A compact femtosecond electron diffractometer with pump-probe and streak camera modes

Ultrafast electron diffraction with ultrabright photoemission guns is proven to be a powerful technique to probe transient laser-induced fundamental molecular phenomena and photo-triggered chemical reactions in the fs-ps time scales whereby leading to production of so-called molecular movies in an attempt to relate structure and dynamics [1]. A number of factors restrict achieving higher temporal and spatial resolutions, including electron pulse stretching due to Coulomb repulsion. Our compact 100 keV electron gun chamber design prevents significant pulse broadening and spatial divergence to occur prior to the scattering of electrons at the sample plane. An external electromagnetic lens is conveniently used to produce the diffraction pattern on the image plane. Using a range of home-built noncollinear optical parametric amplifiers, solid crystalline samples can be excited within a range of UV-Vis wavelengths. Furthermore, the chamber is equipped with a radiofrequency cavity for a single-shot mode of operation as an electron streak camera [2]. This leads to a time resolution of 30 fs, and an anticipated spatial resolution of <0.01A to resolve atomic motions which is desired to investigate a host of reaction modes of interest.

[1] R. J. Dwayne Miller, “Femtosecond crystallography with ultrabright electrons and X-rays: Capturing chemistry in action”, Science 343 (2014).

[2] D. S. Badali, and R. J. Dwayne Miller, “Robust reconstruction of time-resolved diffraction from ultrafast streak cameras”, Struct. Dyn. 4 (2017).