Acceleration gradients in dielectric laser accelerators with triangular-shaped gratings

TL;DR

Dielectric laser accelerators (DLAs) are explored using triangular grating profiles to maximize on-chip accelerating gradients. The authors perform 3D PIC simulations in CST Studio Suite for 20 μm-long, 800 nm-period fused-silica structures driven by a plane wave of $E_0=1$ GV/m, comparing rectangular and triangular geometries, left- and right-handed orientations, and reflective gold coatings with a 10 MeV electron beam. The key results show that right-handed transparent DLAs with $\alpha=36^\circ$ reach $\Delta E \approx 4.1$ keV and $G \approx 205$ MeV/m, while reflective triangular DLAs (notably left-handed at $\alpha=20^\circ$) can reach $\Delta E \approx 3$ keV and $G \approx 150$ MeV/m; left-handed transparent profiles are comparatively inefficient, and rectangular references set baseline performance ($\Delta E \approx 1.1$ keV, $G \approx 55$–$65$ MeV/m). Field analysis reveals a dominant first spatial harmonic near $k \approx 1/\lambda_L \approx 1.25\,\mu\text{m}^{-1}$, indicating strong field localization and resonant interaction with relativistic beams. Overall, the work demonstrates that triangular DLAs—especially right-handed transparent and reflective left-handed configurations—can achieve high accelerating gradients, informing design strategies for compact on-chip accelerator modules.

Abstract

The study investigated transparent on-chip structures with a rectangular profile and triangular profiles with grating ridge base angles of $α= 36^\circ$, $30^\circ$, and $20^\circ$. Each triangular structure had both left- and right-handed profile orientations. For all variants, a modified version with a reflective gold coating was additionally considered. The maximum energy gains and accelerating gradients were determined and quantified for all structure classes: transparent and reflective (with both rectangular and triangular profiles).

Figures (9)

• Figure 1: Illustration of the particle acceleration principle in triangular on-chip structures: accelerating (a), neutral (b), and decelerating (c) field regions near the dielectric structure surface. Here, $E_0$ represents the maximum axial electric field value, therefore warm colors ($E/E_0 > 0$) correspond to the accelerating phase of the electric field acting on the electron, while cool colors ($E/E_0 < 0$) represent the decelerating phase. The accelerated electron is marked by a black circle.
• Figure 2: Scheme of the theoretical model for the numerical simulation of acceleration in a DLA with a triangular profile for transparent (a) dielectric and reflective (b) surfaces. This figure corresponds to the left-handed orientation of the triangular profile.
• Figure 3: Electron beam phase space "energy gain vs. longitudinal coordinate" in a DLA with a rectangular on-chip structure.
• Figure 4: Electron beam phase space "energy gain vs. longitudinal coordinate" in DLAs with a left-handed (a) and right-handed (b) transparent ridge orientations and a ridge base angle of $\alpha = 36^\circ$.
• Figure 5: Electron beam phase space "energy gain vs. longitudinal coordinate" in a DLA with a reflective rectangular on-chip structure.