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.
Highlights
The time-resolved investigation of ultrafast processes typically relies on pump-probe schemes with an adjustable delay between the pump pulse and the probe
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
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. We demonstrate both modes in start-to-end simulations of the UCLA Pegasus MeV microscope column
Summary
The time-resolved investigation of ultrafast processes typically relies on pump-probe schemes with an adjustable delay between the pump pulse and the probe. Time-resolved ultrafast electron diffraction (UED), in which the electron beam is streaked after it interacts with the diffraction sample, is an interesting possibility to resolve this, as it adds temporal information to a single shot image. A separation of the two pulses on the order of 10 ps thereby introduces a significant energy and chirp mismatch between the two beams This mismatch can be mitigated by using a linearizing RF cavity with higher frequency than the gun, which can flatten the output energy profile as a function of bunch arrival time. The paper is organized as follows: we describe the generation of electron beams with tunable delay in an RF gun and linearizer geometry We first apply this method to double-shot ultrafast electron diffraction (UED). We discuss detailed simulations of double-shot ultrafast electron microscopy (UEM) using two magnification stages composed by permanent magnet quadrupole based lenses
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