Robust sub-50 fs cavity-laser phase stabilization for ultra-fast electron diffraction instruments

Martin Otto ,Laurent P René De Cotret,Bradley J Siwick,Mark J Stern

doi:10.1051/epjconf/201920508015

Abstract

A novel laser-RF cavity synchronization scheme was developed for ultrafast electron diffraction instruments. The approach directly generates a synchronized microwave tone by retrieving a phase-locked high-harmonic by photodetection. The radio-frequency cavity which performs electron pulse compression is detuning compensated using an active phase stabilization loop. Timing stability improved from 100 fs to 5 fs RMS and long-term time-zero stability improved to below our measurement resolution of 50 fs determined by pulse streaking.

Highlights

Unmodified by external fields, space-charge dynamics in ultrashort electron pulses result in a trade-off between pulse fluence and time resolution that is detrimental to ultrafast electron diffraction and imaging experiments
In this work we demonstrate a new approach [2] to laser-cavity synchronization and stabilization that provides electron pulse duration limited time-resolution over >10 hrs, effectively solving the jitter-problem in RF compressed UED experiments
We directly measure the change in the arrival time of the electron pulses with respect to a femtosecond optical pump pulse using an optically triggered 10 GHz streak camera similar to that presented in Ref. [3]

Summary

Introduction

Unmodified by external fields, space-charge dynamics in ultrashort electron pulses result in a trade-off between pulse fluence and time resolution that is detrimental to ultrafast electron diffraction and imaging experiments. A technique that compensates for space-charge driven pulse broadening, has been demonstrated to be very effective in the single shot limit yielding electron pulses below 100 fs at 100 keV [1]. The stability of the cavity-laser synchronization systems that have been employed to date are insufficient to provide pulse duration limited time-resolution in ultrafast electron diffraction instruments over the several hours required to acquired a full data-set.

Results

Conclusion