A kiloelectron-volt ultrafast electron micro-diffraction apparatus using low emittance semiconductor photocathodes

Abstract

We report the design and performance of a time-resolved electron diffraction apparatus capable of producing intense bunches with simultaneously single digit micron probe size, long coherence length, and $200$ fs rms time resolution. We measure the 5d (peak) beam brightness at the sample location in micro-diffraction mode to be $7\times 10^{13}\mathrm{A}/{\text{m}}^2{\text{-rad}}^2$. To generate high brightness electron bunches, the system employs high efficiency, low emittance semiconductor photocathodes driven with a wavelength near the photoemission threshold at a repetition rate up to 250 kHz. We characterize spatial, temporal, and reciprocal space resolution of the apparatus. We perform proof-of-principle measurements of ultrafast heating in single crystal Au samples and compare experimental results with simulations that account for the effects of multiple-scattering.

13 pages, 10 figures, submitted to Structural Dynamics

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• Ultimate bunch length and emittance performance of an MeV ultrafast electron diffraction apparatus with a DC gun and a multi-cavity SRF linac
• Megahertz cycling of ultrafast structural dynamics enabled by nanosecond thermal dissipation
• Vector-based feedback of continuous wave radiofrequency compression cavity for ultrafast electron diffraction
• Ultrafast Electron Diffraction: Visualizing Dynamic States of Matter