Double-shot MeV electron diffraction and microscopy

Abstract

In this paper, we study by numerical simulations a time-resolved MeV electron scattering mode where two consecutive electron pulses are used to capture the evolution of a material sample on 10 ps time scales. The two electron pulses are generated by illuminating a photocathode in a radiofrequency photogun by two short laser pulses with adjustable delay. A streak camera/deflecting cavity is used after the sample to project the two electron bunches on two well separated regions of the detector screen. By using sufficiently short pulses, the 2D spatial information from each snapshot can be preserved. This “double-shot” technique enables the efficient capture of irreversible dynamics in both diffraction and imaging modes. In this work, we demonstrate both modes in start-to-end simulations of the UCLA Pegasus MeV microscope column.

Femtosecond phase-transition in hard x-ray excited bismuth

“…To date, however, to the best of our knowledge, neither experiments nor calculations have been able to describe the dynamics in a range above an absorbed dose of 1.2 eV/atom 13 , which is still well below a strong fast ionisation regime. In the interest of time-resolved studies, several experiments explored excitation regimes up to the regime of nonthermal melting in Bi 3,9,14 and in other materials with state-of-the-art techniques 15,16 . Up to now, structural studies at high temporal resolution (<100 fs) sensitive to the excitation of phonon modes in Bi have never been carried out neither in the non-thermal melting regime or above it.…”

Temporal magnification for streaked ultrafast electron diffraction and microscopy

“…An alternative approach, analogous to a streak camera, allows us to record the entire evolution of a single event by using a deflecting cavity to streak the temporal distribution of a beam along one of the transverse coordinates [9,10,11]. This typically requires the loss of one spatial dimension, and thus Email address: dcesar@ucla.edu (D. Cesar) the use of a slit to select a row from the diffraction pattern, however the loss of information can be avoided if the electron current profile is not continuous but made of discrete pulses which can be weakly separated by a fast deflector [12] or if compressed sensing techniques are used to reconstruct the voxels [13].…”