Programmable shaping of electron beams

A new technique that combines electron microscopy and laser technology enables programmable, arbitrary shaping of electron beams. It can potentially be used for optimising electron optics and for adaptive electron microscopy, maximising sensitivity while minimising beam-induced damage. The technology has been demonstrated by Austrian and German researchers, with their results published in the journal Physical Review X.

When light passes through turbulent or dense material, eg, the Earth’s atmosphere or a millimetre-thick tissue, standard imaging technologies experience significant limitations in the imaging quality. Scientists therefore place deformable mirrors in the optical path of the telescope or microscope, which cancel out the undesired effects. This so-called adaptive optics has led to many breakthroughs in astronomy and deep-tissue imaging.

However, this level of control has not yet been achieved in electron optics even though many applications in materials science and structural biology demand it. In electron optics, scientists use beams of electrons instead of light to image structures with atomic resolution. Usually, static electromagnetic fields are used to steer and focus the electron beams.

Researchers from the University of Vienna and the University of Siegen have now shown that it is possible to deflect electron beams almost arbitrarily using high-intensity, shaped light fields, which repel electrons. Kapitza and Dirac first predicted this effect in 1933, and the first experimental demonstrations became possible with the advent of high-intensity pulsed lasers.

The Vienna-based experiment makes use of our ability to shape light. A laser pulse is shaped by a spatial light modulator and interacts with a counter-propagating, synchronised pulsed electron beam in a modified scanning electron microscope. This enables imprinting on demand transverse phase shifts to the electron wave, enabling unprecedented control over electron beams.

The potential of this innovative technology is demonstrated by creating convex and concave electron lenses and by generating complex electron intensity distributions. As pointed out by lead author Marius Constantin Chirita Mihaila, from the University of Vienna, “We are writing with the laser beam in the transverse phase of the electron wave. Our experiments pave the way for wavefront shaping in pulsed electron microscopes with thousands of programmable pixels. In the future, parts of your electron microscope may be made from light.”

In contrast to other competing electron-shaping technologies, the scheme is programmable, and avoids losses, inelastic scattering and instabilities due to the degradation of material diffraction elements. Thomas Juffmann, head of the group at the University of Vienna, added, “Our shaping technique enables aberration correction and adaptive imaging in pulsed electron microscopes. It can be used to adjust your microscope to the specimens you study to maximise sensitivity.”

Image caption: Recent experiments at the University of Vienna show that light (red) can be used to arbitrarily shape electron beams (yellow), opening new possibilities in electron microscopy and metrology. Image ©stefaneder.at, University of Vienna

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