Pulsed electron gun for electron diffraction at surfaces with femtosecond temporal resolution and high coherence length

2019 ◽  
Vol 90 (4) ◽  
pp. 045119 ◽  
Author(s):  
B. Hafke ◽  
T. Witte ◽  
C. Brand ◽  
Th. Duden ◽  
M. Horn-von Hoegen
Keyword(s):  
Electron Diffraction ◽  
Temporal Resolution ◽  
Coherence Length ◽  
Electron Gun ◽  
High Coherence

scholarly journals Femtosecond gas phase electron diffraction with MeV electrons

2016 ◽  
Vol 194 ◽  
pp. 563-581 ◽  
Author(s):  
Jie Yang ◽  
Markus Guehr ◽  
Theodore Vecchione ◽  
Matthew S. Robinson ◽  
Renkai Li ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Gas Phase ◽  
Spatial Resolution ◽  
Temporal Resolution ◽  
Timing Jitter ◽  
Electron Gun ◽  
Relativistic Electrons ◽  
New Device ◽  
Electron Pulses ◽  
Velocity Mismatch

We present results on ultrafast gas electron diffraction (UGED) experiments with femtosecond resolution using the MeV electron gun at SLAC National Accelerator Laboratory. UGED is a promising method to investigate molecular dynamics in the gas phase because electron pulses can probe the structure with a high spatial resolution. Until recently, however, it was not possible for UGED to reach the relevant timescale for the motion of the nuclei during a molecular reaction. Using MeV electron pulses has allowed us to overcome the main challenges in reaching femtosecond resolution, namely delivering short electron pulses on a gas target, overcoming the effect of velocity mismatch between pump laser pulses and the probe electron pulses, and maintaining a low timing jitter. At electron kinetic energies above 3 MeV, the velocity mismatch between laser and electron pulses becomes negligible. The relativistic electrons are also less susceptible to temporal broadening due to the Coulomb force. One of the challenges of diffraction with relativistic electrons is that the small de Broglie wavelength results in very small diffraction angles. In this paper we describe the new setup and its characterization, including capturing static diffraction patterns of molecules in the gas phase, finding time-zero with sub-picosecond accuracy and first time-resolved diffraction experiments. The new device can achieve a temporal resolution of 100 fs root-mean-square, and sub-angstrom spatial resolution. The collimation of the beam is sufficient to measure the diffraction pattern, and the transverse coherence is on the order of 2 nm. Currently, the temporal resolution is limited both by the pulse duration of the electron pulse on target and by the timing jitter, while the spatial resolution is limited by the average electron beam current and the signal-to-noise ratio of the detection system. We also discuss plans for improving both the temporal resolution and the spatial resolution.

Structure of Amorphous Films Using Direct Recording Electron Diffraction

1968 ◽  
Vol 26 ◽  
pp. 396-397 ◽  
Author(s):  
D. B. Dove
Keyword(s):  
Electron Diffraction ◽  
Diffraction Pattern ◽  
Electron Gun ◽  
Amorphous Films ◽  
Magnetic Lens ◽  
Small Aperture ◽  
Interatomic Distances ◽  
Electron Diffraction Technique ◽  
Direct Recording ◽  
Film Specimen

Vapor deposited layers of certain materials show a diffuse, amorphous diffraction pattern; carbon is an example. Such patterns may not be interpreted by identification of Bragg peaks, instead the intensity profile is measured with all possible precision and the data is then treated by computer, yielding what is, in effect, a spectrum of interatomic distances within the specimen.The direct recording electron diffraction technique is particularly suited to the measurement of diffuse patterns. The electron beam from a conventional electron gun and magnetic lens arrangement produces a transmission diffraction pattern of a thin film specimen. Coils beneath the specimen produce a magnetic field which deflects the diffraction pattern across a very small aperture.

scholarly journals A compact electron gun for time-resolved electron diffraction

2015 ◽  
Vol 86 (1) ◽  
pp. 013109 ◽  
Author(s):  
Matthew S. Robinson ◽  
Paul D. Lane ◽  
Derek A. Wann
Keyword(s):  
Electron Diffraction ◽  
Electron Gun ◽  
Time Resolved

A 150 kV High-Coherence Microscope

1974 ◽  
Vol 32 ◽  
pp. 412-413
Author(s):  
R. E. Worsham ◽  
W. W. Harris ◽  
J. E. Mann ◽  
E. G. Richardson ◽  
N. F. Ziegler
Keyword(s):  
Coherence Length ◽  
Spatial Information ◽  
Spherical Aberration ◽  
Wiener Filter ◽  
Energy Spread ◽  
Filter Function ◽  
Resolution Level ◽  
High Coherence ◽  
Illuminating Beam ◽  
Transmission Microscope

Welton has shown that if the illuminating beam in a conventional transmission microscope column has a transverse coherence length of 5°0 Å, or greater, and an energy spread ≤0.2 eV(rms), spatial information at the 0.5 Å resolution level would be attenuated by a factor of 2 and 1 Å information essentially unimpaired. The untreated micrographs, which would show a complex set of fringes with detail down to about 2.5 Å as set by spherical aberration, would require the application of a Wiener filter function to bring out the existing finer details. This microscope was designed to produce the high coherence required, to permit this method of correction for the spherical aberration, and to be limited in no other way in resolution down to <1Å.

scholarly journals Optical fiber-driven low-energy electron gun for time-resolved streak diffraction

2019 ◽  
Vol 205 ◽  
pp. 08016
Author(s):  
Chiwon Lee ◽  
H. Kassier Gunther ◽  
R. J. Dwayne Miller
Keyword(s):  
Electron Diffraction ◽  
Optical Fiber ◽  
Low Energy ◽  
Energy Electron ◽  
Electron Gun ◽  
Single Shot ◽  
Optical Fibres ◽  
Time Resolved ◽  
Low Energy Electron Diffraction ◽  
Low Energy Electron

The wave guiding feature of the optical fibre optical fibres is specifically exploited to construct a novel type of electron gun to realize single-shot low-energy electron diffraction experiments with the sub-picosecond resolution for studying irreversible samples.

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