Radially accelerating and autofocusing caustics in electron vortex beams

Abstract

Electron vortex beams (EVBs) carrying quantized orbital angular momentum significantly enhance the quantum state encoding and phase modulation capabilities of free electrons. However, conventional EVBs are constrained by linear propagation dynamics and coupling among different degrees of freedom, which limit their broader applicability. Here, we propose and experimentally demonstrate a radially accelerated autofocusing electron vortex beam (RAAF-EVB) that enables independent and precise control over key parameters, including a designed power-law radial acceleration trajectory, the initial ring radius, and the topological charge. Experimental results show that RAAF-EVBs maintain stable power-law caustic evolution across varying topological charges and superposition states, confirming robust decoupling among the designed trajectory, initial radius, and topological charge. The development of RAAF-EVBs provides a general framework for designing highly customizable structured electron beams, with promising applications in electron microscopy, quantum state manipulation, and particle physics.