($l_L=3, l_R=-3$) and (h)-(l) corresponding to ($l_L=-1, l_R=2$).
• Figure 3: Characterization of harmonic vector beams extracted from 3D PIC simulations. The grayscale colormap shows the intensity distribution $I_V \propto E_{Vy}^2 + E_{Vz}^2$ of the vector beam in the transverse $(y,z)$ plane, while the red arrows represent the electric-field vectors. Blue solid lines mark radial lines of the polarization pattern. Different rows represent different types of the vector beam, corresponding to Tab. \ref{['tab1']}, while different columns are for different harmonic orders.
• Figure 4: Intensity and local electric field vectors of harmonic vector beams rotate with the longitudinal position. The parameter ($l_L = -1$, $l_R = 2$) is used. The grayscale colormap shows the intensity distribution, while the red arrows represent the electric-field vectors. Different rows are for different harmonic orders. For the $q$-th harmonic, intensity and local electric field vectors rotate with periods $\lambda_0/2q$ and $\lambda_0/q$, respectively.
• Figure 5: Generation of an isolated intense attosecond vector pulse driven by a near-single-cycle laser pulse with a FWHM duration of 2.40 fs. (a) Harmonic spectrum of the reflected light. The magenta dashed line indicates the spectral scaling law. (b) Intensity isosurface $(I_V/I_{V,max}=0.3)$ of the reflected vector beam filtered for the 5th-19th harmonics. (c) Lineout of the filtered field intensity at $y=-3.0 \mu$m and $z=2.16 \mu$m. (d-f) Transverse distributions at $x=9.0 \mu$m of the (d) $E_{Vy}$ and (e) $E_{Vz}$ electric-field components, and (f) the corresponding intensity $I_V \propto E_{Vy}^2 + E_{Vz}^2$, with in-plane electric-field vectors shown by red arrows.