Theory and particle tracking simulations of a resonant radiofrequency deflection cavity in TM$_{110}$ mode for ultrafast electron microscopy

TL;DR

This paper develops a theoretical framework and simulations for RF deflecting cavities in TM$_{110}$ mode, enabling ultrafast electron microscopy with high temporal and spatial resolution by maintaining beam quality.

Contribution

It provides an analytic description of the cavity's optical transfer matrix and phase space propagation, demonstrating conditions to preserve beam quality for ultrafast imaging.

Findings

Analytic expressions for emittance and energy spread increase.

Beam focusing at cavity center preserves beam quality.

Simulations confirm high-resolution ultrafast microscopy feasibility.

Abstract

We present a theoretical description of resonant radiofrequency (RF) deflecting cavities in TM$_{110}$ mode as dynamic optical elements for ultrafast electron microscopy. We first derive the optical transfer matrix of an ideal pillbox cavity and use a Courant-Snyder formalism to calculate the 6D phase space propagation of a Gaussian electron distribution through the cavity. We derive closed, analytic expressions for the increase in transverse emittance and energy spread of the electron distribution. We demonstrate that for the special case of a beam focused in the center of the cavity, the low emittance and low energy spread of a high quality beam can be maintained, which allows high-repetition rate, ultrafast electron microscopy with 100 fs temporal resolution combined with the atomic resolution of a high-end TEM. This is confirmed by charged particle tracking simulations using a realistic cavity geometry, including fringe fields at the cavity entrance and exit apertures.