Femtosecond gas-phase mega-electron-volt ultrafast electron diffraction

X Shen; J P F Nunes; J Yang; R K Jobe; R K Li; Ming-Fu Lin; B Moore; M Niebuhr; S P Weathersby; T J A Wolf; C Yoneda; Markus Guehr; Martin Centurion; X J Wang

doi:10.1063/1.5120864

Femtosecond gas-phase mega-electron-volt ultrafast electron diffraction

Struct Dyn. 2019 Oct 15;6(5):054305. doi: 10.1063/1.5120864. eCollection 2019 Sep.

Authors

X Shen¹, J P F Nunes², J Yang, R K Jobe¹, R K Li¹, Ming-Fu Lin³, B Moore², M Niebuhr⁴, S P Weathersby¹, T J A Wolf⁵, C Yoneda¹, Markus Guehr⁴, Martin Centurion², X J Wang¹

Affiliations

¹ SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
² Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
³ Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
⁴ Institut für Physik und Astronomie, Universität Potsdam, 14476 Potsdam, Germany.
⁵ Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.

Abstract

The development of ultrafast gas electron diffraction with nonrelativistic electrons has enabled the determination of molecular structures with atomic spatial resolution. It has, however, been challenging to break the picosecond temporal resolution barrier and achieve the goal that has long been envisioned-making space- and-time resolved molecular movies of chemical reaction in the gas-phase. Recently, an ultrafast electron diffraction (UED) apparatus using mega-electron-volt (MeV) electrons was developed at the SLAC National Accelerator Laboratory for imaging ultrafast structural dynamics of molecules in the gas phase. The SLAC gas-phase MeV UED has achieved 65 fs root mean square temporal resolution, 0.63 Å spatial resolution, and 0.22 Å^-1 reciprocal-space resolution. Such high spatial-temporal resolution has enabled the capturing of real-time molecular movies of fundamental photochemical mechanisms, such as chemical bond breaking, ring opening, and a nuclear wave packet crossing a conical intersection. In this paper, the design that enables the high spatial-temporal resolution of the SLAC gas phase MeV UED is presented. The compact design of the differential pump section of the SLAC gas phase MeV UED realized five orders-of-magnitude vacuum isolation between the electron source and gas sample chamber. The spatial resolution, temporal resolution, and long-term stability of the apparatus are systematically characterized.