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August 02, 2011

Cold electrons provide better nanoscale imaging

Effect of electron temperature on structural degradation.

By firing a series of laser beams into rubidium gas cooled to 70 millionths of a kelvin - close to absolute zero electrons are slowly released and allows them to control which part of the rubidium gas they target, producing specific shapes in the electron cloud that's released.

The work reported this week in the journal Nature Physics will eventually allow scientists to watch how proteins react to different chemicals or how microscopic cracks propagate in the turbine blades of jet engines.

Nature Physics - Arbitrarily shaped high-coherence electron bunches from cold atoms

Arbitrary electron density distribution bunches using spatially structured photoionization of a cold atom cloud.

Ultrafast electron diffractive imaging of nanoscale objects such as biological molecules and defects in solid-state devices provides crucial information on structure and dynamic processes: for example, determination of the form and function of membrane proteins, vital for many key goals in modern biological science, including rational drug design. High brightness and high coherence are required to achieve the necessary spatial and temporal resolution, but have been limited by the thermal nature of conventional electron sources and by divergence due to repulsive interactions between the electrons, known as the Coulomb explosion. It has been shown that, if the electrons are shaped into ellipsoidal bunches with uniform density, the Coulomb explosion can be reversed using conventional optics, to deliver the maximum possible brightness at the target. Here we demonstrate arbitrary and real-time control of the shape of cold electron bunches extracted from laser-cooled atoms. The ability to dynamically shape the electron source itself and to observe this shape in the propagated electron bunch provides a remarkable experimental demonstration of the intrinsically high spatial coherence of a cold-atom electron source, and the potential for alleviation of electron-source brightness limitations due to Coulomb explosion.

2 pages of supplemental information

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