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

TL;DR

This paper presents a novel ultrafast electron micro-diffraction setup using low emittance semiconductor photocathodes, achieving high brightness, micron probe size, and 200 fs time resolution for studying ultrafast phenomena.

Contribution

The work introduces a high-brightness, time-resolved electron diffraction apparatus with a novel photocathode design and detailed characterization, enabling advanced ultrafast material studies.

Findings

Achieved 200 fs temporal resolution and micron-scale spatial resolution.

Demonstrated ultrafast heating measurements in gold crystals.

Measured high beam brightness of 7×10^{13} A/m^2-rad^2 at the sample.

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.