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

We report the design and performance of a time-resolved electron diffraction apparatus capable of producing intense bunches with <200 fs rms duration, single digit micron probe sizes, and simultaneously long coherence length. 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 and perform proof-of-principle measurements of ultrafast heating in single crystal Au samples.