Fig. 1. Schematic of LWFA setup driven by 1 PW laser based on (top) an MPP and (bottom) an ordinary OAP. The combination of an MPP and a short-focal-length OAP is able to compress the focusing system to less than 1 m. The stimulated wakefield is shown by the electron density (gray) and the acceleration field E_z (red and blue). The transverse profiles at the entrance and the wakefield structures are compared in the plots below the schematic.

Fig. 2. (a) and (b) Variation of on-axis accelerating field E_z in the simulation window (red and blue) and the on-axis electron density (yellow) for (a) the reflected pulse and (b) the injected pulse. (c) and (d) Corresponding evolution of the electron energy spectrum (gray) and the final spectrum (blue).

Fig. 3. Scaling laws of electron energy gain (black) and the reduction ratio of the MPP geometry. The electron energy gain depends on both the laser power and the plasma density.

Fig. 4. Geometry of the simulation of reflection by an MPP, where f is the focal length of the MPP and z₀ the distance between the focus of the OAP and the MPP.

Fig. 5. (a)–(c) Electric fields (red and blue) and electron density (black) in the x–y plane at ct = 60, 100, and 500 μm. (d) Spectrum of generated harmonics for the CP incident pulse (black solid), reflected (red dashed), reflected without preplasma (gray dotted), and LP reflected (blue dot-dashed). All spectra are normalized to the laser base frequency.

Fig. 6. (a) Reflected pulse at ct = 500 μm in x–y plane for f = 675 μm without preplasma. (b) E_y field in y–z plane sliced at the black dashed line in (a). (c) Profile of E_y at the red/blue dashed lines in (b) (red/blue solid) and corresponding phases relative to the pulse center (red/blue dashed). The gray dashed line is the expected E_y profile. (d)–(f) Results for f = 675 μm with preplasma. (g)–(i) Results for f = 750 μm with preplasma.