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

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.

High-resolution movies of molecular rotational dynamics captured with ultrafast electron diffraction

“…We have also characterized the stability of the timing by measuring changes in the position of the alignment peaks over several hours. The measured timing drift over 4.5 h was 50 fs rms, which is comparable to state of the art facilities such as the MeV-UED setup at SLAC [36].…”

Laser-induced electron diffraction of the ultrafast umbrella motion in ammonia

“…The static geometric structure of molecules can be successfully determined through a variety of imaging and spectroscopic techniques 5 , such as conventional electron diffraction (CED) 6 , X-ray diffraction and crystallography 7 , optical and nuclear magnetic resonance (NMR) spectroscopies 8 , scanning tunneling microscopy (STM) 8 and atomic force microscopy (AFM) 8 . In particular, the timeresolved analogues of X-ray and electron diffraction, such as ultrafast X-ray diffraction (UXD) 9,10 and ultrafast electron diffraction (UED) [11][12][13][14][15][16][17][18] , have provided a wealth of dynamical information in molecules that contain atoms much heavier than hydrogen. As a result, their scattering signal in such molecules is very large and their respective dynamics occur on the hundreds-of-femtosecond timescale.…”

Molecular structure retrieval directly from laboratory-frame photoelectron spectra in laser-induced electron diffraction

“…Similar SD-based iterative algorithms have also been used in field-free UED and conventional electron diffraction to accurately extract bond lengths within a small forward scattering angle (i.e. <10°) 12 , 14 , 15 , 26 , 27 . The Fourier-transform LIED (FT-LIED) 14 , 21 , 23 method, also called fixed-angle broadband laser-driven electron scattering (FABLES) 8 , retrieves the DCS in the backward scattering direction (i.e.…”

“…< 10°). 12,14,15,26,27 The Fourier-transform LIED (FT-LIED) 14,21,23 method, also called fixed-angle broadband laser-driven electron scattering (FABLES) 8 , retrieves the DCS in the backward scattering direction (i.e. along the laser polarization frame, corresponding to 180°) at a range of scattering electron energies.…”