# Solving the Jitter Problem in Microwave Compressed Ultrafast Electron Diffraction Instruments: Robust Sub-50 fs Cavity-Laser Phase Stabilization

## TL;DR

This paper presents a method to compress electron pulses in ultrafast electron diffraction using phase-locked microwave signals and a stabilization system, achieving sub-50 fs timing stability and overcoming previous synchronization limitations.

## Contribution

The authors introduce a robust phase stabilization system for microwave cavity-laser synchronization, enabling sub-50 fs electron pulse timing stability in UED instruments.

## Key findings

- Microwave timing stability improved from 100 fs to 5 fs RMS.
- Long-term electron pulse stability exceeds 50 fs over 10 hours.
- Achieved sub-50 fs electron pulses in UED without laser-microwave synchronization limits.

## Abstract

We demonstrate the compression of electron pulses in a high-brightness ultrafast electron diffraction (UED) instrument using phase-locked microwave signals directly generated from a mode-locked femtosecond oscillator. Additionally, a continuous-wave phase stabilization system that accurately corrects for phase fluctuations arising in the compression cavity from both power amplification and thermal drift induced detuning was designed and implemented. An improvement in the microwave timing stability from 100 fs to 5 fs RMS is measured electronically and the long-term arrival time stability ($>$10 hours) of the electron pulses improves to below our measurement resolution of 50 fs. These results demonstrate sub-relativistic ultrafast electron diffraction with compressed pulses that is no longer limited by laser-microwave synchronization.