Relativistic Ultrafast Electron Microscopy: Single-Shot Diffraction Imaging with Femtosecond Electron Pulses

Jinfeng Yang,Yoichi Yoshida

doi:10.1155/2019/9739241

Abstract

We report on a single-shot diffraction imaging methodology using relativistic femtosecond electron pulses generated by a radio-frequency acceleration-based photoemission gun. The electron pulses exhibit excellent characteristics, including a root-mean-square (rms) illumination convergence of 31 ± 2 μrad, a spatial coherence length of 5.6 ± 0.4 nm, and a pulse duration of approximately 100 fs with (6.3 ± 0.6) × 106 electrons per pulse at 3.1 MeV energy. These pulses facilitate high-quality diffraction images of gold single crystals with a single shot. The rms spot width of the diffracted beams was obtained as 0.018 ± 0.001 Å−1, indicating excellent spatial resolution.

Highlights

Single-shot diffraction imaging with ultrashort Xray pulses generated from free-electron lasers has facilitated the study of structural dynamics of irreversible processes in material samples [2] and the acquisition of direct structural information in chemistry and biology before sample damage [3]
Ultrafast electron diffraction and microscopy (UED and UEM) with electron pulses are very promising techniques for the study of ultrafast structural dynamics in materials because electrons are complementary to X-rays in a number of ways [4]: (1) Electrons have a larger elastic scattering cross section and can be focused
In the demonstration for electron diffraction imaging, we used a single-crystalline gold film with a thickness of 10 nm, which was placed on a gold mesh

Summary

Introduction

Single-shot diffraction imaging with ultrashort Xray pulses generated from free-electron lasers has facilitated the study of structural dynamics of irreversible processes in material samples [2] and the acquisition of direct structural information in chemistry and biology before sample damage [3]. The most widely used UED [6,7,8] and UEM [9,10,11,12,13,14,15,16,17,18] instruments employ a static dc acceleration-based photoemission gun for generating short electron pulses with energies ≤ 200 keV. The space charge force of electrons in the nonrelativistic energy region broadens the pulse width and acts to increase energy spread and beam divergence This leads to a loss in spatial resolution [19]. To overcome the space charge problem, we have developed a prototype relativistic UEM with a radio-frequency (rf) acceleration-based photoemission electron gun [1]. The relativistic UEM using the rf gun Photocathode rf gun Condenser lenses

Objective lens

Experimental Results

Summary