Optically modulated free-electron computational ghost imaging for long-working-distance surface characterization

Scanning electron microscopy faces a fundamental resolution-aberration trade-off, which is exacerbated in scanning ultrafast electron microscopy by the long working distances required for pump-probe integration and low electron flux. We report an optically modulated free-electron computational ghost imaging framework to overcome these constraints. By employing laser-induced ponderomotive modulation to generate structured electron illumination, we record the total secondary-electron yield via a bucket detector. Critically, spherical aberration is integrated into the forward model for wavefront engineering, rendering the system intrinsically aberration-resilient. Image reconstruction is performed using a modified stochastic gradient descent algorithm. Numerical simulations demonstrate high-fidelity surface characterization under long-working-distance and low-flux conditions, where conventional SEM performance degrades. This paradigm provides a robust pathway for high-resolution imaging in aberration-dominated and signal-starved electron microscopy platforms.