Abstract
We describe the spatial coherence properties of a cold atom electron source in the framework of a quasihomogeneous wavefield. The model is used as the basis for direct measurements of the transverse spatial coherence length of electron bunches extracted from a cold atom electron source. The coherence length is determined from the measured visibility of a propagated electron distribution with a sinusoidal profile of variable spatial frequency. The electron distribution was controlled via the intensity profile of an atomic excitation laser beam patterned with a spatial light modulator. We measure a lower limit to the coherence length at the source of lc = 7.8 ± 0.9 nm.
Highlights
Electron probes are an important tool for nanometre scale investigations, for example the determination of membrane protein structures [1]
The spatial distribution of the electron pulse was observed on a phosphor screen attached to a micro channel plate (MCP) charge amplifier
Temperatures as low as T < 10 ± 5 K have been measured for a cold atom electron source (CAES) [13] indicating a characteristic coherence length of lc > 10 ± 3 nm
Summary
Electron probes are an important tool for nanometre scale investigations, for example the determination of membrane protein structures [1]. Improvements in electron sources have enabled increased spatial and temporal resolution beyond optical alternatives [2]. Ultrafast electron diffraction (UED) is an emerging technique for obtaining atomic-level structural dynamics at sub-picosecond timescales, such as atomic motion and phase transitions [3,4,5]. Ultrafast diffraction has the potential to capture images before sample damage occurs, essential to imaging biological specimens with sub-nanometre resolution [6, 7]. Conventional photoemission sources use high energy laser pulses to generate hot electrons at high current. Sub-100 fs 0.25 pC electron bunches have been extracted from a photoemission source, enabling demonstration of single-shot diffraction from a crystalline gold foil [10]
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